The inventions, researches and writings of Nikola Tesla
by Thomas Commerford Martin · English · Gutenberg #39272 · 1,011,911 chars · public domain (US)
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Title: The inventions, researches and writings of Nikola Tesla
Author: Thomas Commerford Martin
Release date: March 26, 2012 [eBook #39272]
Language: English
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*** START OF THE PROJECT GUTENBERG EBOOK THE INVENTIONS, RESEARCHES AND WRITINGS OF NIKOLA TESLA ***
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THE INVENTIONS
RESEARCHES AND WRITINGS
OF
NIKOLA TESLA
TO HIS COUNTRYMEN
IN EASTERN EUROPE THIS RECORD OF
THE WORK ALREADY ACCOMPLISHED BY
NIKOLA TESLA
IS RESPECTFULLY DEDICATED
[Illustration: Nikola Tesla]
THE INVENTIONS
RESEARCHES AND WRITINGS
OF
NIKOLA TESLA
WITH SPECIAL REFERENCE TO HIS WORK IN POLYPHASE
CURRENTS AND HIGH POTENTIAL LIGHTING
BY
THOMAS COMMERFORD MARTIN
Editor THE ELECTRICAL ENGINEER; Past-President American Institute
Electrical Engineers
1894
THE ELECTRICAL ENGINEER
NEW YORK
D. VAN NOSTRAND COMPANY,
NEW YORK.
Entered according to Act of Congress in the year 1893 by
T. C. MARTIN
in the office of the Librarian of Congress at Washington
Press of McIlroy & Emmet, 36 Cortlandt St., N. Y.
PREFACE.
The electrical problems of the present day lie largely in the economical
transmission of power and in the radical improvement of the means and
methods of illumination. To many workers and thinkers in the domain of
electrical invention, the apparatus and devices that are familiar,
appear cumbrous and wasteful, and subject to severe limitations. They
believe that the principles of current generation must be changed, the
area of current supply be enlarged, and the appliances used by the
consumer be at once cheapened and simplified. The brilliant successes of
the past justify them in every expectancy of still more generous
fruition.
The present volume is a simple record of the pioneer work done in such
departments up to date, by Mr. Nikola Tesla, in whom the world has
already recognized one of the foremost of modern electrical
investigators and inventors. No attempt whatever has been made here to
emphasize the importance of his researches and discoveries. Great ideas
and real inventions win their own way, determining their own place by
intrinsic merit. But with the conviction that Mr. Tesla is blazing a
path that electrical development must follow for many years to come, the
compiler has endeavored to bring together all that bears the impress of
Mr. Tesla's genius, and is worthy of preservation. Aside from its value
as showing the scope of his inventions, this volume may be of service as
indicating the range of his thought. There is intellectual profit in
studying the push and play of a vigorous and original mind.
Although the lively interest of the public in Mr. Tesla's work is
perhaps of recent growth, this volume covers the results of full ten
years. It includes his lectures, miscellaneous articles and
discussions, and makes note of all his inventions thus far known,
particularly those bearing on polyphase motors and the effects obtained
with currents of high potential and high frequency. It will be seen that
Mr. Tesla has ever pressed forward, barely pausing for an instant to
work out in detail the utilizations that have at once been obvious to
him of the new principles he has elucidated. Wherever possible his own
language has been employed.
It may be added that this volume is issued with Mr. Tesla's sanction and
approval, and that permission has been obtained for the re-publication
in it of such papers as have been read before various technical
societies of this country and Europe. Mr. Tesla has kindly favored the
author by looking over the proof sheets of the sections embodying his
latest researches. The work has also enjoyed the careful revision of the
author's friend and editorial associate, Mr. Joseph Wetzler, through
whose hands all the proofs have passed.
DECEMBER, 1893.
T. C. M.
CONTENTS.
PART I.
POLYPHASE CURRENTS.
CHAPTER I.
BIOGRAPHICAL AND INTRODUCTORY. 3
CHAPTER II.
A NEW SYSTEM OF ALTERNATING CURRENT MOTORS AND TRANSFORMERS. 7
CHAPTER III.
THE TESLA ROTATING MAGNETIC FIELD.--MOTORS WITH CLOSED
CONDUCTORS.--SYNCHRONIZING MOTORS.--ROTATING FIELD TRANSFORMERS. 9
CHAPTER IV.
MODIFICATIONS AND EXPANSIONS OF THE TESLA POLYPHASE SYSTEMS. 26
CHAPTER V.
UTILIZING FAMILIAR TYPES OF GENERATORS OF THE CONTINUOUS CURRENT
TYPE. 31
CHAPTER VI.
METHOD OF OBTAINING DESIRED SPEED OF MOTOR OR GENERATOR. 36
CHAPTER VII.
REGULATOR FOR ROTARY CURRENT MOTORS. 45
CHAPTER VIII.
SINGLE CIRCUIT, SELF-STARTING SYNCHRONIZING MOTORS. 50
CHAPTER IX.
CHANGE FROM DOUBLE CURRENT TO SINGLE CURRENT MOTORS. 56
CHAPTER X.
MOTOR WITH "CURRENT LAG" ARTIFICIALLY SECURED. 58
CHAPTER XI.
ANOTHER METHOD OF TRANSFORMATION FROM A TORQUE TO A SYNCHRONIZING
MOTOR. 62
CHAPTER XII.
"MAGNETIC LAG" MOTOR. 67
CHAPTER XIII.
METHOD OF OBTAINING DIFFERENCE OF PHASE BY MAGNETIC SHIELDING. 71
CHAPTER XIV.
TYPE OF TESLA SINGLE-PHASE MOTOR. 76
CHAPTER XV.
MOTORS WITH CIRCUITS OF DIFFERENT RESISTANCE. 79
CHAPTER XVI.
MOTOR WITH EQUAL MAGNETIC ENERGIES IN FIELD AND ARMATURE. 81
CHAPTER XVII.
MOTORS WITH COINCIDING MAXIMA OF MAGNETIC EFFECT IN ARMATURE AND
FIELD. 83
CHAPTER XVIII.
MOTOR BASED ON THE DIFFERENCE OF PHASE IN THE MAGNETIZATION OF
THE INNER AND OUTER PARTS OF AN IRON CORE. 88
CHAPTER XIX.
ANOTHER TYPE OF TESLA INDUCTION MOTOR. 92
CHAPTER XX.
COMBINATIONS OF SYNCHRONIZING MOTOR AND TORQUE MOTOR. 95
CHAPTER XXI.
MOTOR WITH A CONDENSER IN THE ARMATURE CIRCUIT. 101
CHAPTER XXII.
MOTOR WITH CONDENSER IN ONE OF THE FIELD CIRCUITS. 106
CHAPTER XXIII.
TESLA POLYPHASE TRANSFORMER. 109
CHAPTER XXIV.
A CONSTANT CURRENT TRANSFORMER WITH MAGNETIC SHIELD BETWEEN
COILS OF PRIMARY AND SECONDARY. 113
PART II.
THE TESLA EFFECTS WITH HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS.
CHAPTER XXV.
INTRODUCTORY.--THE SCOPE OF THE TESLA LECTURES. 119
CHAPTER XXVI.
THE NEW YORK LECTURE. EXPERIMENTS WITH ALTERNATE CURRENTS OF VERY
HIGH FREQUENCY, AND THEIR APPLICATION TO METHODS OF ARTIFICIAL
ILLUMINATION, MAY 20, 1891. 145
CHAPTER XXVII.
THE LONDON LECTURE. EXPERIMENTS WITH ALTERNATE CURRENTS OF HIGH
POTENTIAL AND HIGH FREQUENCY, FEBRUARY 3, 1892. 198
CHAPTER XXVIII.
THE PHILADELPHIA AND ST. LOUIS LECTURE. ON LIGHT AND OTHER HIGH
FREQUENCY PHENOMENA, FEBRUARY AND MARCH, 1893. 294
CHAPTER XXIX.
TESLA ALTERNATING CURRENT GENERATORS FOR HIGH FREQUENCY. 374
CHAPTER XXX.
ALTERNATE CURRENT ELECTROSTATIC INDUCTION APPARATUS. 392
CHAPTER XXXI.
"MASSAGE" WITH CURRENTS OF HIGH FREQUENCY. 394
CHAPTER XXXII.
ELECTRIC DISCHARGE IN VACUUM TUBES. 396
PART III.
MISCELLANEOUS INVENTIONS AND WRITINGS.
CHAPTER XXXIII.
METHOD OF OBTAINING DIRECT FROM ALTERNATING CURRENTS. 409
CHAPTER XXXIV.
CONDENSERS WITH PLATES IN OIL. 418
CHAPTER XXXV.
ELECTROLYTIC REGISTERING METER. 420
CHAPTER XXXVI.
THERMO-MAGNETIC MOTORS AND PYRO-MAGNETIC GENERATORS. 424
CHAPTER XXXVII.
ANTI-SPARKING DYNAMO BRUSH AND COMMUTATOR. 432
CHAPTER XXXVIII.
AUXILIARY BRUSH REGULATION OF DIRECT CURRENT DYNAMOS. 438
CHAPTER XXXIX.
IMPROVEMENT IN DYNAMO AND MOTOR CONSTRUCTION. 448
CHAPTER XL.
TESLA DIRECT CURRENT ARC LIGHTING SYSTEM. 451
CHAPTER XLI.
IMPROVEMENT IN UNIPOLAR GENERATORS. 465
PART IV.
APPENDIX: EARLY PHASE MOTORS AND THE TESLA OSCILLATORS.
CHAPTER XLII.
MR. TESLA'S PERSONAL EXHIBIT AT THE WORLD'S FAIR. 477
CHAPTER XLIII.
THE TESLA MECHANICAL AND ELECTRICAL OSCILLATORS. 486
PART I.
POLYPHASE CURRENTS.
CHAPTER I.
BIOGRAPHICAL AND INTRODUCTORY.
As an introduction to the record contained in this volume of Mr. Tesla's
investigations and discoveries, a few words of a biographical nature
will, it is deemed, not be out of place, nor other than welcome.
Nikola Tesla was born in 1857 at Smiljan, Lika, a borderland region of
Austro-Hungary, of the Serbian race, which has maintained against Turkey
and all comers so unceasing a struggle for freedom. His family is an old
and representative one among these Switzers of Eastern Europe, and his
father was an eloquent clergyman in the Greek Church. An uncle is to-day
Metropolitan in Bosnia. His mother was a woman of inherited ingenuity,
and delighted not only in skilful work of the ordinary household
character, but in the construction of such mechanical appliances as
looms and churns and other machinery required in a rural community.
Nikola was educated at Gospich in the public school for four years, and
then spent three years in the Real Schule. He was then sent to Carstatt,
Croatia, where he continued his studies for three years in the Higher
Real Schule. There for the first time he saw a steam locomotive. He
graduated in 1873, and, surviving an attack of cholera, devoted himself
to experimentation, especially in electricity and magnetism. His father
would have had him maintain the family tradition by entering the Church,
but native genius was too strong, and he was allowed to enter the
Polytechnic School at Gratz, to finish his studies, and with the object
of becoming a professor of mathematics and physics. One of the machines
there experimented with was a Gramme dynamo, used as a motor. Despite
his instructor's perfect demonstration of the fact that it was
impossible to operate a dynamo without commutator or brushes, Mr. Tesla
could not be convinced that such accessories were necessary or
desirable. He had already seen with quick intuition that a way could be
found to dispense with them; and from that time he may be said to have
begun work on the ideas that fructified ultimately in his rotating field
motors.
In the second year of his Gratz course, Mr. Tesla gave up the notion of
becoming a teacher, and took up the engineering curriculum. His studies
ended, he returned home in time to see his father die, and then went to
Prague and Buda-Pesth to study languages, with the object of qualifying
himself broadly for the practice of the engineering profession. For a
short time he served as an assistant in the Government Telegraph
Engineering Department, and then became associated with M. Puskas, a
personal and family friend, and other exploiters of the telephone in
Hungary. He made a number of telephonic inventions, but found his
opportunities of benefiting by them limited in various ways. To gain a
wider field of action, he pushed on to Paris and there secured
employment as an electrical engineer with one of the large companies in
the new industry of electric lighting.
It was during this period, and as early as 1882, that he began serious
and continued efforts to embody the rotating field principle in
operative apparatus. He was enthusiastic about it; believed it to mark a
new departure in the electrical arts, and could think of nothing else.
In fact, but for the solicitations of a few friends in commercial
circles who urged him to form a company to exploit the invention, Mr.
Tesla, then a youth of little worldly experience, would have sought an
immediate opportunity to publish his ideas, believing them to be worthy
of note as a novel and radical advance in electrical theory as well as
destined to have a profound influence on all dynamo electric machinery.
At last he determined that it would be best to try his fortunes in
America. In France he had met many Americans, and in contact with them
learned the desirability of turning every new idea in electricity to
practical use. He learned also of the ready encouragement given in the
United States to any inventor who could attain some new and valuable
result. The resolution was formed with characteristic quickness, and
abandoning all his prospects in Europe, he at once set his face
westward.
Arrived in the United States, Mr. Tesla took off his coat the day he
arrived, in the Edison Works. That place had been a goal of his
ambition, and one can readily imagine the benefit and stimulus derived
from association with Mr. Edison, for whom Mr. Tesla has always had the
strongest admiration. It was impossible, however, that, with his own
ideas to carry out, and his own inventions to develop, Mr. Tesla could
long remain in even the most delightful employ; and, his work now
attracting attention, he left the Edison ranks to join a company
intended to make and sell an arc lighting system based on some of his
inventions in that branch of the art. With unceasing diligence he
brought the system to perfection, and saw it placed on the market. But
the thing which most occupied his time and thoughts, however, all
through this period, was his old discovery of the rotating field
principle for alternating current work, and the application of it in
motors that have now become known the world over.
Strong as his convictions on the subject then were, it is a fact that
he stood very much alone, for the alternating current had no well
recognized place. Few electrical engineers had ever used it, and the
majority were entirely unfamiliar with its value, or even its essential
features. Even Mr. Tesla himself did not, until after protracted effort
and experimentation, learn how to construct alternating current
apparatus of fair efficiency. But that he had accomplished his purpose
was shown by the tests of Prof. Anthony, made in the of winter 1887-8,
when Tesla motors in the hands of that distinguished expert gave an
efficiency equal to that of direct current motors. Nothing now stood in
the way of the commercial development and introduction of such motors,
except that they had to be constructed with a view to operating on the
circuits then existing, which in this country were all of high
frequency.
The first full publication of his work in this direction--outside his
patents--was a paper read before the American Institute of Electrical
Engineers in New York, in May, 1888 (read at the suggestion of Prof.
Anthony and the present writer), when he exhibited motors that had been
in operation long previous, and with which his belief that brushes and
commutators could be dispensed with, was triumphantly proved to be
correct. The section of this volume devoted to Mr. Tesla's inventions in
the utilization of polyphase currents will show how thoroughly from the
outset he had mastered the fundamental idea and applied it in the
greatest variety of ways.
Having noted for years the many advantages obtainable with alternating
currents, Mr. Tesla was naturally led on to experiment with them at
higher potentials and higher frequencies than were common or approved
of. Ever pressing forward to determine in even the slightest degree the
outlines of the unknown, he was rewarded very quickly in this field
with results of the most surprising nature. A slight acquaintance with
some of these experiments led the compiler of this volume to urge Mr.
Tesla to repeat them before the American Institute of Electrical
Engineers. This was done in May, 1891, in a lecture that marked, beyond
question, a distinct departure in electrical theory and practice, and
all the results of which have not yet made themselves fully apparent.
The New York lecture, and its successors, two in number, are also
included in this volume, with a few supplementary notes.
Mr. Tesla's work ranges far beyond the vast departments of polyphase
currents and high potential lighting. The "Miscellaneous" section of
this volume includes a great many other inventions in arc lighting,
transformers, pyro-magnetic generators, thermo-magnetic motors,
third-brush regulation, improvements in dynamos, new forms of
incandescent lamps, electrical meters, condensers, unipolar dynamos, the
conversion of alternating into direct currents, etc. It is needless to
say that at this moment Mr. Tesla is engaged on a number of interesting
ideas and inventions, to be made public in due course. The present
volume deals simply with his work accomplished to date.
CHAPTER II.
A NEW SYSTEM OF ALTERNATING CURRENT MOTORS AND TRANSFORMERS.
The present section of this volume deals with polyphase currents, and
the inventions by Mr. Tesla, made known thus far, in which he has
embodied one feature or another of the broad principle of rotating field
poles or _resultant attraction_ exerted on the armature. It is needless
to remind electricians of the great interest aroused by the first
enunciation of the rotating field principle, or to dwell upon the
importance of the advance from a single alternating current, to methods
and apparatus which deal with more than one. Simply prefacing the
consideration here attempted of the subject, with the remark that in
nowise is the object of this volume of a polemic or controversial
nature, it may be pointed out that Mr. Tesla's work has not at all been
fully understood or realized up to date. To many readers, it is
believed, the analysis of what he has done in this department will be a
revelation, while it will at the same time illustrate the beautiful
flexibility and range of the principles involved. It will be seen that,
as just suggested, Mr. Tesla did not stop short at a mere rotating
field, but dealt broadly with the shifting of the resultant attraction
of the magnets. It will be seen that he went on to evolve the
"multiphase" system with many ramifications and turns; that he showed
the broad idea of motors employing currents of differing phase in the
armature with direct currents in the field; that he first described and
worked out the idea of an armature with a body of iron and coils closed
upon themselves; that he worked out both synchronizing and torque
motors; that he explained and illustrated how machines of ordinary
construction might be adapted to his system; that he employed condensers
in field and armature circuits, and went to the bottom of the
fundamental principles, testing, approving or rejecting, it would
appear, every detail that inventive ingenuity could hit upon.
Now that opinion is turning so emphatically in favor of lower
frequencies, it deserves special note that Mr. Tesla early recognized
the importance of the low frequency feature in motor work. In fact his
first motors exhibited publicly--and which, as Prof. Anthony showed in
his tests in the winter of 1887-8, were the equal of direct current
motors in efficiency, output and starting torque--were of the low
frequency type. The necessity arising, however, to utilize these motors
in connection with the existing high frequency circuits, our survey
reveals in an interesting manner Mr. Tesla's fertility of resource in
this direction. But that, after exhausting all the possibilities of this
field, Mr. Tesla returns to low frequencies, and insists on the
superiority of his polyphase system in alternating current distribution,
need not at all surprise us, in view of the strength of his convictions,
so often expressed, on this subject. This is, indeed, significant, and
may be regarded as indicative of the probable development next to be
witnessed.
Incidental reference has been made to the efficiency of rotating field
motors, a matter of much importance, though it is not the intention to
dwell upon it here. Prof. Anthony in his remarks before the American
Institute of Electrical Engineers, in May, 1888, on the two small Tesla
motors then shown, which he had tested, stated that one gave an
efficiency of about 50 per cent. and the other a little over sixty per
cent. In 1889, some tests were reported from Pittsburgh, made by Mr.
Tesla and Mr. Albert Schmid, on motors up to 10 H. P. and weighing about
850 pounds. These machines showed an efficiency of nearly 90 per cent.
With some larger motors it was then found practicable to obtain an
efficiency, with the three wire system, up to as high as 94 and 95 per
cent. These interesting figures, which, of course, might be supplemented
by others more elaborate and of later date, are cited to show that the
efficiency of the system has not had to wait until the present late day
for any demonstration of its commercial usefulness. An invention is none
the less beautiful because it may lack utility, but it must be a
pleasure to any inventor to know that the ideas he is advancing are
fraught with substantial benefits to the public.
CHAPTER III.
THE TESLA ROTATING MAGNETIC FIELD.--MOTORS WITH CLOSED
CONDUCTORS.--SYNCHRONIZING MOTORS.--ROTATING FIELD TRANSFORMERS.
The best description that can be given of what he attempted, and
succeeded in doing, with the rotating magnetic field, is to be found in
Mr. Tesla's brief paper explanatory of his rotary current, polyphase
system, read before the American Institute of Electrical Engineers, in
New York, in May, 1888, under the title "A New System of Alternate
Current Motors and Transformers." As a matter of fact, which a perusal
of the paper will establish, Mr. Tesla made no attempt in that paper to
describe all his work. It dealt in reality with the few topics
enumerated in the caption of this chapter. Mr. Tesla's reticence was no
doubt due largely to the fact that his action was governed by the wishes
of others with whom he was associated, but it may be worth mention that
the compiler of this volume--who had seen the motors running, and who
was then chairman of the Institute Committee on Papers and Meetings--had
great difficulty in inducing Mr. Tesla to give the Institute any paper
at all. Mr. Tesla was overworked and ill, and manifested the greatest
reluctance to an exhibition of his motors, but his objections were at
last overcome. The paper was written the night previous to the meeting,
in pencil, very hastily, and under the pressure just mentioned.
In this paper casual reference was made to two special forms of motors
not within the group to be considered. These two forms were: 1. A motor
with one of its circuits in series with a transformer, and the other in
the secondary of the transformer. 2. A motor having its armature circuit
connected to the generator, and the field coils closed upon themselves.
The paper in its essence is as follows, dealing with a few leading
features of the Tesla system, namely, the rotating magnetic field,
motors with closed conductors, synchronizing motors, and rotating field
transformers:--
The subject which I now have the pleasure of bringing to your notice is
a novel system of electric distribution and transmission of power by
means of alternate currents, affording peculiar advantages, particularly
in the way of motors, which I am confident will at once establish the
superior adaptability of these currents to the transmission of power and
will show that many results heretofore unattainable can be reached by
their use; results which are very much desired in the practical
operation of such systems, and which cannot be accomplished by means of
continuous currents.
Before going into a detailed description of this system, I think it
necessary to make a few remarks with reference to certain conditions
existing in continuous current generators and motors, which, although
generally known, are frequently disregarded.
In our dynamo machines, it is well known, we generate alternate currents
which we direct by means of a commutator, a complicated device and, it
may be justly said, the source of most of the troubles experienced in
the operation of the machines. Now, the currents so directed cannot be
utilized in the motor, but they must--again by means of a similar
unreliable device--be reconverted into their original state of alternate
currents. The function of the commutator is entirely external, and in no
way does it affect the internal working of the machines. In reality,
therefore, all machines are alternate current machines, the currents
appearing as continuous only in the external circuit during their
transit from generator to motor. In view simply of this fact, alternate
currents would commend themselves as a more direct application of
electrical energy, and the employment of continuous currents would only
be justified if we had dynamos which would primarily generate, and
motors which would be directly actuated by, such currents.
But the operation of the commutator on a motor is twofold; first, it
reverses the currents through the motor, and secondly, it effects
automatically, a progressive shifting of the poles of one of its
magnetic constituents. Assuming, therefore, that both of the useless
operations in the systems, that is to say, the directing of the
alternate currents on the generator and reversing the direct currents on
the motor, be eliminated, it would still be necessary, in order to cause
a rotation of the motor, to produce a progressive shifting of the poles
of one of its elements, and the question presented itself--How to
perform this operation by the direct action of alternate currents? I
will now proceed to show how this result was accomplished.
[Illustration: FIG. 1.]
[Illustration: FIG. 1a.]
[Illustration: FIG. 2.]
[Illustration: FIG. 2a.]
In the first experiment a drum-armature was provided with two coils at
right angles to each other, and the ends of these coils were connected
to two pairs of insulated contact-rings as usual. A ring was then made
of thin insulated plates of sheet-iron and wound with four coils, each
two opposite coils being connected together so as to produce free poles
on diametrically opposite sides of the ring. The remaining free ends of
the coils were then connected to the contact-rings of the generator
armature so as to form two independent circuits, as indicated in Fig. 9.
It may now be seen what results were secured in this combination, and
with this view I would refer to the diagrams, Figs. 1 to 8_a_. The field
of the generator being independently excited, the rotation of the
armature sets up currents in the coils C C_{1}, varying in strength and
direction in the well-known manner. In the position shown in Fig. 1, the
current in coil C is nil, while coil C_{1} is traversed by its maximum
current, and the connections may be such that the ring is magnetized by
the coils c_{1} c_{1}, as indicated by the letters N S in Fig. 1_a_,
the magnetizing effect of the coils c c being nil, since these coils
are included in the circuit of coil C.
[Illustration: FIG. 3.]
[Illustration: FIG. 3a.]
In Fig. 2, the armature coils are shown in a more advanced position,
one-eighth of one revolution being completed. Fig. 2_a_ illustrates the
corresponding magnetic condition of the ring. At this moment the coil
C_{1} generates a current of the same direction as previously, but
weaker, producing the poles n_{1} s_{1} upon the ring; the coil C also
generates a current of the same direction, and the connections may be
such that the coils c c produce the poles n s, as shown in Fig. 2_a_.
The resulting polarity is indicated by the letters N S, and it will be
observed that the poles of the ring have been shifted one-eighth of the
periphery of the same.
[Illustration: FIG. 4.]
[Illustration: FIG. 4a.]
In Fig. 3 the armature has completed one quarter of one revolution. In
this phase the current in coil C is a maximum, and of such direction as
to produce the poles N S in Fig. 3_a_, whereas the current in coil C_{1}
is nil, this coil being at its neutral position. The poles N S in Fig.
3_a_ are thus shifted one quarter of the circumference of the ring.
Fig. 4 shows the coils C C in a still more advanced position, the
armature having completed three-eighths of one revolution. At that
moment the coil C still generates a current of the same direction as
before, but of less strength, producing the comparatively weaker poles
n s in Fig. 4_a_. The current in the coil C_{1} is of the same strength,
but opposite direction. Its effect is, therefore, to produce upon the
ring the poles n_{1} s_{1}, as indicated, and a polarity, N S, results,
the poles now being shifted three-eighths of the periphery of the ring.
[Illustration: FIG. 5.]
[Illustration: FIG. 5a.]
In Fig. 5 one half of one revolution of the armature is completed, and
the resulting magnetic condition of the ring is indicated in Fig. 5_a_.
Now the current in coil C is nil, while the coil C_{1} yields its
maximum current, which is of the same direction as previously; the
magnetizing effect is, therefore, due to the coils, c_{1} c_{1} alone,
and, referring to Fig. 5_a_, it will be observed that the poles N S are
shifted one half of the circumference of the ring. During the next half
revolution the operations are repeated, as represented in the Figs. 6 to
8_a_.
[Illustration: FIG. 6.]
[Illustration: FIG. 6a.]
A reference to the diagrams will make it clear that during one
revolution of the armature the poles of the ring are shifted once around
its periphery, and, each revolution producing like effects, a rapid
whirling of the poles in harmony with the rotation of the armature is
the result. If the connections of either one of the circuits in the ring
are reversed, the shifting of the poles is made to progress in the
opposite direction, but the operation is identically the same. Instead
of using four wires, with like result, three wires may be used, one
forming a common return for both circuits.
[Illustration: FIG. 7.]
[Illustration: FIG. 7_a_.]
This rotation or whirling of the poles manifests itself in a series of
curious phenomena. If a delicately pivoted disc of steel or other
magnetic metal is approached to the ring it is set in rapid rotation,
the direction of rotation varying with the position of the disc. For
instance, noting the direction outside of the ring it will be found that
inside the ring it turns in an opposite direction, while it is
unaffected if placed in a position symmetrical to the ring. This is
easily explained. Each time that a pole approaches, it induces an
opposite pole in the nearest point on the disc, and an attraction is
produced upon that point; owing to this, as the pole is shifted further
away from the disc a tangential pull is exerted upon the same, and the
action being constantly repeated, a more or less rapid rotation of the
disc is the result. As the pull is exerted mainly upon that part which
is nearest to the ring, the rotation outside and inside, or right and
left, respectively, is in opposite directions, Fig. 9. When placed
symmetrically to the ring, the pull on the opposite sides of the disc
being equal, no rotation results. The action is based on the magnetic
inertia of iron; for this reason a disc of hard steel is much more
affected than a disc of soft iron, the latter being capable of very
rapid variations of magnetism. Such a disc has proved to be a very
useful instrument in all these investigations, as it has enabled me to
detect any irregularity in the action. A curious effect is also produced
upon iron filings. By placing some upon a paper and holding them
externally quite close to the ring, they are set in a vibrating motion,
remaining in the same place, although the paper may be moved back and
forth; but in lifting the paper to a certain height which seems to be
dependent on the intensity of the poles and the speed of rotation, they
are thrown away in a direction always opposite to the supposed movement
of the poles. If a paper with filings is put flat upon the ring and the
current turned on suddenly, the existence of a magnetic whirl may easily
be observed.
To demonstrate the complete analogy between the ring and a revolving
magnet, a strongly energized electro-magnet was rotated by mechanical
power, and phenomena identical in every particular to those mentioned
above were observed.
Obviously, the rotation of the poles produces corresponding inductive
effects and may be utilized to generate currents in a closed conductor
placed within the influence of the poles. For this purpose it is
convenient to wind a ring with two sets of superimposed coils forming
respectively the primary and secondary circuits, as shown in Fig. 10. In
order to secure the most economical results the magnetic circuit should
be completely closed, and with this object in view the construction may
be modified at will.
[Illustration: FIG. 8.]
[Illustration: FIG. 8_a_.]
The inductive effect exerted upon the secondary coils will be mainly due
to the shifting or movement of the magnetic action; but there may also
be currents set up in the circuits in consequence of the variations in
the intensity of the poles. However, by properly designing the generator
and determining the magnetizing effect of the primary coils, the latter
element may be made to disappear. The intensity of the poles being
maintained constant, the action of the apparatus will be perfect, and
the same result will be secured as though the shifting were effected by
means of a commutator with an infinite number of bars. In such case the
theoretical relation between the energizing effect of each set of
primary coils and their resultant magnetizing effect may be expressed by
the equation of a circle having its centre coinciding with that of an
orthogonal system of axes, and in which the radius represents the
resultant and the co-ordinates both of its components. These are then
respectively the sine and cosine of the angle _a_ between the radius and
one of the axes (_OX_). Referring to Fig. 11, we have r^2 = x^2 + y^2;
where x = r cos _a_, and y = r sin _a_.
Assuming the magnetizing effect of each set of coils in the transformer
to be proportional to the current--which may be admitted for weak
degrees of magnetization--then x = Kc and y = Kc^1, where K is a
constant and c and c^1 the current in both sets of coils respectively.
Supposing, further, the field of the generator to be uniform, we have
for constant speed
c^1 = K^1 sin _a_ and
c = K^1 sin (90 deg. + _a_) = K^1 cos _a_,
where K^1 is a constant. See Fig. 12.
Therefore,
x = Kc = K K^1 cos _a_;
y = Kc^1 = K K^1 sin _a_; and
K K^1 = r.
[Illustration: FIG. 9.]
That is, for a uniform field the disposition of the two coils at right
angles will secure the theoretical result, and the intensity of the
shifting poles will be constant. But from r^2 = x^2 + y^2 it follows
that for y = 0, r = x; it follows that the joint magnetizing effect
of both sets of coils should be equal to the effect of one set when at
its maximum action. In transformers and in a certain class of motors the
fluctuation of the poles is not of great importance, but in another
class of these motors it is desirable to obtain the theoretical result.
In applying this principle to the construction of motors, two typical
forms of motor have been developed. First, a form having a comparatively
small rotary effort at the start but maintaining a perfectly uniform
speed at all loads, which motor has been termed synchronous. Second, a
form possessing a great rotary effort at the start, the speed being
dependent on the load.
These motors may be operated in three different ways: 1. By the
alternate currents of the source only. 2. By a combined action of these
and of induced currents. 3. By the joint action of alternate and
continuous currents.
[Illustration: FIG. 10.]
The simplest form of a synchronous motor is obtained by winding a
laminated ring provided with pole projections with four coils, and
connecting the same in the manner before indicated. An iron disc having
a segment cut away on each side may be used as an armature. Such a motor
is shown in Fig. 9. The disc being arranged to rotate freely within the
ring in close proximity to the projections, it is evident that as the
poles are shifted it will, owing to its tendency to place itself in such
a position as to embrace the greatest number of the lines of force,
closely follow the movement of the poles, and its motion will be
synchronous with that of the armature of the generator; that is, in the
peculiar disposition shown in Fig. 9, in which the armature produces by
one revolution two current impulses in each of the circuits. It is
evident that if, by one revolution of the armature, a greater number of
impulses is produced, the speed of the motor will be correspondingly
increased. Considering that the attraction exerted upon the disc is
greatest when the same is in close proximity to the poles, it follows
that such a motor will maintain exactly the same speed at all loads
within the limits of its capacity.
To facilitate the starting, the disc may be provided with a coil closed
upon itself. The advantage secured by such a coil is evident. On the
start the currents set up in the coil strongly energize the disc and
increase the attraction exerted upon the same by the ring, and currents
being generated in the coil as long as the speed of the armature is
inferior to that of the poles, considerable work may be performed by
such a motor even if the speed be below normal. The intensity of the
poles being constant, no currents will be generated in the coil when the
motor is turning at its normal speed.
Instead of closing the coil upon itself, its ends may be connected to
two insulated sliding rings, and a continuous current supplied to these
from a suitable generator. The proper way to start such a motor is to
close the coil upon itself until the normal speed is reached, or nearly
so, and then turn on the continuous current. If the disc be very
strongly energized by a continuous current the motor may not be able to
start, but if it be weakly energized, or generally so that the
magnetizing effect of the ring is preponderating, it will start and
reach the normal speed. Such a motor will maintain absolutely the same
speed at all loads. It has also been found that if the motive power of
the generator is not excessive, by checking the motor the speed of the
generator is diminished in synchronism with that of the motor. It is
characteristic of this form of motor that it cannot be reversed by
reversing the continuous current through the coil.
[Illustration: FIG. 11.]
[Illustration: FIG. 12.]
The synchronism of these motors may be demonstrated experimentally in a
variety of ways. For this purpose it is best to employ a motor
consisting of a stationary field magnet and an armature arranged to
rotate within the same, as indicated in Fig. 13. In this case the
shifting of the poles of the armature produces a rotation of the latter
in the opposite direction. It results therefrom that when the normal
speed is reached, the poles of the armature assume fixed positions
relatively to the field magnet, and the same is magnetized by
induction, exhibiting a distinct pole on each of the pole-pieces. If a
piece of soft iron is approached to the field magnet, it will at the
start be attracted with a rapid vibrating motion produced by the
reversals of polarity of the magnet, but as the speed of the armature
increases, the vibrations become less and less frequent and finally
entirely cease. Then the iron is weakly but permanently attracted,
showing that synchronism is reached and the field magnet energized by
induction.
The disc may also be used for the experiment. If held quite close to the
armature it will turn as long as the speed of rotation of the poles
exceeds that of the armature; but when the normal speed is reached, or
very nearly so, it ceases to rotate and is permanently attracted.
[Illustration: FIG. 13.]
A crude but illustrative experiment is made with an incandescent lamp.
Placing the lamp in circuit with the continuous current generator and in
series with the magnet coil, rapid fluctuations are observed in the
light in consequence of the induced currents set up in the coil at the
start; the speed increasing, the fluctuations occur at longer intervals,
until they entirely disappear, showing that the motor has attained its
normal speed. A telephone receiver affords a most sensitive instrument;
when connected to any circuit in the motor the synchronism may be easily
detected on the disappearance of the induced currents.
In motors of the synchronous type it is desirable to maintain the
quantity of the shifting magnetism constant, especially if the magnets
are not properly subdivided.
To obtain a rotary effort in these motors was the subject of long
thought. In order to secure this result it was necessary to make such a
disposition that while the poles of one element of the motor are shifted
by the alternate currents of the source, the poles produced upon the
other elements should always be maintained in the proper relation to the
former, irrespective of the speed of the motor. Such a condition exists
in a continuous current motor; but in a synchronous motor, such as
described, this condition is fulfilled only when the speed is normal.
[Illustration: FIG. 14.]
The object has been attained by placing within the ring a properly
subdivided cylindrical iron core wound with several independent coils
closed upon themselves. Two coils at right angles as in Fig. 14, are
sufficient, but a greater number may be advantageously employed. It
results from this disposition that when the poles of the ring are
shifted, currents are generated in the closed armature coils. These
currents are the most intense at or near the points of the greatest
density of the lines of force, and their effect is to produce poles upon
the armature at right angles to those of the ring, at least
theoretically so; and since this action is entirely independent of the
speed--that is, as far as the location of the poles is concerned--a
continuous pull is exerted upon the periphery of the armature. In many
respects these motors are similar to the continuous current motors. If
load is put on, the speed, and also the resistance of the motor, is
diminished and more current is made to pass through the energizing
coils, thus increasing the effort. Upon the load being taken off, the
counter-electromotive force increases and less current passes through
the primary or energizing coils. Without any load the speed is very
nearly equal to that of the shifting poles of the field magnet.
[Illustration: FIG. 15.]
[Illustration: FIG. 16.]
[Illustration: FIG. 17.]
It will be found that the rotary effort in these motors fully equals
that of the continuous current motors. The effort seems to be greatest
when both armature and field magnet are without any projections; but as
in such dispositions the field cannot be concentrated, probably the best
results will be obtained by leaving pole projections on one of the
elements only. Generally, it may be stated the projections diminish the
torque and produce a tendency to synchronism.
A characteristic feature of motors of this kind is their property of
being very rapidly reversed. This follows from the peculiar action of
the motor. Suppose the armature to be rotating and the direction of
rotation of the poles to be reversed. The apparatus then represents a
dynamo machine, the power to drive this machine being the momentum
stored up in the armature and its speed being the sum of the speeds of
the armature and the poles.
[Illustration: FIG. 18.]
[Illustration: FIG. 19.]
[Illustration: FIG. 20.]
[Illustration: FIG. 21.]
If we now consider that the power to drive such a dynamo would be very
nearly proportional to the third power of the speed, for that reason
alone the armature should be quickly reversed. But simultaneously with
the reversal another element is brought into action, namely, as the
movement of the poles with respect to the armature is reversed, the
motor acts like a transformer in which the resistance of the secondary
circuit would be abnormally diminished by producing in this circuit an
additional electromotive force. Owing to these causes the reversal is
instantaneous.
If it is desirable to secure a constant speed, and at the same time a
certain effort at the start, this result may be easily attained in a
variety of ways. For instance, two armatures, one for torque and the
other for synchronism, may be fastened on the same shaft and any desired
preponderance may be given to either one, or an armature may be wound
for rotary effort, but a more or less pronounced tendency to synchronism
may be given to it by properly constructing the iron core; and in many
other ways.
As a means of obtaining the required phase of the currents in both the
circuits, the disposition of the two coils at right angles is the
simplest, securing the most uniform action; but the phase may be
obtained in many other ways, varying with the machine employed. Any of
the dynamos at present in use may be easily adapted for this purpose by
making connections to proper points of the generating coils. In closed
circuit armatures, such as used in the continuous current systems, it is
best to make four derivations from equi-distant points or bars of the
commutator, and to connect the same to four insulated sliding rings on
the shaft. In this case each of the motor circuits is connected to two
diametrically opposite bars of the commutator. In such a disposition the
motor may also be operated at half the potential and on the three-wire
plan, by connecting the motor circuits in the proper order to three of
the contact rings.
In multipolar dynamo machines, such as used in the converter systems,
the phase is conveniently obtained by winding upon the armature two
series of coils in such a manner that while the coils of one set or
series are at their maximum production of current, the coils of the
other will be at their neutral position, or nearly so, whereby both sets
of coils may be subjected simultaneously or successively to the inducing
action of the field magnets.
Generally the circuits in the motor will be similarly disposed, and
various arrangements may be made to fulfill the requirements; but the
simplest and most practicable is to arrange primary circuits on
stationary parts of the motor, thereby obviating, at least in certain
forms, the employment of sliding contacts. In such a case the magnet
coils are connected alternately in both the circuits; that is, 1, 3,
5 ... in one, and 2, 4, 6 ... in the other, and the coils of each set
of series may be connected all in the same manner, or alternately in
opposition; in the latter case a motor with half the number of poles
will result, and its action will be correspondingly modified. The Figs.
15, 16, and 17, show three different phases, the magnet coils in each
circuit being connected alternately in opposition. In this case there
will be always four poles, as in Figs. 15 and 17; four pole projections
will be neutral; and in Fig. 16 two adjacent pole projections will have
the same polarity. If the coils are connected in the same manner there
will be eight alternating poles, as indicated by the letters n' s'
in Fig. 15.
The employment of multipolar motors secures in this system an advantage
much desired and unattainable in the continuous current system, and that
is, that a motor may be made to run exactly at a predetermined speed
irrespective of imperfections in construction, of the load, and, within
certain limits, of electromotive force and current strength.
In a general distribution system of this kind the following plan should
be adopted. At the central station of supply a generator should be
provided having a considerable number of poles. The motors operated from
this generator should be of the synchronous type, but possessing
sufficient rotary effort to insure their starting. With the observance
of proper rules of construction it may be admitted that the speed of
each motor will be in some inverse proportion to its size, and the
number of poles should be chosen accordingly. Still, exceptional demands
may modify this rule. In view of this, it will be advantageous to
provide each motor with a greater number of pole projections or coils,
the number being preferably a multiple of two and three. By this means,
by simply changing the connections of the coils, the motor may be
adapted to any probable demands.
If the number of the poles in the motor is even, the action will be
harmonious and the proper result will be obtained; if this is not the
case, the best plan to be followed is to make a motor with a double
number of poles and connect the same in the manner before indicated, so
that half the number of poles result. Suppose, for instance, that the
generator has twelve poles, and it would be desired to obtain a speed
equal to 12/7 of the speed of the generator. This would require a motor
with seven pole projections or magnets, and such a motor could not be
properly connected in the circuits unless fourteen armature coils would
be provided, which would necessitate the employment of sliding
contacts. To avoid this, the motor should be provided with fourteen
magnets and seven connected in each circuit, the magnets in each circuit
alternating among themselves. The armature should have fourteen closed
coils. The action of the motor will not be quite as perfect as in the
case of an even number of poles, but the drawback will not be of a
serious nature.
However, the disadvantages resulting from this unsymmetrical form will
be reduced in the same proportion as the number of the poles is
augmented.
If the generator has, say, n, and the motor n_{1} poles, the speed of
the motor will be equal to that of the generator multiplied by n/n_{1}.
The speed of the motor will generally be dependent on the number of the
poles, but there may be exceptions to this rule. The speed may be
modified by the phase of the currents in the circuit or by the character
of the current impulses or by intervals between each or between groups
of impulses. Some of the possible cases are indicated in the diagrams,
Figs. 18, 19, 20 and 21, which are self-explanatory. Fig. 18 represents
the condition generally existing, and which secures the best result. In
such a case, if the typical form of motor illustrated in Fig. 9 is
employed, one complete wave in each circuit will produce one revolution
of the motor. In Fig. 19 the same result will be effected by one wave in
each circuit, the impulses being successive; in Fig. 20 by four, and in
Fig. 21 by eight waves.
By such means any desired speed may be attained, that is, at least
within the limits of practical demands. This system possesses this
advantage, besides others, resulting from simplicity. At full loads the
motors show an efficiency fully equal to that of the continuous current
motors. The transformers present an additional advantage in their
capability of operating motors. They are capable of similar
modifications in construction, and will facilitate the introduction of
motors and their adaptation to practical demands. Their efficiency
should be higher than that of the present transformers, and I base my
assertion on the following:
In a transformer, as constructed at present, we produce the currents in
the secondary circuit by varying the strength of the primary or exciting
currents. If we admit proportionality with respect to the iron core the
inductive effect exerted upon the secondary coil will be proportional
to the numerical sum of the variations in the strength of the exciting
current per unit of time; whence it follows that for a given variation
any prolongation of the primary current will result in a proportional
loss. In order to obtain rapid variations in the strength of the
current, essential to efficient induction, a great number of undulations
are employed; from this practice various disadvantages result. These
are: Increased cost and diminished efficiency of the generator; more
waste of energy in heating the cores, and also diminished output of the
transformer, since the core is not properly utilized, the reversals
being too rapid. The inductive effect is also very small in certain
phases, as will be apparent from a graphic representation, and there may
be periods of inaction, if there are intervals between the succeeding
current impulses or waves. In producing a shifting of the poles in a
transformer, and thereby inducing currents, the induction is of the
ideal character, being always maintained at its maximum action. It is
also reasonable to assume that by a shifting of the poles less energy
will be wasted than by reversals.
CHAPTER IV.
MODIFICATIONS AND EXPANSIONS OF THE TESLA POLYPHASE SYSTEMS.
In his earlier papers and patents relative to polyphase currents, Mr.
Tesla devoted himself chiefly to an enunciation of the broad lines and
ideas lying at the basis of this new work; but he supplemented this
immediately by a series of other striking inventions which may be
regarded as modifications and expansions of certain features of the
Tesla systems. These we shall now proceed to deal with.
In the preceding chapters we have thus shown and described the Tesla
electrical systems for the transmission of power and the conversion and
distribution of electrical energy, in which the motors and the
transformers contain two or more coils or sets of coils, which were
connected up in independent circuits with corresponding coils of an
alternating current generator, the operation of the system being brought
about by the co-operation of the alternating currents in the independent
circuits in progressively moving or shifting the poles or points of
maximum magnetic effect of the motors or converters. In these systems
two independent conductors are employed for each of the independent
circuits connecting the generator with the devices for converting the
transmitted currents into mechanical energy or into electric currents of
another character. This, however, is not always necessary. The two or
more circuits may have a single return path or wire in common, with a
loss, if any, which is so extremely slight that it may be disregarded
entirely. For the sake of illustration, if the generator have two
independent coils and the motor two coils or two sets of coils in
corresponding relations to its operative elements one terminal of each
generator coil is connected to the corresponding terminals of the motor
coils through two independent conductors, while the opposite terminals
of the respective coils are both connected to one return wire. The
following description deals with the modification. Fig. 22 is a
diagrammatic illustration of a generator and single motor constructed
and electrically connected in accordance with the invention. Fig. 23 is
a diagram of the system as it is used in operating motors or converters,
or both, in parallel, while Fig. 24 illustrates diagrammatically the
manner of operating two or more motors or converters, or both, in
series. Referring to Fig. 22, A A designate the poles of the field
magnets of an alternating-current generator, the armature of which,
being in this case cylindrical in form and mounted on a shaft, C, is
wound longitudinally with coils B B'. The shaft C carries three
insulated contact-rings, _a b c_, to two of which, as _b c_, one
terminal of each coil, as _e d_, is connected. The remaining terminals,
_f g_, are both connected to the third ring, _a_.
[Illustration: FIG. 22.]
[Illustration: FIG. 24.]
A motor in this case is shown as composed of a ring, H, wound with four
coils, I I J J, electrically connected, so as to co-operate in pairs,
with a tendency to fix the poles of the ring at four points ninety
degrees apart. Within the magnetic ring H is a disc or cylindrical core
wound with two coils, G G', which may be connected to form two closed
circuits. The terminals _j k_ of the two sets or pairs of coils are
connected, respectively, to the binding-posts E' F', and the other
terminals, _h i_, are connected to a single binding-post, D'. To operate
the motor, three line-wires are used to connect the terminals of the
generator with those of the motor.
[Illustration: FIG. 23.]
So far as the apparent action or mode of operation of this arrangement
is concerned, the single wire D, which is, so to speak, a common
return-wire for both circuits, may be regarded as two independent wires.
In the illustration, with the order of connection shown, coil B' of the
generator is producing its maximum current and coil B its minimum; hence
the current which passes through wire e, ring b, brush b', line-wire E,
terminal E', wire j, coils I I, wire or terminal D', line-wire D, brush
_a'_, ring _a_, and wire _f_, fixes the polar line of the motor midway
between the two coils I I; but as the coil B' moves from the position
indicated it generates less current, while coil B, moving into the
field, generates more. The current from coil B passes through the
devices and wires designated by the letters _d_, _c_, C' F, F' _k_, J J,
_i_, D', D, _a'_, _a_, and _g_, and the position of the poles of the
motor will be due to the resultant effect of the currents in the two
sets of coils--that is, it will be advanced in proportion to the advance
or forward movement of the armature coils. The movement of the
generator-armature through one-quarter of a revolution will obviously
bring coil B' into its neutral position and coil B into its position of
maximum effect, and this shifts the poles ninety degrees, as they are
fixed solely by coils B. This action is repeated for each quarter of a
complete revolution.
When more than one motor or other device is employed, they may be run
either in parallel or series. In Fig. 23 the former arrangement is
shown. The electrical device is shown as a converter, L, of which the
two sets of primary coils _p r_ are connected, respectively, to the
mains F E, which are electrically connected with the two coils of the
generator. The cross-circuit wires _l m_, making these connections, are
then connected to the common return-wire D. The secondary coils _p' p''_
are in circuits _n o_, including, for example, incandescent lamps. Only
one converter is shown entire in this figure, the others being
illustrated diagrammatically.
When motors or converters are to be run in series, the two wires E F are
led from the generator to the coils of the first motor or converter,
then continued on to the next, and so on through the whole series, and
are then joined to the single wire D, which completes both circuits
through the generator. This is shown in Fig. 24, in which J I represent
the two coils or sets of coils of the motors.
There are, of course, other conditions under which the same idea may be
carried out. For example, in case the motor and generator each has three
independent circuits, one terminal of each circuit is connected to a
line-wire, and the other three terminals to a common return-conductor.
This arrangement will secure similar results to those attained with a
generator and motor having but two independent circuits, as above
described.
When applied to such machines and motors as have three or more induced
circuits with a common electrical joint, the three or more terminals of
the generator would be simply connected to those of the motor. Mr.
Tesla states, however, that the results obtained in this manner show a
lower efficiency than do the forms dwelt upon more fully above.
CHAPTER V.
UTILIZING FAMILIAR TYPES OF GENERATOR OF THE CONTINUOUS CURRENT TYPE.
The preceding descriptions have assumed the use of alternating current
generators in which, in order to produce the progressive movement of the
magnetic poles, or of the resultant attraction of independent field
magnets, the current generating coils are independent or separate. The
ordinary forms of continuous current dynamos may, however, be employed
for the same work, in accordance with a method of adaptation devised by
Mr. Tesla. As will be seen, the modification involves but slight changes
in their construction, and presents other elements of economy.
On the shaft of a given generator, either in place of or in addition to
the regular commutator, are secured as many pairs of insulated
collecting-rings as there are circuits to be operated. Now, it will be
understood that in the operation of any dynamo electric generator the
currents in the coils in their movement through the field of force
undergo different phases--that is to say, at different positions of the
coils the currents have certain directions and certain strengths--and
that in the Tesla motors or transformers it is necessary that the
currents in the energizing coils should undergo a certain order of
variations in strength and direction. Hence, the further step--viz., the
connection between the induced or generating coils of the machine and
the contact-rings from which the currents are to be taken off--will be
determined solely by what order of variations of strength and direction
in the currents is desired for producing a given result in the
electrical translating device. This may be accomplished in various ways;
but in the drawings we give typical instances only of the best and most
practicable ways of applying the invention to three of the leading types
of machines in widespread use, in order to illustrate the principle.
Fig. 25 is a diagram illustrative of the mode of applying the invention
to the well-known type of "closed" or continuous circuit machines. Fig.
26 is a similar diagram embodying an armature with separate coils
connected diametrically, or what is generally called an "open-circuit"
machine. Fig. 27 is a diagram showing the application of the invention
to a machine the armature-coils of which have a common joint.
[Illustration: FIG. 25.]
Referring to Fig. 25, let A represent a Tesla motor or transformer
which, for convenience, we will designate as a "converter." It consists
of an annular core, B, wound with four independent coils, C and D, those
diametrically opposite being connected together so as to co-operate in
pairs in establishing free poles in the ring, the tendency of each pair
being to fix the poles at ninety degrees from the other. There may be an
armature, E, within the ring, which is wound with coils closed upon
themselves. The object is to pass through coils C D currents of such
relative strength and direction as to produce a progressive shifting or
movement of the points of maximum magnetic effect around the ring, and
to thereby maintain a rotary movement of the armature. There are
therefore secured to the shaft F of the generator, four insulated
contact-rings, _a b c d_, upon which bear the collecting-brushes
_a' b' c' d'_, connected by wires G G H H, respectively, with the
terminals of coils C and D.
Assume, for sake of illustration, that the coils D D are to receive the
maximum and coils C C at the same instant the minimum current, so that
the polar line may be midway between the coils D D. The rings _a b_
would therefore be connected to the continuous armature-coil at its
neutral points with respect to the field, or the point corresponding
with that of the ordinary commutator brushes, and between which exists
the greatest difference of potential; while rings _c d_ would be
connected to two points in the coil, between which exists no difference
of potential. The best results will be obtained by making these
connections at points equidistant from one another, as shown. These
connections are easiest made by using wires L between the rings and the
loops or wires J, connecting the coil I to the segments of the
commutator K. When the converters are made in this manner, it is evident
that the phases of the currents in the sections of the generator coil
will be reproduced in the converter coils. For example, after turning
through an arc of ninety degrees the conductors L L, which before
conveyed the maximum current, will receive the minimum current by reason
of the change in the position of their coils, and it is evident that for
the same reason the current in these coils has gradually fallen from the
maximum to the minimum in passing through the arc of ninety degrees. In
this special plan of connections, the rotation of the magnetic poles of
the converter will be synchronous with that of the armature coils of the
generator, and the result will be the same, whether the energizing
circuits are derivations from a continuous armature coil or from
independent coils, as in Mr. Tesla's other devices.
In Fig. 25, the brushes M M are shown in dotted lines in their proper
normal position. In practice these brushes may be removed from the
commutator and the field of the generator excited by an external source
of current; or the brushes may be allowed to remain on the commutator
and to take off a converted current to excite the field, or to be used
for other purposes.
In a certain well-known class of machines known as the "open circuit,"
the armature contains a number of coils the terminals of which connect
to commutator segments, the coils being connected across the armature in
pairs. This type of machine is represented in Fig. 26. In this machine
each pair of coils goes through the same phases as the coils in some of
the generators already shown, and it is obviously only necessary to
utilize them in pairs or sets to operate a Tesla converter by extending
the segments of the commutators belonging to each pair of coils and
causing a collecting brush to bear on the continuous portion of each
segment. In this way two or more circuits may be taken off from the
generator, each including one or more pairs or sets of coils as may be
desired.
[Illustration: FIG. 26.]
[Illustration: FIG. 27.]
In Fig. 26 I I represent the armature coils, T T the poles of the field
magnet, and F the shaft carrying the commutators, which are extended to
form continuous portions _a b c d_. The brushes bearing on the
continuous portions for taking off the alternating currents are
represented by _a' b' c' d'_. The collecting brushes, or those which may
be used to take off the direct current, are designated by M M. Two pairs
of the armature coils and their commutators are shown in the figure as
being utilized; but all may be utilized in a similar manner.
There is another well-known type of machine in which three or more
coils, A' B' C', on the armature have a common joint, the free ends
being connected to the segments of a commutator. This form of generator
is illustrated in Fig. 27. In this case each terminal of the generator
is connected directly or in derivation to a continuous ring, _a b c_,
and collecting brushes, _a' b' c'_, bearing thereon, take off the
alternating currents that operate the motor. It is preferable in this
case to employ a motor or transformer with three energizing coils, A''
B'' C'', placed symmetrically with those of the generator, and the
circuits from the latter are connected to the terminals of such coils
either directly--as when they are stationary--or by means of brushes
_e'_ and contact rings _e_. In this, as in the other cases, the ordinary
commutator may be used on the generator, and the current taken from it
utilized for exciting the generator field-magnets or for other
purposes.
CHAPTER VI.
METHOD OF OBTAINING DESIRED SPEED OF MOTOR OR GENERATOR.
With the object of obtaining the desired speed in motors operated by
means of alternating currents of differing phase, Mr. Tesla has devised
various plans intended to meet the practical requirements of the case,
in adapting his system to types of multipolar alternating current
machines yielding a large number of current reversals for each
revolution.
For example, Mr. Tesla has pointed out that to adapt a given type of
alternating current generator, you may couple rigidly two complete
machines, securing them together in such a way that the requisite
difference in phase will be produced; or you may fasten two armatures to
the same shaft within the influence of the same field and with the
requisite angular displacement to yield the proper difference in phase
between the two currents; or two armatures may be attached to the same
shaft with their coils symmetrically disposed, but subject to the
influence of two sets of field magnets duly displaced; or the two sets
of coils may be wound on the same armature alternately or in such manner
that they will develop currents the phases of which differ in time
sufficiently to produce the rotation of the motor.
Another method included in the scope of the same idea, whereby a single
generator may run a number of motors either at its own rate of speed or
all at different speeds, is to construct the motors with fewer poles
than the generator, in which case their speed will be greater than that
of the generator, the rate of speed being higher as the number of their
poles is relatively less. This may be understood from an example, taking
a generator that has two independent generating coils which revolve
between two pole pieces oppositely magnetized; and a motor with
energizing coils that produce at any given time two magnetic poles in
one element that tend to set up a rotation of the motor. A generator
thus constructed yields four reversals, or impulses, in each
revolution, two in each of its independent circuits; and the effect upon
the motor is to shift the magnetic poles through three hundred and sixty
degrees. It is obvious that if the four reversals in the same order
could be produced by each half-revolution of the generator the motor
would make two revolutions to the generator's one. This would be readily
accomplished by adding two intermediate poles to the generator or
altering it in any of the other equivalent ways above indicated. The
same rule applies to generators and motors with multiple poles. For
instance, if a generator be constructed with two circuits, each of which
produces twelve reversals of current to a revolution, and these currents
be directed through the independent energizing-coils of a motor, the
coils of which are so applied as to produce twelve magnetic poles at all
times, the rotation of the two will be synchronous; but if the
motor-coils produce but six poles, the movable element will be rotated
twice while the generator rotates once; or if the motor have four poles,
its rotation will be three times as fast as that of the generator.
[Illustration: FIG. 28.]
[Illustration: FIG. 29.]
These features, so far as necessary to an understanding of the
principle, are here illustrated. Fig. 28 is a diagrammatic illustration
of a generator constructed in accordance with the invention. Fig. 29 is
a similar view of a correspondingly constructed motor. Fig. 30 is a
diagram of a generator of modified construction. Fig. 31 is a diagram of
a motor of corresponding character. Fig. 32 is a diagram of a system
containing a generator and several motors adapted to run at various
speeds.
In Fig. 28, let C represent a cylindrical armature core wound
longitudinally with insulated coils A A, which are connected up in
series, the terminals of the series being connected to collecting-rings
_a a_ on the shaft G. By means of this shaft the armature is mounted to
rotate between the poles of an annular field-magnet D, formed with polar
projections wound with coils E, that magnetize the said projections. The
coils E are included in the circuit of a generator F, by means of which
the field-magnet is energized. If thus constructed, the machine is a
well-known form of alternating-current generator. To adapt it to his
system, however, Mr. Tesla winds on armature C a second set of coils B B
intermediate to the first, or, in other words, in such positions that
while the coils of one set are in the relative positions to the poles of
the field-magnet to produce the maximum current, those of the other set
will be in the position in which they produce the minimum current. The
coils B are connected, also, in series and to two connecting-rings,
secured generally to the shaft at the opposite end of the armature.
[Illustration: FIG. 30.]
[Illustration: FIG. 31.]
The motor shown in Fig. 29 has an annular field-magnet H, with four
pole-pieces wound with coils I. The armature is constructed similarly to
the generator, but with two sets of two coils in closed circuits to
correspond with the reduced number of magnetic poles in the field. From
the foregoing it is evident that one revolution of the armature of the
generator producing eight current impulses in each circuit will produce
two revolutions of the motor-armature.
The application of the principle of this invention is not, however,
confined to any particular form of machine. In Figs. 30 and 31 a
generator and motor of another well-known type are shown. In Fig. 30, J
J are magnets disposed in a circle and wound with coils K, which are in
circuit with a generator which supplies the current that maintains the
field of force. In the usual construction of these machines the
armature-conductor L is carried by a suitable frame, so as to be rotated
in face of the magnets J J, or between these magnets and another similar
set in front of them. The magnets are energized so as to be of
alternately opposite polarity throughout the series, so that as the
conductor C is rotated the current impulses combine or are added to one
another, those produced by the conductor in any given position being all
in the same direction. To adapt such a machine to his system, Mr. Tesla
adds a second set of induced conductors M, in all respects similar to
the first, but so placed in reference to it that the currents produced
in each will differ by a quarter-phase. With such relations it is
evident that as the current decreases in conductor L it increases in
conductor M, and conversely, and that any of the forms of Tesla motor
invented for use in this system may be operated by such a generator.
Fig. 31 is intended to show a motor corresponding to the machine in Fig.
30. The construction of the motor is identical with that of the
generator, and if coupled thereto it will run synchronously therewith.
J' J' are the field-magnets, and K' the coils thereon. L' is one of the
armature-conductors and M' the other.
Fig. 32 shows in diagram other forms of machine. The generator N in this
case is shown as consisting of a stationary ring O, wound with
twenty-four coils P P', alternate coils being connected in series in two
circuits. Within this ring is a disc or drum Q, with projections Q'
wound with energizing-coils included in circuit with a generator R. By
driving this disc or cylinder alternating currents are produced in the
coils P and P', which are carried off to run the several motors.
The motors are composed of a ring or annular field-magnet S, wound with
two sets of energizing-coils T T', and armatures U, having projections
U' wound with coils V, all connected in series in a closed circuit or
each closed independently on itself.
Suppose the twelve generator-coils P are wound alternately in opposite
directions, so that any two adjacent coils of the same set tend to
produce a free pole in the ring O between them and the twelve coils P'
to be similarly wound. A single revolution of the disc or cylinder Q,
the twelve polar projections of which are of opposite polarity, will
therefore produce twelve current impulses in each of the circuits W W'.
Hence the motor X, which has sixteen coils or eight free poles, will
make one and a half turns to the generator's one. The motor Y, with
twelve coils or six poles, will rotate with twice the speed of the
generator, and the motor Z, with eight coils or four poles, will revolve
three times as fast as the generator. These multipolar motors have a
peculiarity which may be often utilized to great advantage. For example,
in the motor X, Fig. 32, the eight poles may be either alternately
opposite or there may be at any given time alternately two like and two
opposite poles. This is readily attained by making the proper electrical
connections. The effect of such a change, however, would be the same as
reducing the number of poles one-half, and thereby doubling the speed
of any given motor.
[Illustration: FIG. 32.]
It is obvious that the Tesla electrical transformers which have
independent primary currents may be used with the generators described.
It may also be stated with respect to the devices we now describe that
the most perfect and harmonious action of the generators and motors is
obtained when the numbers of the poles of each are even and not odd. If
this is not the case, there will be a certain unevenness of action which
is the less appreciable as the number of poles is greater; although this
may be in a measure corrected by special provisions which it is not here
necessary to explain. It also follows, as a matter of course, that if
the number of the poles of the motor be greater than that of the
generator the motor will revolve at a slower speed than the generator.
In this chapter, we may include a method devised by Mr. Tesla for
avoiding the very high speeds which would be necessary with large
generators. In lieu of revolving the generator armature at a high rate
of speed, he secures the desired result by a rotation of the magnetic
poles of one element of the generator, while driving the other at a
different speed. The effect is the same as that yielded by a very high
rate of rotation.
In this instance, the generator which supplies the current for operating
the motors or transformers consists of a subdivided ring or annular core
wound with four diametrically-opposite coils, E E', Fig. 33. Within the
ring is mounted a cylindrical armature-core wound longitudinally with
two independent coils, F F', the ends of which lead, respectively, to
two pairs of insulated contact or collecting rings, D D' G G', on the
armature shaft. Collecting brushes _d d' g g'_ bear upon these rings,
respectively, and convey the currents through the two independent
line-circuits M M'. In the main line there may be included one or more
motors or transformers, or both. If motors be used, they are of the
usual form of Tesla construction with independent coils or sets of coils
J J', included, respectively, in the circuits M M'. These
energizing-coils are wound on a ring or annular field or on pole pieces
thereon, and produce by the action of the alternating currents passing
through them a progressive shifting of the magnetism from pole to pole.
The cylindrical armature H of the motor is wound with two coils at right
angles, which form independent closed circuits.
If transformers be employed, one set of the primary coils, as N N, wound
on a ring or annular core is connected to one circuit, as M', and the
other primary coils, N N', to the circuit M. The secondary coils K K'
may then be utilized for running groups of incandescent lamps P P'.
[Illustration: FIG. 33.]
With this generator an exciter is employed. This consists of two poles,
A A, of steel permanently magnetized, or of iron excited by a battery or
other generator of continuous currents, and a cylindrical armature core
mounted on a shaft, B, and wound with two longitudinal coils, C C'. One
end of each of these coils is connected to the collecting-rings _b c_,
respectively, while the other ends are both connected to a ring, _a_.
Collecting-brushes _b' c'_ bear on the rings _b c_, respectively, and
conductors L L convey the currents therefrom through the coils E and E
of the generator. L' is a common return-wire to brush _a'_. Two
independent circuits are thus formed, one including coils C of the
exciter and E E of the generator, the other coils C' of the exciter and
E' E' of the generator. It results from this that the operation of the
exciter produces a progressive movement of the magnetic poles of the
annular field-core of the generator, the shifting or rotary movement of
the poles being synchronous with the rotation of the exciter armature.
Considering the operative conditions of a system thus established, it
will be found that when the exciter is driven so as to energize the
field of the generator, the armature of the latter, if left free to
turn, would rotate at a speed practically the same as that of the
exciter. If under such conditions the coils F F' of the generator
armature be closed upon themselves or short-circuited, no currents, at
least theoretically, will be generated in these armature coils. In
practice the presence of slight currents is observed, the existence of
which is attributable to more or less pronounced fluctuations in the
intensity of the magnetic poles of the generator ring. So, if the
armature-coils F F' be closed through the motor, the latter will not be
turned as long as the movement of the generator armature is synchronous
with that of the exciter or of the magnetic poles of its field. If, on
the contrary, the speed of the generator armature be in any way checked,
so that the shifting or rotation of the poles of the field becomes
relatively more rapid, currents will be induced in the armature coils.
This obviously follows from the passing of the lines of force across the
armature conductors. The greater the speed of rotation of the magnetic
poles relatively to that of the armature the more rapidly the currents
developed in the coils of the latter will follow one another, and the
more rapidly the motor will revolve in response thereto, and this
continues until the armature generator is stopped entirely, as by a
brake, when the motor, if properly constructed, runs at the speed with
which the magnetic poles of the generator rotate.
The effective strength of the currents developed in the armature coils
of the generator is dependent upon the strength of the currents
energizing the generator and upon the number of rotations per unit of
time of the magnetic poles of the generator; hence the speed of the
motor armature will depend in all cases upon the relative speeds of the
armature of the generator and of its magnetic poles. For example, if the
poles are turned two thousand times per unit of time and the armature is
turned eight hundred, the motor will turn twelve hundred times, or
nearly so. Very slight differences of speed may be indicated by a
delicately balanced motor.
Let it now be assumed that power is applied to the generator armature to
turn it in a direction opposite to that in which its magnetic poles
rotate. In such case the result would be similar to that produced by a
generator the armature and field magnets of which are rotated in
opposite directions, and by reason of these conditions the motor
armature will turn at a rate of speed equal to the sum of the speeds of
the armature and magnetic poles of the generator, so that a
comparatively low speed of the generator armature will produce a high
speed in the motor.
It will be observed in connection with this system that on diminishing
the resistance of the external circuit of the generator armature by
checking the speed of the motor or by adding translating devices in
multiple arc in the secondary circuit or circuits of the transformer the
strength of the current in the armature circuit is greatly increased.
This is due to two causes: first, to the great differences in the speeds
of the motor and generator, and, secondly, to the fact that the
apparatus follows the analogy of a transformer, for, in proportion as
the resistance of the armature or secondary circuits is reduced, the
strength of the currents in the field or primary circuits of the
generator is increased and the currents in the armature are augmented
correspondingly. For similar reasons the currents in the armature-coils
of the generator increase very rapidly when the speed of the armature is
reduced when running in the same direction as the magnetic poles or
conversely.
It will be understood from the above description that the
generator-armature may be run in the direction of the shifting of the
magnetic poles, but more rapidly, and that in such case the speed of the
motor will be equal to the difference between the two rates.
CHAPTER VII.
REGULATOR FOR ROTARY CURRENT MOTORS.
An interesting device for regulating and reversing has been devised by
Mr. Tesla for the purpose of varying the speed of polyphase motors. It
consists of a form of converter or transformer with one element capable
of movement with respect to the other, whereby the inductive relations
may be altered, either manually or automatically, for the purpose of
varying the strength of the induced current. Mr. Tesla prefers to
construct this device in such manner that the induced or secondary
element may be movable with respect to the other; and the invention, so
far as relates merely to the construction of the device itself,
consists, essentially, in the combination, with two opposite magnetic
poles, of an armature wound with an insulated coil and mounted on a
shaft, whereby it may be turned to the desired extent within the field
produced by the poles. The normal position of the core of the secondary
element is that in which it most completely closes the magnetic circuit
between the poles of the primary element, and in this position its coil
is in its most effective position for the inductive action upon it of
the primary coils; but by turning the movable core to either side, the
induced currents delivered by its coil become weaker until, by a
movement of the said core and coil through 90 deg., there will be no current
delivered.
Fig. 34 is a view in side elevation of the regulator. Fig. 35 is a
broken section on line _x x_ of Fig. 34. Fig. 36 is a diagram
illustrating the most convenient manner of applying the regulator to
ordinary forms of motors, and Fig. 37 is a similar diagram illustrating
the application of the device to the Tesla alternating-current motors.
The regulator may be constructed in many ways to secure the desired
result; but that which is, perhaps, its best form is shown in Figs. 34
and 35.
A represents a frame of iron. B B are the cores of the inducing or
primary coils C C. D is a shaft mounted on the side bars, D', and on
which is secured a sectional iron core, E, wound with an induced or
secondary coil, F, the convolutions of which are parallel with the axis
of the shaft. The ends of the core are rounded off so as to fit closely
in the space between the two poles and permit the core E to be turned to
and held at any desired point. A handle, G, secured to the projecting
end of the shaft D, is provided for this purpose.
[Illustration: FIG. 34.]
[Illustration: FIG. 35.]
In Fig. 36 let H represent an ordinary alternating current generator,
the field-magnets of which are excited by a suitable source of current,
I. Let J designate an ordinary form of electromagnetic motor provided
with an armature, K, commutator L, and field-magnets M. It is well known
that such a motor, if its field-magnet cores be divided up into
insulated sections, may be practically operated by an alternating
current; but in using this regulator with such a motor, Mr. Tesla
includes one element of the motor only--say the armature-coils--in the
main circuit of the generator, making the connections through the
brushes and the commutator in the usual way. He also includes one of the
elements of the regulator--say the stationary coils--in the same
circuit, and in the circuit with the secondary or movable coil of the
regulator he connects up the field-coils of the motor. He also prefers
to use flexible conductors to make the connections from the secondary
coil of the regulator, as he thereby avoids the use of sliding contacts
or rings without interfering with the requisite movement of the core E.
If the regulator be in its normal position, or that in which its
magnetic circuit is most nearly closed, it delivers its maximum induced
current, the phases of which so correspond with those of the primary
current that the motor will run as though both field and armature were
excited by the main current.
[Illustration: FIG. 36.]
To vary the speed of the motor to any rate between the minimum and
maximum rates, the core E and coils F are turned in either direction to
an extent which produces the desired result, for in its normal position
the convolutions of coil F embrace the maximum number of lines of force,
all of which act with the same effect upon the coil; hence it will
deliver its maximum current; but by turning the coil F out of its
position of maximum effect the number of lines of force embraced by it
is diminished. The inductive effect is therefore impaired, and the
current delivered by coil F will continue to diminish in proportion to
the angle at which the coil F is turned until, after passing through an
angle of ninety degrees, the convolutions of the coil will be at right
angles to those of coils C C, and the inductive effect reduced to a
minimum.
Incidentally to certain constructions, other causes may influence the
variation in the strength of the induced currents. For example, in the
present case it will be observed that by the first movement of coil F a
certain portion of its convolutions are carried beyond the line of the
direct influence of the lines of force, and that the magnetic path or
circuit for the lines is impaired; hence the inductive effect would be
reduced. Next, that after moving through a certain angle, which is
obviously determined by the relative dimensions of the bobbin or coil F,
diagonally opposite portions of the coil will be simultaneously included
in the field, but in such positions that the lines which produce a
current-impulse in one portion of the coil in a certain direction will
produce in the diagonally opposite portion a corresponding impulse in
the opposite direction; hence portions of the current will neutralize
one another.
As before stated, the mechanical construction of the device may be
greatly varied; but the essential conditions of the principle will be
fulfilled in any apparatus in which the movement of the elements with
respect to one another effects the same results by varying the inductive
relations of the two elements in a manner similar to that described.
[Illustration: FIG. 37.]
It may also be stated that the core E is not indispensable to the
operation of the regulator; but its presence is obviously beneficial.
This regulator, however, has another valuable property in its capability
of reversing the motor, for if the coil F be turned through a
half-revolution, the position of its convolutions relatively to the two
coils C C and to the lines of force is reversed, and consequently the
phases of the current will be reversed. This will produce a rotation of
the motor in an opposite direction. This form of regulator is also
applied with great advantage to Mr. Tesla's system of utilizing
alternating currents, in which the magnetic poles of the field of a
motor are progressively shifted by means of the combined effects upon
the field of magnetizing coils included in independent circuits, through
which pass alternating currents in proper order and relations to each
other.
In Fig. 37, let P represent a Tesla generator having two independent
coils, P' and P'', on the armature, and T a diagram of a motor having
two independent energizing coils or sets of coils, R R'. One of the
circuits from the generator, as S' S', includes one set, R' R', of the
energizing coils of the motor, while the other circuit, as S S, includes
the primary coils of the regulator. The secondary coil of the regulator
includes the other coils, R R, of the motor.
While the secondary coil of the regulator is in its normal position, it
produces its maximum current, and the maximum rotary effect is imparted
to the motor; but this effect will be diminished in proportion to the
angle at which the coil F of the regulator is turned. The motor will
also be reversed by reversing the position of the coil with reference to
the coils C C, and thereby reversing the phases of the current produced
by the generator. This changes the direction of the movement of the
shifting poles which the armature follows.
One of the main advantages of this plan of regulation is its economy of
power. When the induced coil is generating its maximum current, the
maximum amount of energy in the primary coils is absorbed; but as the
induced coil is turned from its normal position the self-induction of
the primary-coils reduces the expenditure of energy and saves power.
It is obvious that in practice either coils C C or coil F may be used as
primary or secondary, and it is well understood that their relative
proportions may be varied to produce any desired difference or
similarity in the inducing and induced currents.
CHAPTER VIII.
SINGLE CIRCUIT, SELF-STARTING SYNCHRONIZING MOTORS.
In the first chapters of this section we have, bearing in mind the broad
underlying principle, considered a distinct class of motors, namely,
such as require for their operation a special generator capable of
yielding currents of differing phase. As a matter of course, Mr. Tesla
recognizing the desirability of utilizing his motors in connection with
ordinary systems of distribution, addressed himself to the task of
inventing various methods and ways of achieving this object. In the
succeeding chapters, therefore, we witness the evolution of a number of
ideas bearing upon this important branch of work. It must be obvious to
a careful reader, from a number of hints encountered here and there,
that even the inventions described in these chapters to follow do not
represent the full scope of the work done in these lines. They might,
indeed, be regarded as exemplifications.
We will present these various inventions in the order which to us
appears the most helpful to an understanding of the subject by the
majority of readers. It will be naturally perceived that in offering a
series of ideas of this nature, wherein some of the steps or links are
missing, the descriptions are not altogether sequential; but any one who
follows carefully the main drift of the thoughts now brought together
will find that a satisfactory comprehension of the principles can be
gained.
As is well known, certain forms of alternating-current machines have the
property, when connected in circuit with an alternating current
generator, of running as a motor in synchronism therewith; but, while
the alternating current will run the motor after it has attained a rate
of speed synchronous with that of the generator, it will not start it.
Hence, in all instances heretofore where these "synchronizing motors,"
as they are termed, have been run, some means have been adopted to bring
the motors up to synchronism with the generator, or approximately so,
before the alternating current of the generator is applied to drive
them. In some instances mechanical appliances have been utilized for
this purpose. In others special and complicated forms of motor have been
constructed. Mr. Tesla has discovered a much more simple method or plan
of operating synchronizing motors, which requires practically no other
apparatus than the motor itself. In other words, by a certain change in
the circuit connections of the motor he converts it at will from a
double circuit motor, or such as have been already described, and which
will start under the action of an alternating current, into a
synchronizing motor, or one which will be run by the generator only when
it has reached a certain speed of rotation synchronous with that of the
generator. In this manner he is enabled to extend very greatly the
applications of his system and to secure all the advantages of both
forms of alternating current motor.
The expression "synchronous with that of the generator," is used here in
its ordinary acceptation--that is to say, a motor is said to synchronize
with the generator when it preserves a certain relative speed determined
by its number of poles and the number of alternations produced per
revolution of the generator. Its actual speed, therefore, may be faster
or slower than that of the generator; but it is said to be synchronous
so long as it preserves the same relative speed.
In carrying out this invention Mr. Tesla constructs a motor which has a
strong tendency to synchronism with the generator. The construction
preferred is that in which the armature is provided with polar
projections. The field-magnets are wound with two sets of coils, the
terminals of which are connected to a switch mechanism, by means of
which the line-current may be carried directly through these coils or
indirectly through paths by which its phases are modified. To start such
a motor, the switch is turned on to a set of contacts which includes in
one motor circuit a dead resistance, in the other an inductive
resistance, and, the two circuits being in derivation, it is obvious
that the difference in phase of the current in such circuits will set up
a rotation of the motor. When the speed of the motor has thus been
brought to the desired rate the switch is shifted to throw the main
current directly through the motor-circuits, and although the currents
in both circuits will now be of the same phase the motor will continue
to revolve, becoming a true synchronous motor. To secure greater
efficiency, the armature or its polar projections are wound with coils
closed on themselves.
In the accompanying diagrams, Fig. 38 illustrates the details of the
plan above set forth, and Figs. 39 and 40 modifications of the same.
[Illustration: FIGS. 38, 39 and 40.]
Referring to Fig. 38, let A designate the field-magnets of a motor, the
polar projections of which are wound with coils B C included in
independent circuits, and D the armature with polar projections wound
with coils E closed upon themselves, the motor in these respects being
similar in construction to those described already, but having on
account of the polar projections on the armature core, or other similar
and well-known features, the properties of a synchronizing-motor. L L'
represents the conductors of a line from an alternating current
generator G.
Near the motor is placed a switch the action of which is that of the one
shown in the diagrams, which is constructed as follows: F F' are two
conducting plates or arms, pivoted at their ends and connected by an
insulating cross-bar, H, so as to be shifted in parallelism. In the path
of the bars F F' is the contact 2, which forms one terminal of the
circuit through coils C, and the contact 4, which is one terminal of the
circuit through coils B. The opposite end of the wire of coils C is
connected to the wire L or bar F', and the corresponding end of coils B
is connected to wire L' and bar F; hence if the bars be shifted so as to
bear on contacts 2 and 4 both sets of coils B C will be included in the
circuit L L' in multiple arc or derivation. In the path of the levers F
F' are two other contact terminals, 1 and 3. The contact 1 is connected
to contact 2 through an artificial resistance, I, and contact 3 with
contact 4 through a self-induction coil, J, so that when the switch
levers are shifted upon the points 1 and 3 the circuits of coils B and C
will be connected in multiple arc or derivation to the circuit L L', and
will include the resistance and self-induction coil respectively. A
third position of the switch is that in which the levers F and F' are
shifted out of contact with both sets of points. In this case the motor
is entirely out of circuit.
The purpose and manner of operating the motor by these devices are as
follows: The normal position of the switch, the motor being out of
circuit, is off the contact points. Assuming the generator to be
running, and that it is desired to start the motor, the switch is
shifted until its levers rest upon points 1 and 3. The two
motor-circuits are thus connected with the generator circuit; but by
reason of the presence of the resistance I in one and the self-induction
coil J in the other the coincidence of the phases of the current is
disturbed sufficiently to produce a progression of the poles, which
starts the motor in rotation. When the speed of the motor has run up to
synchronism with the generator, or approximately so, the switch is
shifted over upon the points 2 and 4, thus cutting out the coils I and
J, so that the currents in both circuits have the same phase; but the
motor now runs as a synchronous motor.
It will be understood that when brought up to speed the motor will run
with only one of the circuits B or C connected with the main or
generator circuit, or the two circuits may be connected in series. This
latter plan is preferable when a current having a high number of
alternations per unit of time is employed to drive the motor. In such
case the starting of the motor is more difficult, and the dead and
inductive resistances must take up a considerable proportion of the
electromotive force of the circuits. Generally the conditions are so
adjusted that the electromotive force used in each of the motor circuits
is that which is required to operate the motor when its circuits are in
series. The plan followed in this case is illustrated in Fig. 39. In
this instance the motor has twelve poles and the armature has polar
projections D wound with closed coils E. The switch used is of
substantially the same construction as that shown in the previous
figure. There are, however, five contacts, designated as 5, 6, 7, 8, and
9. The motor-circuits B C, which include alternate field-coils, are
connected to the terminals in the following order: One end of circuit C
is connected to contact 9 and to contact 5 through a dead resistance, I.
One terminal of circuit B is connected to contact 7 and to contact 6
through a self-induction coil, J. The opposite terminals of both
circuits are connected to contact 8.
One of the levers, as F, of the switch is made with an extension, _f_,
or otherwise, so as to cover both contacts 5 and 6 when shifted into the
position to start the motor. It will be observed that when in this
position and with lever F' on contact 8 the current divides between the
two circuits B C, which from their difference in electrical character
produce a progression of the poles that starts the motor in rotation.
When the motor has attained the proper speed, the switch is shifted so
that the levers cover the contacts 7 and 9, thereby connecting circuits
B and C in series. It is found that by this disposition the motor is
maintained in rotation in synchronism with the generator. This principle
of operation, which consists in converting by a change of connections or
otherwise a double-circuit motor, or one operating by a progressive
shifting of the poles, into an ordinary synchronizing motor may be
carried out in many other ways. For instance, instead of using the
switch shown in the previous figures, we may use a temporary ground
circuit between the generator and motor, in order to start the motor, in
substantially the manner indicated in Fig. 40. Let G in this figure
represent an ordinary alternating-current generator with, say, two
poles, M M', and an armature wound with two coils, N N', at right angles
and connected in series. The motor has, for example, four poles wound
with coils B C, which are connected in series, and an armature with
polar projections D wound with closed coils E E. From the common joint
or union between the two circuits of both the generator and the motor an
earth connection is established, while the terminals or ends of these
circuits are connected to the line. Assuming that the motor is a
synchronizing motor or one that has the capability of running in
synchronism with the generator, but not of starting, it may be started
by the above-described apparatus by closing the ground connection from
both generator and motor. The system thus becomes one with a two-circuit
generator and motor, the ground forming a common return for the currents
in the two circuits L and L'. When by this arrangement of circuits the
motor is brought to speed, the ground connection is broken between the
motor or generator, or both, ground-switches P P' being employed for
this purpose. The motor then runs as a synchronizing motor.
In describing the main features which constitute this invention
illustrations have necessarily been omitted of the appliances used in
conjunction with the electrical devices of similar systems--such, for
instance, as driving-belts, fixed and loose pulleys for the motor, and
the like; but these are matters well understood.
Mr. Tesla believes he is the first to operate electro-magnetic motors by
alternating currents in any of the ways herein described--that is to
say, by producing a progressive movement or rotation of their poles or
points of greatest magnetic attraction by the alternating currents until
they have reached a given speed, and then by the same currents producing
a simple alternation of their poles, or, in other words, by a change in
the order or character of the circuit connections to convert a motor
operating on one principle to one operating on another.
CHAPTER IX.
CHANGE FROM DOUBLE CURRENT TO SINGLE CURRENT MOTOR.
A description is given elsewhere of a method of operating alternating
current motors by first rotating their magnetic poles until they have
attained synchronous speed, and then alternating the poles. The motor is
thus transformed, by a simple change of circuit connections from one
operated by the action of two or more independent energizing currents to
one operated either by a single current or by several currents acting as
one. Another way of doing this will now be described.
At the start the magnetic poles of one element or field of the motor are
progressively shifted by alternating currents differing in phase and
passed through independent energizing circuits, and short circuit the
coils of the other element. When the motor thus started reaches or
passes the limit of speed synchronous with the generator, Mr. Tesla
connects up the coils previously short-circuited with a source of direct
current and by a change of the circuit connections produces a simple
alternation of the poles. The motor then continues to run in synchronism
with the generator. The motor here shown in Fig. 41 is one of the
ordinary forms, with field-cores either laminated or solid and with a
cylindrical laminated armature wound, for example, with the coils A B at
right angles. The shaft of the armature carries three collecting or
contact rings C D E. (Shown, for better illustration, as of different
diameters.)
One end of coil A connects to one ring, as C, and one end of coil B
connects with ring D. The remaining ends are connected to ring E.
Collecting springs or brushes F G H bear upon the rings and lead to the
contacts of a switch, to be presently described. The field-coils have
their terminals in binding-posts K K, and may be either closed upon
themselves or connected with a source of direct current L, by means of a
switch M. The main or controlling switch has five contacts _a b c d e_
and two levers _f g_, pivoted and connected by an insulating cross-bar
_h_, so as to move in parallelism. These levers are connected to the
line wires from a source of alternating currents N. Contact _a_ is
connected to brush G and coil B through a dead resistance R and wire P.
Contact _b_ is connected with brush F and coil A through a
self-induction coil S and wire O. Contacts _c_ and _e_ are connected to
brushes G F, respectively, through the wires P O, and contact _d_ is
directly connected with brush H. The lever _f_ has a widened end, which
may span the contacts _a b_. When in such position and with lever _g_ on
contact _d_, the alternating currents divide between the two
motor-coils, and by reason of their different self-induction a
difference of current-phase is obtained that starts the motor in
rotation. In starting, the field-coils are short circuited.
[Illustration: FIG. 41.]
When the motor has attained the desired speed, the switch is shifted to
the position shown in dotted lines--that is to say, with the levers _f
g_ resting on points _c e_. This connects up the two armature coils in
series, and the motor will then run as a synchronous motor. The
field-coils are thrown into circuit with the direct current source when
the main switch is shifted.
CHAPTER X.
MOTOR WITH "CURRENT LAG" ARTIFICIALLY SECURED.
One of the general ways followed by Mr. Tesla in developing his rotary
phase motors is to produce practically independent currents differing
primarily in phase and to pass these through the motor-circuits. Another
way is to produce a single alternating current, to divide it between the
motor-circuits, and to effect artificially a lag in one of these
circuits or branches, as by giving to the circuits different
self-inductive capacity, and in other ways. In the former case, in which
the necessary difference of phase is primarily effected in the
generation of currents, in some instances, the currents are passed
through the energizing coils of both elements of the motor--the field
and armature; but a further result or modification may be obtained by
doing this under the conditions hereinafter specified in the case of
motors in which the lag, as above stated, is artificially secured.
Figs. 42 to 47, inclusive, are diagrams of different ways in which the
invention is carried out; and Fig. 48, a side view of a form of motor
used by Mr. Tesla for this purpose.
[Illustration: FIGS. 42, 43 and 44.]
A B in Fig. 42 indicate the two energizing circuits of a motor, and C D
two circuits on the armature. Circuit or coil A is connected in series
with circuit or coil C, and the two circuits B D are similarly
connected. Between coils A and C is a contact-ring _e_, forming one
terminal of the latter, and a brush _a_, forming one terminal of the
former. A ring _d_ and brush _c_ similarly connect coils B and D. The
opposite terminals of the field-coils connect to one binding post _h_ of
the motor, and those of the armature coils are similarly connected to
the opposite binding post _i_ through a contact-ring _f_ and brush _g_.
Thus each motor-circuit while in derivation to the other includes one
armature and one field coil. These circuits are of different
self-induction, and may be made so in various ways. For the sake
of clearness, an artificial resistance R is shown in one of these
circuits, and in the other a self-induction coil S. When an alternating
current is passed through this motor it divides between its two
energizing-circuits. The higher self-induction of one circuit produces a
greater retardation or lag in the current therein than in the other. The
difference of phase between the two currents effects the rotation or
shifting of the points of maximum magnetic effect that secures the
rotation of the armature. In certain respects this plan of including
both armature and field coils in circuit is a marked improvement. Such a
motor has a good torque at starting; yet it has also considerable
tendency to synchronism, owing to the fact that when properly
constructed the maximum magnetic effects in both armature and field
coincide--a condition which in the usual construction of these motors
with closed armature coils is not readily attained. The motor thus
constructed exhibits too, a better regulation of current from no load to
load, and there is less difference between the apparent and real energy
expended in running it. The true synchronous speed of this form of motor
is that of the generator when both are alike--that is to say, if the
number of the coils on the armature and on the field is _x_, the motor
will run normally at the same speed as a generator driving it if the
number of field magnets or poles of the same be also _x_.
[Illustration: FIGS. 45, 46 and 47.]
Fig. 43 shows a somewhat modified arrangement of circuits. There is in
this case but one armature coil E, the winding of which maintains
effects corresponding to the resultant poles produced by the two
field-circuits.
Fig. 44 represents a disposition in which both armature and field are
wound with two sets of coils, all in multiple arc to the line or main
circuit. The armature coils are wound to correspond with the field-coils
with respect to their self-induction. A modification of this plan is
shown in Fig. 45--that is to say, the two field coils and two armature
coils are in derivation to themselves and in series with one another.
The armature coils in this case, as in the previous figure, are wound
for different self-induction to correspond with the field coils.
Another modification is shown in Fig. 46. In this case only one
armature-coil, as D, is included in the line-circuit, while the other,
as C, is short-circuited.
In such a disposition as that shown in Fig. 43, or where only one
armature-coil is employed, the torque on the start is somewhat reduced,
while the tendency to synchronism is somewhat increased. In such a
disposition as shown in Fig. 46, the opposite conditions would exist. In
both instances, however, there is the advantage of dispensing with one
contact-ring.
[Illustration: FIG. 48.]
In Fig. 46 the two field-coils and the armature-coil D are in multiple
arc. In Fig. 47 this disposition is modified, coil D being shown in
series with the two field-coils.
Fig. 48 is an outline of the general form of motor in which this
invention is embodied. The circuit connections between the armature and
field coils are made, as indicated in the previous figures, through
brushes and rings, which are not shown.
CHAPTER XI.
ANOTHER METHOD OF TRANSFORMATION FROM A TORQUE TO A SYNCHRONIZING MOTOR.
In a preceding chapter we have described a method by which Mr. Tesla
accomplishes the change in his type of rotating field motor from a
torque to a synchronizing motor. As will be observed, the desired end is
there reached by a change in the circuit connections at the proper
moment. We will now proceed to describe another way of bringing about
the same result. The principle involved in this method is as follows:--
If an alternating current be passed through the field coils only of a
motor having two energizing circuits of different self-induction and the
armature coils be short-circuited, the motor will have a strong torque,
but little or no tendency to synchronism with the generator; but if the
same current which energizes the field be passed also through the
armature coils the tendency to remain in synchronism is very
considerably increased. This is due to the fact that the maximum
magnetic effects produced in the field and armature more nearly
coincide. On this principle Mr. Tesla constructs a motor having
independent field circuits of different self-induction, which are joined
in derivation to a source of alternating currents. The armature is wound
with one or more coils, which are connected with the field coils through
contact rings and brushes, and around the armature coils a shunt is
arranged with means for opening or closing the same. In starting this
motor the shunt is closed around the armature coils, which will
therefore be in closed circuit. When the current is directed through the
motor, it divides between the two circuits, (it is not necessary to
consider any case where there are more than two circuits used), which,
by reason of their different self-induction, secure a difference of
phase between the two currents in the two branches, that produces a
shifting or rotation of the poles. By the alternations of current, other
currents are induced in the closed--or short-circuited--armature coils
and the motor has a strong torque. When the desired speed is reached,
the shunt around the armature-coils is opened and the current directed
through both armature and field coils. Under these conditions the motor
has a strong tendency to synchronism.
[Illustration: FIGS. 49, 50 and 51.]
In Fig. 49, A and B designate the field coils of the motor. As the
circuits including these coils are of different self-induction, this is
represented by a resistance coil R in circuit with A, and a
self-induction coil S in circuit with B. The same result may of course
be secured by the winding of the coils. C is the armature circuit, the
terminals of which are rings _a b_. Brushes _c d_ bear on these rings
and connect with the line and field circuits. D is the shunt or short
circuit around the armature. E is the switch in the shunt.
It will be observed that in such a disposition as is illustrated in
Fig. 49, the field circuits A and B being of different self-induction,
there will always be a greater lag of the current in one than the other,
and that, generally, the armature phases will not correspond with
either, but with the resultant of both. It is therefore important to
observe the proper rule in winding the armature. For instance, if the
motor have eight poles--four in each circuit--there will be four
resultant poles, and hence the armature winding should be such as to
produce four poles, in order to constitute a true synchronizing motor.
[Illustration: FIG. 52.]
The diagram, Fig. 50, differs from the previous one only in respect to
the order of connections. In the present case the armature-coil, instead
of being in series with the field-coils, is in multiple arc therewith.
The armature-winding may be similar to that of the field--that is to
say, the armature may have two or more coils wound or adapted for
different self-induction and adapted, preferably, to produce the same
difference of phase as the field-coils. On starting the motor the shunt
is closed around both coils. This is shown in Fig. 51, in which the
armature coils are F G. To indicate their different electrical
character, there are shown in circuit with them, respectively, the
resistance R' and the self-induction coil S'. The two armature coils are
in series with the field-coils and the same disposition of the shunt or
short-circuit D is used. It is of advantage in the operation of motors
of this kind to construct or wind the armature in such manner that when
short-circuited on the start it will have a tendency to reach a higher
speed than that which synchronizes with the generator. For example, a
given motor having, say, eight poles should run, with the armature coil
short-circuited, at two thousand revolutions per minute to bring it up
to synchronism. It will generally happen, however, that this speed is
not reached, owing to the fact that the armature and field currents do
not properly correspond, so that when the current is passed through the
armature (the motor not being quite up to synchronism) there is a
liability that it will not "hold on," as it is termed. It is preferable,
therefore, to so wind or construct the motor that on the start, when the
armature coils are short-circuited, the motor will tend to reach a speed
higher than the synchronous--as for instance, double the latter. In such
case the difficulty above alluded to is not felt, for the motor will
always hold up to synchronism if the synchronous speed--in the case
supposed of two thousand revolutions--is reached or passed. This may be
accomplished in various ways; but for all practical purposes the
following will suffice: On the armature are wound two sets of coils. At
the start only one of these is short-circuited, thereby producing a
number of poles on the armature, which will tend to run the speed up
above the synchronous limit. When such limit is reached or passed, the
current is directed through the other coil, which, by increasing the
number of armature poles, tends to maintain synchronism.
[Illustration: FIG. 53.]
In Fig. 52, such a disposition is shown. The motor having, say, eight
poles contains two field-circuits A and B, of different self-induction.
The armature has two coils F and G. The former is closed upon itself,
the latter connected with the field and line through contact-rings _a
b_, brushes _c d_, and a switch E. On the start the coil F alone is
active and the motor tends to run at a speed above the synchronous; but
when the coil G is connected to the circuit the number of armature poles
is increased, while the motor is made a true synchronous motor. This
disposition has the advantage that the closed armature-circuit imparts
to the motor torque when the speed falls off, but at the same time the
conditions are such that the motor comes out of synchronism more
readily. To increase the tendency to synchronism, two circuits may be
used on the armature, one of which is short-circuited on the start and
both connected with the external circuit after the synchronous speed is
reached or passed. This disposition is shown in Fig. 53. There are three
contact-rings _a b e_ and three brushes _c d f_, which connect the
armature circuits with the external circuit. On starting, the switch H
is turned to complete the connection between one binding-post P and the
field-coils. This short-circuits one of the armature-coils, as G. The
other coil F is out of circuit and open. When the motor is up to speed,
the switch H is turned back, so that the connection from binding-post P
to the field coils is through the coil G, and switch K is closed,
thereby including coil F in multiple arc with the field coils. Both
armature coils are thus active.
From the above-described instances it is evident that many other
dispositions for carrying out the invention are possible.
CHAPTER XII.
"MAGNETIC LAG" MOTOR.
The following description deals with another form of motor, namely,
depending on "magnetic lag" or hysteresis, its peculiarity being that in
it the attractive effects or phases while lagging behind the phases of
current which produce them, are manifested simultaneously and not
successively. The phenomenon utilized thus at an early stage by Mr.
Tesla, was not generally believed in by scientific men, and Prof. Ayrton
was probably first to advocate it or to elucidate the reason of its
supposed existence.
Fig. 54 is a side view of the motor, in elevation. Fig. 55 is a
part-sectional view at right angles to Fig. 54. Fig. 56 is an end view
in elevation and part section of a modification, and Fig. 57 is a
similar view of another modification.
In Figs. 54 and 55, A designates a base or stand, and B B the
supporting-frame of the motor. Bolted to the supporting-frame are two
magnetic cores or pole-pieces C C', of iron or soft steel. These may be
subdivided or laminated, in which case hard iron or steel plates or bars
should be used, or they should be wound with closed coils. D is a
circular disc armature, built up of sections or plates of iron and
mounted in the frame between the pole-pieces C C', curved to conform to
the circular shape thereof. This disc may be wound with a number of
closed coils E. F F are the main energizing coils, supported by the
supporting-frame, so as to include within their magnetizing influence
both the pole-pieces C C' and the armature D. The pole-pieces C C'
project out beyond the coils F F on opposite sides, as indicated in the
drawings. If an alternating current be passed through the coils F F,
rotation of the armature will be produced, and this rotation is
explained by the following apparent action, or mode of operation: An
impulse of current in the coils F F establishes two polarities in the
motor. The protruding end of pole-piece C, for instance, will be of one
sign, and the corresponding end of pole-piece C' will be of the opposite
sign. The armature also exhibits two poles at right angles to the coils
F F, like poles to those in the pole-pieces being on the same side of
the coils. While the current is flowing there is no appreciable tendency
to rotation developed; but after each current impulse ceases or begins
to fall, the magnetism in the armature and in the ends of the
pole-pieces C C' lags or continues to manifest itself, which produces a
rotation of the armature by the repellent force between the more closely
approximating points of maximum magnetic effect. This effect is
continued by the reversal of current, the polarities of field and
armature being simply reversed. One or both of the elements--the
armature or field--may be wound with closed induced coils to intensify
this effect. Although in the illustrations but one of the fields is
shown, each element of the motor really constitutes a field, wound with
the closed coils, the currents being induced mainly in those
convolutions or coils which are parallel to the coils F F.
[Illustration: FIG. 54.]
[Illustration: FIG. 55.]
A modified form of this motor is shown in Fig. 56. In this form G is one
of two standards that support the bearings for the armature-shaft. H H
are uprights or sides of a frame, preferably magnetic, the ends C C' of
which are bent in the manner indicated, to conform to the shape of the
armature D and form field-magnet poles. The construction of the armature
may be the same as in the previous figure, or it may be simply a
magnetic disc or cylinder, as shown, and a coil or coils F F are
secured in position to surround both the armature and the poles C C'.
The armature is detachable from its shaft, the latter being passed
through the armature after it has been inserted in position. The
operation of this form of motor is the same in principle as that
previously described and needs no further explanation.
[Illustration: FIG. 56.]
[Illustration: FIG. 57.]
One of the most important features in alternating current motors is,
however, that they should be adapted to and capable of running
efficiently on the alternating circuits in present use, in which almost
without exception the generators yield a very high number of
alternations. Such a motor, of the type under consideration, Mr. Tesla
has designed by a development of the principle of the motor shown in
Fig. 56, making a multipolar motor, which is illustrated in Fig. 57. In
the construction of this motor he employs an annular magnetic frame J,
with inwardly-extending ribs or projections K, the ends of which all
bend or turn in one direction and are generally shaped to conform to the
curved surface of the armature. Coils F F are wound from one part K to
the one next adjacent, the ends or loops of each coil or group of wires
being carried over toward the shaft, so as to form U-shaped groups
of convolutions at each end of the armature. The pole-pieces C C', being
substantially concentric with the armature, form ledges, along which the
coils are laid and should project to some extent beyond the the coils,
as shown. The cylindrical or drum armature D is of the same construction
as in the other motors described, and is mounted to rotate within the
annular frame J and between the U-shaped ends or bends of the
coils F. The coils F are connected in multiple or in series with a
source of alternating currents, and are so wound that with a current or
current impulse of given direction they will make the alternate
pole-pieces C of one polarity and the other pole-pieces C' of the
opposite polarity. The principle of the operation of this motor is the
same as the other above described, for, considering any two pole-pieces
C C', a current impulse passing in the coil which bridges them or is
wound over both tends to establish polarities in their ends of opposite
sign and to set up in the armature core between them a polarity of the
same sign as that of the nearest pole-piece C. Upon the fall or
cessation of the current impulse that established these polarities the
magnetism which lags behind the current phase, and which continues to
manifest itself in the polar projections C C' and the armature, produces
by repulsion a rotation of the armature. The effect is continued by each
reversal of the current. What occurs in the case of one pair of
pole-pieces occurs simultaneously in all, so that the tendency to
rotation of the armature is measured by the sum of all the forces
exerted by the pole-pieces, as above described. In this motor also the
magnetic lag or effect is intensified by winding one or both cores with
closed induced coils. The armature core is shown as thus wound. When
closed coils are used, the cores should be laminated.
It is evident that a pulsatory as well as an alternating current might
be used to drive or operate the motors above described.
It will be understood that the degree of subdivision, the mass of the
iron in the cores, their size and the number of alternations in the
current employed to run the motor, must be taken into consideration in
order to properly construct this motor. In other words, in all such
motors the proper relations between the number of alternations and the
mass, size, or quality of the iron must be preserved in order to secure
the best results.
CHAPTER XIII.
METHOD OF OBTAINING DIFFERENCE OF PHASE BY MAGNETIC SHIELDING.
In that class of motors in which two or more sets of energizing magnets
are employed, and in which by artificial means a certain interval of
time is made to elapse between the respective maximum or minimum periods
or phases of their magnetic attraction or effect, the interval or
difference in phase between the two sets of magnets is limited in
extent. It is desirable, however, for the economical working of such
motors that the strength or attraction of one set of magnets should be
maximum, at the time when that of the other set is minimum, and
conversely; but these conditions have not heretofore been realized
except in cases where the two currents have been obtained from
independent sources in the same or different machines. Mr. Tesla has
therefore devised a motor embodying conditions that approach more nearly
the theoretical requirements of perfect working, or in other words, he
produces artificially a difference of magnetic phase by means of a
current from a single primary source sufficient in extent to meet the
requirements of practical and economical working. He employs a motor
with two sets of energizing or field magnets, each wound with coils
connected with a source of alternating or rapidly-varying currents, but
forming two separate paths or circuits. The magnets of one set are
protected to a certain extent from the energizing action of the current
by means of a magnetic shield or screen interposed between the magnet
and its energizing coil. This shield is properly adapted to the
conditions of particular cases, so as to shield or protect the main core
from magnetization until it has become itself saturated and no longer
capable of containing all the lines of force produced by the current. It
will be seen that by this means the energizing action begins in the
protected set of magnets a certain arbitrarily-determined period of time
later than in the other, and that by this means alone or in conjunction
with other means or devices heretofore employed a practical difference
of magnetic phase may readily be secured.
Fig. 58 is a view of a motor, partly in section, with a diagram
illustrating the invention. Fig. 59 is a similar view of a modification
of the same.
[Illustration: FIG. 58.]
[Illustration: FIG. 59.]
In Fig. 58, which exhibits the simplest form of the invention, A A is
the field-magnet of a motor, having, say, eight poles or
inwardly-projecting cores B and C. The cores B form one set of magnets
and are energized by coils D. The cores C, forming the other set are
energized by coils E, and the coils are connected, preferably, in series
with one another, in two derived or branched circuits, F G,
respectively, from a suitable source of current. Each coil E is
surrounded by a magnetic shield H, which is preferably composed of an
annealed, insulated, or oxidized iron wire wrapped or wound on the coils
in the manner indicated so as to form a closed magnetic circuit around
the coils and between the same and the magnetic cores C. Between the
pole pieces or cores B C is mounted the armature K, which, as is usual
in this type of machines, is wound with coils L closed upon themselves.
The operation resulting from this disposition is as follows: If a
current impulse be directed through the two circuits of the motor, it
will quickly energize the cores B, but not so the cores C, for the
reason that in passing through the coils E there is encountered the
influence of the closed magnetic circuits formed by the shields H. The
first effect is to retard effectively the current impulse in circuit G,
while at the same time the proportion of current which does pass does
not magnetize the cores C, which are shielded or screened by the
shields H. As the increasing electromotive force then urges more current
through the coils E, the iron wire H becomes magnetically saturated and
incapable of carrying all the lines of force, and hence ceases to
protect the cores C, which becomes magnetized, developing their maximum
effect after an interval of time subsequent to the similar manifestation
of strength in the other set of magnets, the extent of which is
arbitrarily determined by the thickness of the shield H, and other
well-understood conditions.
From the above it will be seen that the apparatus or device acts in two
ways. First, by retarding the current, and, second, by retarding the
magnetization of one set of the cores, from which its effectiveness will
readily appear.
Many modifications of the principle of this invention are possible. One
useful and efficient application of the invention is shown in Fig. 59.
In this figure a motor is shown similar in all respects to that above
described, except that the iron wire H, which is wrapped around the
coils E, is in this case connected in series with the coils D. The
iron-wire coils H, are connected and wound, so as to have little or no
self-induction, and being added to the resistance of the circuit F, the
action of the current in that circuit will be accelerated, while in the
other circuit G it will be retarded. The shield H may be made in many
forms, as will be understood, and used in different ways, as appears
from the foregoing description.
As a modification of his type of motor with "shielded" fields, Mr. Tesla
has constructed a motor with a field-magnet having two sets of poles or
inwardly-projecting cores and placed side by side, so as practically to
form two fields of force and alternately disposed--that is to say, with
the poles of one set or field opposite the spaces between the other. He
then connects the free ends of one set of poles by means of laminated
iron bands or bridge-pieces of considerably smaller cross-section than
the cores themselves, whereby the cores will all form parts of complete
magnetic circuits. When the coils on each set of magnets are connected
in multiple circuits or branches from a source of alternating currents,
electromotive forces are set up in or impressed upon each circuit
simultaneously; but the coils on the magnetically bridged or shunted
cores will have, by reason of the closed magnetic circuits, a high
self-induction, which retards the current, permitting at the beginning
of each impulse but little current to pass. On the other hand, no such
opposition being encountered in the other set of coils, the current
passes freely through them, magnetizing the poles on which they are
wound. As soon, however, as the laminated bridges become saturated and
incapable of carrying all the lines of force which the rising
electromotive force, and consequently increased current, produce, free
poles are developed at the ends of the cores, which, acting in
conjunction with the others, produce rotation of the armature.
The construction in detail by which this invention is illustrated is
shown in the accompanying drawings.
[Illustration: FIG. 60.]
[Illustration: FIG. 61.]
Fig. 60 is a view in side elevation of a motor embodying the principle.
Fig. 61 is a vertical cross-section of the motor. A is the frame of the
motor, which should be built up of sheets of iron punched out to the
desired shape and bolted together with insulation between the sheets.
When complete, the frame makes a field-magnet with inwardly projecting
pole-pieces B and C. To adapt them to the requirements of this
particular case these pole-pieces are out of line with one another,
those marked B surrounding one end of the armature and the others, as C,
the opposite end, and they are disposed alternately--that is to say, the
pole-pieces of one set occur in line with the spaces between those of
the other sets.
The armature D is of cylindrical form, and is also laminated in the
usual way and is wound longitudinally with coils closed upon themselves.
The pole-pieces C are connected or shunted by bridge-pieces E. These may
be made independently and attached to the pole-pieces, or they may be
parts of the forms or blanks stamped or punched out of sheet-iron. Their
size or mass is determined by various conditions, such as the strength
of the current to be employed, the mass or size of the cores to which
they are applied, and other familiar conditions.
Coils F surround the pole-pieces B, and other coils G are wound on the
pole-pieces C. These coils are connected in series in two circuits,
which are branches of a circuit from a generator of alternating
currents, and they may be so wound, or the respective circuits in which
they are included may be so arranged, that the circuit of coils G will
have, independently of the particular construction described, a higher
self-induction than the other circuit or branch.
The function of the shunts or bridges E is that they shall form with the
cores C a closed magnetic circuit for a current up to a predetermined
strength, so that when saturated by such current and unable to carry
more lines of force than such a current produces they will to no further
appreciable extent interfere with the development, by a stronger
current, of free magnetic poles at the ends of the cores C.
In such a motor the current is so retarded in the coils G, and the
manifestation of the free magnetism in the poles C is so delayed beyond
the period of maximum magnetic effect in poles B, that a strong torque
is produced and the motor operates with approximately the power
developed in a motor of this kind energized by independently generated
currents differing by a full quarter phase.
CHAPTER XIV.
TYPE OF TESLA SINGLE-PHASE MOTOR.
Up to this point, two principal types of Tesla motors have been
described: First, those containing two or more energizing circuits
through which are caused to pass alternating currents differing from one
another in phase to an extent sufficient to produce a continuous
progression or shifting of the poles or points of greatest magnetic
effect, in obedience to which the movable element of the motor is
maintained in rotation; second, those containing poles, or parts of
different magnetic susceptibility, which under the energizing influence
of the same current or two currents coinciding in phase will exhibit
differences in their magnetic periods or phases. In the first class of
motors the torque is due to the magnetism established in different
portions of the motor by currents from the same or from independent
sources, and exhibiting time differences in phase. In the second class
the torque results from the energizing effects of a current upon
different parts of the motor which differ in magnetic susceptibility--in
other words, parts which respond in the same relative degree to the
action of a current, not simultaneously, but after different intervals
of time.
In another Tesla motor, however, the torque, instead of being solely the
result of a time difference in the magnetic periods or phases of the
poles or attractive parts to whatever cause due, is produced by an
angular displacement of the parts which, though movable with respect to
one another, are magnetized simultaneously, or approximately so, by the
same currents. This principle of operation has been embodied practically
in a motor in which the necessary angular displacement between the
points of greatest magnetic attraction in the two elements of the
motor--the armature and field--is obtained by the direction of the
lamination of the magnetic cores of the elements.
Fig. 62 is a side view of such a motor with a portion of its armature
core exposed. Fig. 63 is an end or edge view of the same. Fig. 64 is a
central cross-section of the same, the armature being shown mainly in
elevation.
[Illustration: FIG. 62.]
[Illustration: FIG. 63.]
[Illustration: FIG. 64.]
Let A A designate two plates built up of thin sections or laminae of soft
iron insulated more or less from one another and held together by bolts
_a_ and secured to a base B. The inner faces of these plates contain
recesses or grooves in which a coil or coils D are secured obliquely to
the direction of the laminations. Within the coils D is a disc E,
preferably composed of a spirally-wound iron wire or ribbon or a series
of concentric rings and mounted on a shaft F, having bearings in the
plates A A. Such a device when acted upon by an alternating current is
capable of rotation and constitutes a motor, the operation of which may
be explained in the following manner: A current or current-impulse
traversing the coils D tends to magnetize the cores A A and E, all of
which are within the influence of the field of the coils. The poles thus
established would naturally lie in the same line at right angles to the
coils D, but in the plates A they are deflected by reason of the
direction of the laminations, and appear at or near the extremities of
these plates. In the disc, however, where these conditions are not
present, the poles or points of greatest attraction are on a line at
right angles to the plane of the coils; hence there will be a torque
established by this angular displacement of the poles or magnetic lines,
which starts the disc in rotation, the magnetic lines of the armature
and field tending toward a position of parallelism. This rotation is
continued and maintained by the reversals of the current in coils D D,
which change alternately the polarity of the field-cores A A. This
rotary tendency or effect will be greatly increased by winding the disc
with conductors G, closed upon themselves and having a radial direction,
whereby the magnetic intensity of the poles of the disc will be greatly
increased by the energizing effect of the currents induced in the coils
G by the alternating currents in coils D.
The cores of the disc and field may or may not be of different magnetic
susceptibility--that is to say, they may both be of the same kind of
iron, so as to be magnetized at approximately the same instant by the
coils D; or one may be of soft iron and the other of hard, in order that
a certain time may elapse between the periods of their magnetization. In
either case rotation will be produced; but unless the disc is provided
with the closed energizing coils it is desirable that the
above-described difference of magnetic susceptibility be utilized to
assist in its rotation.
The cores of the field and armature may be made in various ways, as will
be well understood, it being only requisite that the laminations in each
be in such direction as to secure the necessary angular displacement of
the points of greatest attraction. Moreover, since the disc may be
considered as made up of an infinite number of radial arms, it is
obvious that what is true of a disc holds for many other forms of
armature.
CHAPTER XV.
MOTORS WITH CIRCUITS OF DIFFERENT RESISTANCE.
As has been pointed out elsewhere, the lag or retardation of the phases
of an alternating current is directly proportional to the self-induction
and inversely proportional to the resistance of the circuit through
which the current flows. Hence, in order to secure the proper
differences of phase between the two motor-circuits, it is desirable to
make the self-induction in one much higher and the resistance much lower
than the self-induction and resistance, respectively, in the other. At
the same time the magnetic quantities of the two poles or sets of poles
which the two circuits produce should be approximately equal. These
requirements have led Mr. Tesla to the invention of a motor having the
following general characteristics: The coils which are included in that
energizing circuit which is to have the higher self-induction are made
of coarse wire, or a conductor of relatively low resistance, and with
the greatest possible length or number of turns. In the other set of
coils a comparatively few turns of finer wire are used, or a wire of
higher resistance. Furthermore, in order to approximate the magnetic
quantities of the poles excited by these coils, Mr. Tesla employs in the
self-induction circuit cores much longer than those in the other or
resistance circuit.
Fig. 65 is a part sectional view of the motor at right angles to the
shaft. Fig. 66 is a diagram of the field circuits.
In Fig. 66, let A represent the coils in one motor circuit, and B those
in the other. The circuit A is to have the higher self-induction. There
are, therefore, used a long length or a large number of turns of coarse
wire in forming the coils of this circuit. For the circuit B, a smaller
conductor is employed, or a conductor of a higher resistance than
copper, such as German silver or iron, and the coils are wound with
fewer turns. In applying these coils to a motor, Mr. Tesla builds up a
field-magnet of plates C, of iron and steel, secured together in the
usual manner by bolts D. Each plate is formed with four (more or less)
long cores E, around which is a space to receive the coil and an equal
number of short projections F to receive the coils of the
resistance-circuit. The plates are generally annular in shape, having an
open space in the centre for receiving the armature G, which Mr. Tesla
prefers to wind with closed coils. An alternating current divided
between the two circuits is retarded as to its phases in the circuit A
to a much greater extent than in the circuit B. By reason of the
relative sizes and disposition of the cores and coils the magnetic
effect of the poles E and F upon the armature closely approximate.
[Illustration: FIG. 65.]
[Illustration: FIG. 66.]
An important result secured by the construction shown here is that these
coils which are designed to have the higher self-induction are almost
completely surrounded by iron, and that the retardation is thus very
materially increased.
CHAPTER XVI.
MOTOR WITH EQUAL MAGNETIC ENERGIES IN FIELD AND ARMATURE.
Let it be assumed that the energy as represented in the magnetism in the
field of a given rotating field motor is ninety and that of the armature
ten. The sum of these quantities, which represents the total energy
expended in driving the motor, is one hundred; but, assuming that the
motor be so constructed that the energy in the field is represented by
fifty, and that in the armature by fifty, the sum is still one hundred;
but while in the first instance the product is nine hundred, in the
second it is two thousand five hundred, and as the energy developed is
in proportion to these products it is clear that those motors are the
most efficient--other things being equal--in which the magnetic energies
developed in the armature and field are equal. These results Mr. Tesla
obtains by using the same amount of copper or ampere turns in both
elements when the cores of both are equal, or approximately so, and the
same current energizes both; or in cases where the currents in one
element are induced to those of the other he uses in the induced coils
an excess of copper over that in the primary element or conductor.
[Illustration: FIG. 67.]
The conventional figure of a motor here introduced, Fig. 67, will give
an idea of the solution furnished by Mr. Tesla for the specific problem.
Referring to the drawing, A is the field-magnet, B the armature, C the
field coils, and D the armature-coils of the motor.
Generally speaking, if the mass of the cores of armature and field be
equal, the amount of copper or ampere turns of the energizing coils on
both should also be equal; but these conditions will be modified in
different forms of machine. It will be understood that these results are
most advantageous when existing under the conditions presented where the
motor is running with its normal load, a point to be well borne in
mind.
CHAPTER XVII.
MOTORS WITH COINCIDING MAXIMA OF MAGNETIC EFFECT IN ARMATURE AND FIELD.
In this form of motor, Mr. Tesla's object is to design and build
machines wherein the maxima of the magnetic effects of the armature and
field will more nearly coincide than in some of the types previously
under consideration. These types are: First, motors having two or more
energizing circuits of the same electrical character, and in the
operation of which the currents used differ primarily in phase; second,
motors with a plurality of energizing circuits of different electrical
character, in or by means of which the difference of phase is produced
artificially, and, third, motors with a plurality of energizing
circuits, the currents in one being induced from currents in another.
Considering the structural and operative conditions of any one of
them--as, for example, that first named--the armature which is mounted
to rotate in obedience to the co-operative influence or action of the
energizing circuits has coils wound upon it which are closed upon
themselves and in which currents are induced by the energizing-currents
with the object and result of energizing the armature-core; but under
any such conditions as must exist in these motors, it is obvious that a
certain time must elapse between the manifestations of an energizing
current impulse in the field coils, and the corresponding magnetic state
or phase in the armature established by the current induced thereby;
consequently a given magnetic influence or effect in the field which is
the direct result of a primary current impulse will have become more or
less weakened or lost before the corresponding effect in the armature
indirectly produced has reached its maximum. This is a condition
unfavorable to efficient working in certain cases--as, for instance,
when the progress of the resultant poles or points of maximum attraction
is very great, or when a very high number of alternations is
employed--for it is apparent that a stronger tendency to rotation will
be maintained if the maximum magnetic attractions or conditions in both
armature and field coincide, the energy developed by a motor being
measured by the product of the magnetic quantities of the armature and
field.
To secure this coincidence of maximum magnetic effects, Mr. Tesla has
devised various means, as explained below. Fig. 68 is a diagrammatic
illustration of a Tesla motor system in which the alternating currents
proceed from independent sources and differ primarily in phase.
[Illustration: FIG. 68.]
[Illustration: FIG. 69.]
A designates the field-magnet or magnetic frame of the motor; B B,
oppositely located pole-pieces adapted to receive the coils of one
energizing circuit; and C C, similar pole-pieces for the coils of the
other energizing circuit. These circuits are designated, respectively,
by D E, the conductor D'' forming a common return to the generator G.
Between these poles is mounted an armature--for example, a ring or
annular armature, wound with a series of coils F, forming a closed
circuit or circuits. The action or operation of a motor thus constructed
is now well understood. It will be observed, however, that the magnetism
of poles B, for example, established by a current impulse in the coils
thereon, precedes the magnetic effect set up in the armature by the
induced current in coils F. Consequently the mutual attraction between
the armature and field-poles is considerably reduced. The same
conditions will be found to exist if, instead of assuming the poles B or
C as acting independently, we regard the ideal resultant of both acting
together, which is the real condition. To remedy this, the motor field
is constructed with secondary poles B' C', which are situated between
the others. These pole-pieces are wound with coils D' E', the former in
derivation to the coils D, the latter to coils E. The main or primary
coils D and E are wound for a different self-induction from that of the
coils D' and E', the relations being so fixed that if the currents in D
and E differ, for example, by a quarter-phase, the currents in each
secondary coil, as D' E', will differ from those in its appropriate
primary D or E by, say, forty-five degrees, or one-eighth of a period.
Now, assuming that an impulse or alternation in circuit or branch E is
just beginning, while in the branch D it is just falling from maximum,
the conditions are those of a quarter-phase difference. The ideal
resultant of the attractive forces of the two sets of poles B C
therefore may be considered as progressing from poles B to poles C,
while the impulse in E is rising to maximum, and that in D is falling to
zero or minimum. The polarity set up in the armature, however, lags
behind the manifestations of field magnetism, and hence the maximum
points of attraction in armature and field, instead of coinciding, are
angularly displaced. This effect is counteracted by the supplemental
poles B' C'. The magnetic phases of these poles succeed those of poles B
C by the same, or nearly the same, period of time as elapses between the
effect of the poles B C and the corresponding induced effect in the
armature; hence the magnetic conditions of poles B' C' and of the
armature more nearly coincide and a better result is obtained. As poles
B' C' act in conjunction with the poles in the armature established by
poles B C, so in turn poles C B act similarly with the poles set up by
B' C', respectively. Under such conditions the retardation of the
magnetic effect of the armature and that of the secondary poles will
bring the maximum of the two more nearly into coincidence and a
correspondingly stronger torque or magnetic attraction secured.
In such a disposition as is shown in Fig. 68 it will be observed that
as the adjacent pole-pieces of either circuit are of like polarity they
will have a certain weakening effect upon one another. Mr. Tesla
therefore prefers to remove the secondary poles from the direct
influence of the others. This may be done by constructing a motor with
two independent sets of fields, and with either one or two armatures
electrically connected, or by using two armatures and one field. These
modifications are illustrated further on.
[Illustration: FIG. 70.]
[Illustration: FIG. 71.]
Fig. 69 is a diagrammatic illustration of a motor and system in which
the difference of phase is artificially produced. There are two coils D
D in one branch and two coils E E in another branch of the main circuit
from the generator G. These two circuits or branches are of different
self-induction, one, as D, being higher than the other. This is
graphically indicated by making coils D much larger than coils E. By
reason of the difference in the electrical character of the two
circuits, the phases of current in one are retarded to a greater extent
than the other. Let this difference be thirty degrees. A motor thus
constructed will rotate under the action of an alternating current; but
as happens in the case previously described the corresponding magnetic
effects of the armature and field do not coincide owing to the time that
elapses between a given magnetic effect in the armature and the
condition of the field that produces it. The secondary or supplemental
poles B' C' are therefore availed of. There being thirty degrees
difference of phase between the currents in coils D E, the magnetic
effect of poles B' C' should correspond to that produced by a current
differing from the current in coils D or E by fifteen degrees. This we
can attain by winding each supplemental pole B' C' with two coils H H'.
The coils H are included in a derived circuit having the same
self-induction as circuit D, and coils H' in a circuit having the same
self-induction as circuit E, so that if these circuits differ by thirty
degrees the magnetism of poles B' C' will correspond to that produced by
a current differing from that in either D or E by fifteen degrees. This
is true in all other cases. For example, if in Fig. 68 the coils D' E'
be replaced by the coils H H' included in the derived circuits, the
magnetism of the poles B' C' will correspond in effect or phase, if it
may be so termed, to that produced by a current differing from that in
either circuit D or E by forty-five degrees, or one-eighth of a period.
This invention as applied to a derived circuit motor is illustrated in
Figs. 70 and 71. The former is an end view of the motor with the
armature in section and a diagram of connections, and Fig. 71 a vertical
section through the field. These figures are also drawn to show one of
the dispositions of two fields that may be adopted in carrying out the
principle. The poles B B C C are in one field, the remaining poles in
the other. The former are wound with primary coils I J and secondary
coils I' J', the latter with coils K L. The primary coils I J are in
derived circuits, between which, by reason of their different
self-induction, there is a difference of phase, say, of thirty degrees.
The coils I' K are in circuit with one another, as also are coils J' L,
and there should be a difference of phase between the currents in coils
K and L and their corresponding primaries of, say, fifteen degrees. If
the poles B C are at right angles, the armature-coils should be
connected directly across, or a single armature core wound from end to
end may be used; but if the poles B C be in line there should be an
angular displacement of the armature coils, as will be well understood.
The operation will be understood from the foregoing. The maximum
magnetic condition of a pair of poles, as B' B', coincides closely with
the maximum effect in the armature, which lags behind the corresponding
condition in poles B B.
CHAPTER XVIII.
MOTOR BASED ON THE DIFFERENCE OF PHASE IN THE MAGNETIZATION OF THE INNER
AND OUTER PARTS OF AN IRON CORE.
It is well known that if a magnetic core, even if laminated or
subdivided, be wound with an insulated coil and a current of electricity
be directed through the coil, the magnetization of the entire core does
not immediately ensue, the magnetizing effect not being exhibited in all
parts simultaneously. This may be attributed to the fact that the action
of the current is to energize first those laminae or parts of the core
nearest the surface and adjacent to the exciting-coil, and from thence
the action progresses toward the interior. A certain interval of time
therefore elapses between the manifestation of magnetism in the external
and the internal sections or layers of the core. If the core be thin or
of small mass, this effect may be inappreciable; but in the case of a
thick core, or even of a comparatively thin one, if the number of
alternations or rate of change of the current strength be very great,
the time interval occurring between the manifestations of magnetism in
the interior of the core and in those parts adjacent to the coil is more
marked. In the construction of such apparatus as motors which are
designed to be run by alternating or equivalent currents--such as
pulsating or undulating currents generally--Mr. Tesla found it desirable
and even necessary to give due consideration to this phenomenon and to
make special provisions in order to obviate its consequences. With the
specific object of taking advantage of this action or effect, and to
render it more pronounced, he constructs a field magnet in which the
parts of the core or cores that exhibit at different intervals of time
the magnetic effect imparted to them by alternating or equivalent
currents in an energizing coil or coils, are so placed with relation to
a rotating armature as to exert thereon their attractive effect
successively in the order of their magnetization. By this means he
secures a result similar to that which he had previously attained in
other forms or types of motor in which by means of one or more
alternating currents he has produced the rotation or progression of the
magnetic poles.
This new mode of operation will now be described. Fig. 72 is a side
elevation of such motor. Fig. 73 is a side elevation of a more
practicable and efficient embodiment of the invention. Fig. 74 is a
central vertical section of the same in the plane of the axis of
rotation.
[Illustration: FIGS. 72 and 73.]
Referring to Fig. 72, let X represent a large iron core, which may be
composed of a number of sheets or laminae of soft iron or steel.
Surrounding this core is a coil Y, which is connected with a source E of
rapidly varying currents. Let us consider now the magnetic conditions
existing in this core at any point, as _b_, at or near the centre, and
any other point, as _a_, nearer the surface. When a current impulse is
started in the magnetizing coil Y, the section or part at _a_, being
close to the coil, is immediately energized, while the section or part
at _b_, which, to use a convenient expression, is "protected" by the
intervening sections or layers between _a_ and _b_, does not at once
exhibit its magnetism. However, as the magnetization of _a_ increases,
_b_ becomes also affected, reaching finally its maximum strength some
time later than _a_. Upon the weakening of the current the magnetization
of _a_ first diminishes, while _b_ still exhibits its maximum strength;
but the continued weakening of _a_ is attended by a subsequent weakening
of _b_. Assuming the current to be an alternating one, _a_ will now be
reversed, while _b_ still continues of the first imparted polarity. This
action continues the magnetic condition of _b_, following that of _a_ in
the manner above described. If an armature--for instance, a simple disc
F, mounted to rotate freely on an axis--be brought into proximity to the
core, a movement of rotation will be imparted to the disc, the direction
depending upon its position relatively to the core, the tendency being
to turn the portion of the disc nearest to the core from _a_ to _b_, as
indicated in Fig. 72.
[Illustration: FIG. 74.]
This action or principle of operation has been embodied in a practicable
form of motor, which is illustrated in Fig. 73. Let A in that figure
represent a circular frame of iron, from diametrically opposite points
of the interior of which the cores project. Each core is composed of
three main parts B, B and C, and they are similarly formed with a
straight portion or body _e_, around which the energizing coil is wound,
a curved arm or extension _c_, and an inwardly projecting pole or end
_d_. Each core is made up of two parts B B, with their polar extensions
reaching in one direction, and a part C between the other two, and with
its polar extension reaching in the opposite direction. In order to
lessen in the cores the circulation of currents induced therein, the
several sections are insulated from one another in the manner usually
followed in such cases. These cores are wound with coils D, which are
connected in the same circuit, either in parallel or series, and
supplied with an alternating or a pulsating current, preferably the
former, by a generator E, represented diagrammatically. Between the
cores or their polar extensions is mounted a cylindrical or similar
armature F, wound with magnetizing coils G, closed upon themselves.
The operation of this motor is as follows: When a current impulse or
alternation is directed through the coils D, the sections B B of the
cores, being on the surface and in close proximity to the coils, are
immediately energized. The sections C, on the other hand, are protected
from the magnetizing influence of the coil by the interposed layers of
iron B B. As the magnetism of B B increases, however, the sections C are
also energized; but they do not attain their maximum strength until a
certain time subsequent to the exhibition by the sections B B of their
maximum. Upon the weakening of the current the magnetic strength of B B
first diminishes, while the sections C have still their maximum
strength; but as B B continue to weaken the interior sections are
similarly weakened. B B may then begin to exhibit an opposite polarity,
which is followed later by a similar change on C, and this action
continues. B B and C may therefore be considered as separate
field-magnets, being extended so as to act on the armature in the most
efficient positions, and the effect is similar to that in the other
forms of Tesla motor--viz., a rotation or progression of the maximum
points of the field of force. Any armature--such, for instance, as a
disc--mounted in this field would rotate from the pole first to exhibit
its magnetism to that which exhibits it later.
It is evident that the principle here described may be carried out in
conjunction with other means for securing a more favorable or efficient
action of the motor. For example, the polar extensions of the sections C
may be wound or surrounded by closed coils. The effect of these coils
will be to still more effectively retard the magnetization of the polar
extensions of C.
CHAPTER XIX.
ANOTHER TYPE OF TESLA INDUCTION MOTOR.
It will have been gathered by all who are interested in the advance of
the electrical arts, and who follow carefully, step by step, the work of
pioneers, that Mr. Tesla has been foremost to utilize inductive effects
in permanently closed circuits, in the operation of alternating motors.
In this chapter one simple type of such a motor is described and
illustrated, which will serve as an exemplification of the principle.
Let it be assumed that an ordinary alternating current generator is
connected up in a circuit of practically no self-induction, such, for
example, as a circuit containing incandescent lamps only. On the
operation of the machine, alternating currents will be developed in the
circuit, and the phases of these currents will theoretically coincide
with the phases of the impressed electromotive force. Such currents may
be regarded and designated as the "unretarded currents."
It will be understood, of course, that in practice there is always more
or less self-induction in the circuit, which modifies to a corresponding
extent these conditions; but for convenience this may be disregarded in
the consideration of the principle of operation, since the same laws
apply. Assume next that a path of currents be formed across any two
points of the above circuit, consisting, for example, of the primary of
an induction device. The phases of the currents passing through the
primary, owing to the self-induction of the same, will not coincide with
the phases of the impressed electromotive force, but will lag behind,
such lag being directly proportional to the self-induction and inversely
proportional to the resistance of the said coil. The insertion of this
coil will also cause a lagging or retardation of the currents traversing
and delivered by the generator behind the impressed electromotive force,
such lag being the mean or resultant of the lag of the current through
the primary alone and of the "unretarded current" in the entire working
circuit. Next consider the conditions imposed by the association in
inductive relation with the primary coil, of a secondary coil. The
current generated in the secondary coil will react upon the primary
current, modifying the retardation of the same, according to the amount
of self-induction and resistance in the secondary circuit. If the
secondary circuit has but little self-induction--as, for instance, when
it contains incandescent lamps only--it will increase the actual
difference of phase between its own and the primary current, first, by
diminishing the lag between the primary current and the impressed
electromotive force, and, second, by its own lag or retardation behind
the impressed electromotive force. On the other hand, if the secondary
circuit have a high self-induction, its lag behind the current in the
primary is directly increased, while it will be still further increased
if the primary have a very low self-induction. The better results are
obtained when the primary has a low self-induction.
[Illustration: FIG. 75.]
[Illustration: FIG. 76.]
Fig. 75 is a diagram of a Tesla motor embodying this principle. Fig. 76
is a similar diagram of a modification of the same. In Fig. 75 let A
designate the field-magnet of a motor which, as in all these motors, is
built up of sections or plates. B C are polar projections upon which the
coils are wound. Upon one pair of these poles, as C, are wound primary
coils D, which are directly connected to the circuit of an alternating
current generator G. On the same poles are also wound secondary coils F,
either side by side or over or under the primary coils, and these are
connected with other coils E, which surround the poles B B. The
currents in both primary and secondary coils in such a motor will be
retarded or will lag behind the impressed electromotive force; but to
secure a proper difference in phase between the primary and secondary
currents themselves, Mr. Tesla increases the resistance of the circuit
of the secondary and reduces as much as practicable its self-induction.
This is done by using for the secondary circuit, particularly in the
coils E, wire of comparatively small diameter and having but few turns
around the cores; or by using some conductor of higher specific
resistance, such as German silver; or by introducing at some point in
the secondary circuit an artificial resistance R. Thus the
self-induction of the secondary is kept down and its resistance
increased, with the result of decreasing the lag between the impressed
electro-motive force and the current in the primary coils and increasing
the difference of phase between the primary and secondary currents.
In the disposition shown in Fig. 76, the lag in the secondary is
increased by increasing the self-induction of that circuit, while the
increasing tendency of the primary to lag is counteracted by inserting
therein a dead resistance. The primary coils D in this case have a low
self-induction and high resistance, while the coils E F, included in the
secondary circuit, have a high self-induction and low resistance. This
may be done by the proper winding of the coils; or in the circuit
including the secondary coils E F, we may introduce a self-induction
coil S, while in the primary circuit from the generator G and including
coils D, there may be inserted a dead resistance R. By this means the
difference of phase between the primary and secondary is increased. It
is evident that both means of increasing the difference of
phase--namely, by the special winding as well as by the supplemental or
external inductive and dead resistance--may be employed conjointly.
In the operation of this motor the current impulses in the primary coils
induce currents in the secondary coils, and by the conjoint action of
the two the points of greatest magnetic attraction are shifted or
rotated.
In practice it is found desirable to wind the armature with closed coils
in which currents are induced by the action thereon of the primaries.
CHAPTER XX.
COMBINATIONS OF SYNCHRONIZING MOTOR AND TORQUE MOTOR.
In the preceding descriptions relative to synchronizing motors and
methods of operating them, reference has been made to the plan adopted
by Mr. Tesla, which consists broadly in winding or arranging the motor
in such manner that by means of suitable switches it could be started as
a multiple-circuit motor, or one operating by a progression of its
magnetic poles, and then, when up to speed, or nearly so, converted into
an ordinary synchronizing motor, or one in which the magnetic poles were
simply alternated. In some cases, as when a large motor is used and when
the number of alternations is very high, there is more or less
difficulty in bringing the motor to speed as a double or
multiple-circuit motor, for the plan of construction which renders the
motor best adapted to run as a synchronizing motor impairs its
efficiency as a torque or double-circuit motor under the assumed
conditions on the start. This will be readily understood, for in a large
synchronizing motor the length of the magnetic circuit of the polar
projections, and their mass, are so great that apparently considerable
time is required for magnetization and demagnetization. Hence with a
current of a very high number of alternations the motor may not respond
properly. To avoid this objection and to start up a synchronizing motor
in which these conditions obtain, Mr. Tesla has combined two motors, one
a synchronizing motor, the other a multiple-circuit or torque motor, and
by the latter he brings the first-named up to speed, and then either
throws the whole current into the synchronizing motor or operates
jointly both of the motors.
This invention involves several novel and useful features. It will be
observed, in the first place, that both motors are run, without
commutators of any kind, and, secondly, that the speed of the torque
motor may be higher than that of the synchronizing motor, as will be the
case when it contains a fewer number of poles or sets of poles, so that
the motor will be more readily and easily brought up to speed. Thirdly,
the synchronizing motor may be constructed so as to have a much more
pronounced tendency to synchronism without lessening the facility with
which it is started.
Fig. 77 is a part sectional view of the two motors; Fig. 78 an end view
of the synchronizing motor; Fig. 79 an end view and part section of the
torque or double-circuit motor; Fig. 80 a diagram of the circuit
connections employed; and Figs. 81, 82, 83, 84 and 85 are diagrams of
modified dispositions of the two motors.
[Illustration: FIG. 77.]
Inasmuch as neither motor is doing any work while the current is acting
upon the other, the two armatures are rigidly connected, both being
mounted upon the same shaft A, the field-magnets B of the synchronizing
and C of the torque motor being secured to the same base D. The
preferably larger synchronizing motor has polar projections on its
armature, which rotate in very close proximity to the poles of the
field, and in other respects it conforms to the conditions that are
necessary to secure synchronous action. The pole-pieces of the armature
are, however, wound with closed coils E, as this obviates the employment
of sliding contacts. The smaller or torque motor, on the other hand,
has, preferably, a cylindrical armature F, without polar projections and
wound with closed coils G. The field-coils of the torque motor are
connected up in two series H and I, and the alternating current from the
generator is directed through or divided between these two circuits in
any manner to produce a progression of the poles or points of maximum
magnetic effect. This result is secured by connecting the two
motor-circuits in derivation with the circuit from the generator,
inserting in one motor circuit a dead resistance and in the other a
self-induction coil, by which means a difference in phase between the
two divisions of the current is secured. If both motors have the same
number of field poles, the torque motor for a given number of
alternations will tend to run at double the speed of the other, for,
assuming the connections to be such as to give the best results, its
poles are divided into two series and the number of poles is virtually
reduced one-half, which being acted upon by the same number of
alternations tend to rotate the armature at twice the speed. By this
means the main armature is more easily brought to or above the required
speed. When the speed necessary for synchronism is imparted to the main
motor, the current is shifted from the torque motor into the other.
[Illustration: FIG. 78.]
[Illustration: FIG. 79.]
A convenient arrangement for carrying out this invention is shown in
Fig. 80, in which J J are the field coils of the synchronizing, and H I
the field coils of the torque motor. L L' are the conductors of the main
line. One end of, say, coils H is connected to wire L through a
self-induction coil M. One end of the other set of coils I is connected
to the same wire through a dead resistance N. The opposite ends of these
two circuits are connected to the contact _m_ of a switch, the handle or
lever of which is in connection with the line-wire L'. One end of the
field circuit of the synchronizing motor is connected to the wire L. The
other terminates in the switch-contact _n_. From the diagram it will be
readily seen that if the lever P be turned upon contact _m_, the torque
motor will start by reason of the difference of phase between the
currents in its two energizing circuits. Then when the desired speed is
attained, if the lever P be shifted upon contact _n_ the entire current
will pass through the field coils of the synchronizing motor and the
other will be doing no work.
The torque motor may be constructed and operated in various ways, many
of which have already been touched upon. It is not necessary that one
motor be cut out of circuit while the other is in, for both may be acted
upon by current at the same time, and Mr. Tesla has devised various
dispositions or arrangements of the two motors for accomplishing this.
Some of these arrangements are illustrated in Figs. 81 to 85.
[Illustration: FIG. 80.]
Referring to Fig. 81, let T designate the torque or multiple circuit
motor and S the synchronizing motor, L L' being the line-wires from a
source of alternating current. The two circuits of the torque motor of
different degrees of self-induction, and designated by N M, are
connected in derivation to the wire L. They are then joined and
connected to the energizing circuit of the synchronizing motor, the
opposite terminal of which is connected to wire L'. The two motors are
thus in series. To start them Mr. Tesla short-circuits the synchronizing
motor by a switch P', throwing the whole current through the torque
motor. Then when the desired speed is reached the switch P' is opened,
so that the current passes through both motors. In such an arrangement
as this it is obviously desirable for economical and other reasons that
a proper relation between the speeds of the two motors should be
observed.
In Fig. 82 another disposition is illustrated. S is the synchronizing
motor and T the torque motor, the circuits of both being in parallel. W
is a circuit also in derivation to the motor circuits and containing a
switch P''. S' is a switch in the synchronizing motor circuit. On the
start the switch S' is opened, cutting out the motor S. Then P'' is
opened, throwing the entire current through the motor T, giving it a
very strong torque. When the desired speed is reached, switch S' is
closed and the current divides between both motors. By means of switch
P'' both motors may be cut out.
[Illustration: FIGS. 81, 82, 83, 84 and 85.]
In Fig. 83 the arrangement is substantially the same, except that a
switch T' is placed in the circuit which includes the two circuits of
the torque motor. Fig. 84 shows the two motors in series, with a shunt
around both containing a switch S T. There is also a shunt around the
synchronizing motor S, with a switch P'. In Fig. 85 the same disposition
is shown; but each motor is provided with a shunt, in which are switches
P' and T'', as shown.
CHAPTER XXI.
MOTOR WITH A CONDENSER IN THE ARMATURE CIRCUIT.
We now come to a new class of motors in which resort is had to
condensers for the purpose of developing the required difference of
phase and neutralizing the effects of self-induction. Mr. Tesla early
began to apply the condenser to alternating apparatus, in just how many
ways can only be learned from a perusal of other portions of this
volume, especially those dealing with his high frequency work.
Certain laws govern the action or effects produced by a condenser when
connected to an electric circuit through which an alternating or in
general an undulating current is made to pass. Some of the most
important of such effects are as follows: First, if the terminals or
plates of a condenser be connected with two points of a circuit, the
potentials of which are made to rise and fall in rapid succession, the
condenser allows the passage, or more strictly speaking, the
transference of a current, although its plates or armatures may be so
carefully insulated as to prevent almost completely the passage of a
current of unvarying strength or direction and of moderate electromotive
force. Second, if a circuit, the terminals of which are connected with
the plates of the condenser, possess a certain self-induction, the
condenser will overcome or counteract to a greater or less degree,
dependent upon well-understood conditions, the effects of such
self-induction. Third, if two points of a closed or complete circuit
through which a rapidly rising and falling current flows be shunted or
bridged by a condenser, a variation in the strength of the currents in
the branches and also a difference of phase of the currents therein is
produced. These effects Mr. Tesla has utilized and applied in a variety
of ways in the construction and operation of his motors, such as by
producing a difference in phase in the two energizing circuits of an
alternating current motor by connecting the two circuits in derivation
and connecting up a condenser in series in one of the circuits. A
further development, however, possesses certain novel features of
practical value and involves a knowledge of facts less generally
understood. It comprises the use of a condenser or condensers in
connection with the induced or armature circuit of a motor and certain
details of the construction of such motors. In an alternating current
motor of the type particularly referred to above, or in any other which
has an armature coil or circuit closed upon itself, the latter
represents not only an inductive resistance, but one which is
periodically varying in value, both of which facts complicate and
render difficult the attainment of the conditions best suited to the
most efficient working conditions; in other words, they require, first,
that for a given inductive effect upon the armature there should be the
greatest possible current through the armature or induced coils, and,
second, that there should always exist between the currents in the
energizing and the induced circuits a given relation of phase. Hence
whatever tends to decrease the self-induction and increase the current
in the induced circuits will, other things being equal, increase the
output and efficiency of the motor, and the same will be true of causes
that operate to maintain the mutual attractive effect between the field
magnets and armature at its maximum. Mr. Tesla secures these results by
connecting with the induced circuit or circuits a condenser, in the
manner described below, and he also, with this purpose in view,
constructs the motor in a special manner.
[Illustration: FIG. 86.]
[Illustration: FIG. 88.]
[Illustration: FIG. 89.]
[Illustration: FIG. 87.]
[Illustration: FIG. 90.]
Referring to the drawings, Fig. 86, is a view, mainly diagrammatic, of
an alternating current motor, in which the present principle is applied.
Fig. 87 is a central section, in line with the shaft, of a special form
of armature core. Fig. 88 is a similar section of a modification of the
same. Fig. 89 is one of the sections of the core detached. Fig. 90 is a
diagram showing a modified disposition of the armature or induced
circuits.
The general plan of the invention is illustrated in Fig. 86. A A in this
figure represent the the frame and field magnets of an alternating
current motor, the poles or projections of which are wound with coils B
and C, forming independent energizing circuits connected either to the
same or to independent sources of alternating currents, so that the
currents flowing through the circuits, respectively, will have a
difference of phase. Within the influence of this field is an armature
core D, wound with coils E. In motors of this description heretofore
these coils have been closed upon themselves, or connected in a closed
series; but in the present case each coil or the connected series of
coils terminates in the opposite plates of a condenser F. For this
purpose the ends of the series of coils are brought out through the
shaft to collecting rings G, which are connected to the condenser by
contact brushes H and suitable conductors, the condenser being
independent of the machine. The armature coils are wound or connected in
such manner that adjacent coils produce opposite poles.
The action of this motor and the effect of the plan followed in its
construction are as follows: The motor being started in operation and
the coils of the field magnets being traversed by alternating currents,
currents are induced in the armature coils by one set of field coils, as
B, and the poles thus established are acted upon by the other set, as C.
The armature coils, however, have necessarily a high self-induction,
which opposes the flow of the currents thus set up. The condenser F not
only permits the passage or transference of these currents, but also
counteracts the effects of self-induction, and by a proper adjustment of
the capacity of the condenser, the self-induction of the coils, and the
periods of the currents, the condenser may be made to overcome entirely
the effect of self-induction.
It is preferable on account of the undesirability of using sliding
contacts of any kind, to associate the condenser with the armature
directly, or make it a part of the armature. In some cases Mr. Tesla
builds up the armature of annular plates K K, held by bolts L between
heads M, which are secured to the driving shaft, and in the hollow space
thus formed he places a condenser F, generally by winding the two
insulated plates spirally around the shaft. In other cases he utilizes
the plates of the core itself as the plates of the condenser. For
example, in Figs. 88 and 89, N is the driving shaft, M M are the heads
of the armature-core, and K K' the iron plates of which the core is
built up. These plates are insulated from the shaft and from one
another, and are held together by rods or bolts L. The bolts pass
through a large hole in one plate and a small hole in the one next
adjacent, and so on, connecting electrically all of plates K, as one
armature of a condenser, and all of plates K' as the other.
To either of the condensers above described the armature coils may be
connected, as explained by reference to Fig. 86.
In motors in which the armature coils are closed upon themselves--as,
for example, in any form of alternating current motor in which one
armature coil or set of coils is in the position of maximum induction
with respect to the field coils or poles, while the other is in the
position of minimum induction--the coils are best connected in one
series, and two points of the circuit thus formed are bridged by a
condenser. This is illustrated in Fig. 90, in which E represents one set
of armature coils and E' the other. Their points of union are joined
through a condenser F. It will be observed that in this disposition the
self-induction of the two branches E and E' varies with their position
relatively to the field magnet, and that each branch is alternately the
predominating source of the induced current. Hence the effect of the
condenser F is twofold. First, it increases the current in each of the
branches alternately, and, secondly, it alters the phase of the currents
in the branches, this being the well-known effect which results from
such a disposition of a condenser with a circuit, as above described.
This effect is favorable to the proper working of the motor, because it
increases the flow of current in the armature circuits due to a given
inductive effect, and also because it brings more nearly into
coincidence the maximum magnetic effects of the coacting field and
armature poles.
It will be understood, of course, that the causes that contribute to the
efficiency of condensers when applied to such uses as the above must be
given due consideration in determining the practicability and efficiency
of the motors. Chief among these is, as is well known, the periodicity
of the current, and hence the improvements described are more
particularly adapted to systems in which a very high rate of alternation
or change is maintained.
Although this invention has been illustrated in connection with a
special form of motor, it will be understood that it is equally
applicable to any other alternating current motor in which there is a
closed armature coil wherein the currents are induced by the action of
the field, and the feature of utilizing the plates or sections of a
magnetic core for forming the condenser is applicable, generally, to
other kinds of alternating current apparatus.
CHAPTER XXII.
MOTOR WITH CONDENSER IN ONE OF THE FIELD CIRCUITS.
If the field or energizing circuits of a rotary phase motor be both
derived from the same source of alternating currents and a condenser of
proper capacity be included in one of the same, approximately, the
desired difference of phase may be obtained between the currents flowing
directly from the source and those flowing through the condenser; but
the great size and expense of condensers for this purpose that would
meet the requirements of the ordinary systems of comparatively low
potential are particularly prohibitory to their employment.
Another, now well-known, method or plan of securing a difference of
phase between the energizing currents of motors of this kind is to
induce by the currents in one circuit those in the other circuit or
circuits; but as no means had been proposed that would secure in this
way between the phases of the primary or inducing and the secondary or
induced currents that difference--theoretically ninety degrees--that is
best adapted for practical and economical working, Mr. Tesla devised a
means which renders practicable both the above described plans or
methods, and by which he is enabled to obtain an economical and
efficient alternating current motor. His invention consists in placing a
condenser in the secondary or induced circuit of the motor above
described and raising the potential of the secondary currents to such a
degree that the capacity of the condenser, which is in part dependent on
the potential, need be quite small. The value of this condenser is
determined in a well-understood manner with reference to the
self-induction and other conditions of the circuit, so as to cause the
currents which pass through it to differ from the primary currents by a
quarter phase.
Fig. 91 illustrates the invention as embodied in a motor in which the
inductive relation of the primary and secondary circuits is secured by
winding them inside the motor partly upon the same cores; but the
invention applies, generally, to other forms of motor in which one of
the energizing currents is induced in any way from the other.
Let A B represent the poles of an alternating current motor, of which C
is the armature wound with coils D, closed upon themselves, as is now
the general practice in motors of this kind. The poles A, which
alternate with poles B, are wound with coils of ordinary or coarse wire
E in such direction as to make them of alternate north and south
polarity, as indicated in the diagram by the characters N S. Over these
coils, or in other inductive relation to the same, are wound long
fine-wire coils F F, and in the same direction throughout as the coils
E. These coils are secondaries, in which currents of very high potential
are induced. All the coils E in one series are connected, and all the
secondaries F in another.
[Illustration: FIG. 91.]
On the intermediate poles B are wound fine-wire energizing coils G,
which are connected in series with one another, and also with the series
of secondary coils F, the direction of winding being such that a
current-impulse induced from the primary coils E imparts the same
magnetism to the poles B as that produced in poles A by the primary
impulse. This condition is indicated by the characters N' S'.
In the circuit formed by the two sets of coils F and G is introduced a
condenser H; otherwise this circuit is closed upon itself, while the
free ends of the circuit of coils E are connected to a source of
alternating currents. As the condenser capacity which is needed in any
particular motor of this kind is dependent upon the rate of alternation
or the potential, or both, its size or cost, as before explained, may be
brought within economical limits for use with the ordinary circuits if
the potential of the secondary circuit in the motor be sufficiently
high. By giving to the condenser proper values, any desired difference
of phase between the primary and secondary energizing circuits may be
obtained.
CHAPTER XXIII.
TESLA POLYPHASE TRANSFORMER.
Applying the polyphase principle to the construction of transformers as
well to the motors already noticed, Mr. Tesla has invented some very
interesting forms, which he considers free from the defects of earlier
and, at present, more familiar forms. In these transformers he provides
a series of inducing coils and corresponding induced coils, which are
generally wound upon a core closed upon itself, usually a ring of
laminated iron.
The two sets of coils are wound side by side or superposed or otherwise
placed in well-known ways to bring them into the most effective
relations to one another and to the core. The inducing or primary coils
wound on the core are divided into pairs or sets by the proper
electrical connections, so that while the coils of one pair or set
co-operate in fixing the magnetic poles of the core at two given
diametrically opposite points, the coils of the other pair or
set--assuming, for sake of illustration, that there are but two--tend to
fix the poles ninety degrees from such points. With this induction
device is used an alternating current generator with coils or sets of
coils to correspond with those of the converter, and the corresponding
coils of the generator and converter are then connected up in
independent circuits. It results from this that the different electrical
phases in the generator are attended by corresponding magnetic changes
in the converter; or, in other words, that as the generator coils
revolve, the points of greatest magnetic intensity in the converter will
be progressively shifted or whirled around.
Fig. 92 is a diagrammatic illustration of the converter and the
electrical connections of the same. Fig. 93 is a horizontal central
cross-section of Fig. 92. Fig. 94 is a diagram of the circuits of the
entire system, the generator being shown in section.
Mr. Tesla uses a core, A, which is closed upon itself--that is to say,
of an annular cylindrical or equivalent form--and as the efficiency of
the apparatus is largely increased by the subdivision of this core, he
makes it of thin strips, plates, or wires of soft iron electrically
insulated as far as practicable. Upon this core are wound, say, four
coils, B B B' B', used as primary coils, and for which long lengths of
comparatively fine wire are employed. Over these coils are then wound
shorter coils of coarser wire, C C C' C', to constitute the induced or
secondary coils. The construction of this or any equivalent form of
converter may be carried further, as above pointed out, by inclosing
these coils with iron--as, for example, by winding over the coils layers
of insulated iron wire.
[Illustration: FIGS. 92 and 93.]
[Illustration: FIG. 94.]
The device is provided with suitable binding posts, to which the ends of
the coils are led. The diametrically opposite coils B B and B' B' are
connected, respectively, in series, and the four terminals are connected
to the binding posts. The induced coils are connected together in any
desired manner. For example, as shown in Fig. 94, C C may be connected
in multiple arc when a quantity current is desired--as for running a
group of incandescent lamps--while C' C' may be independently connected
in series in a circuit including arc lamps or the like. The generator in
this system will be adapted to the converter in the manner illustrated.
For example, in the present case there are employed a pair of ordinary
permanent or electro-magnets, E E, between which is mounted a
cylindrical armature on a shaft, F, and wound with two coils, G G'. The
terminals of these coils are connected, respectively, to four insulated
contact or collecting rings, H H H' H', and the four line circuit wires
L connect the brushes K, bearing on these rings, to the converter in the
order shown. Noting the results of this combination, it will be observed
that at a given point of time the coil G is in its neutral position and
is generating little or no current, while the other coil, G', is in a
position where it exerts its maximum effect. Assuming coil G to be
connected in circuit with coils B B of the converter, and coil G' with
coils B' B', it is evident that the poles of the ring A will be
determined by coils B' B' alone; but as the armature of the generator
revolves, coil G develops more current and coil G' less, until G reaches
its maximum and G' its neutral position. The obvious result will be to
shift the poles of the ring A through one-quarter of its periphery. The
movement of the coils through the next quarter of a turn--during which
coil G' enters a field of opposite polarity and generates a current of
opposite direction and increasing strength, while coil G, in passing
from its maximum to its neutral position generates a current of
decreasing strength and same direction as before--causes a further
shifting of the poles through the second quarter of the ring. The second
half-revolution will obviously be a repetition of the same action. By
the shifting of the poles of the ring A, a powerful dynamic inductive
effect on the coils C C' is produced. Besides the currents generated in
the secondary coils by dynamo-magnetic induction, other currents will be
set up in the same coils in consequence of many variations in the
intensity of the poles in the ring A. This should be avoided by
maintaining the intensity of the poles constant, to accomplish which
care should be taken in designing and proportioning the generator and in
distributing the coils in the ring A, and balancing their effect. When
this is done, the currents are produced by dynamo-magnetic induction
only, the same result being obtained as though the poles were shifted by
a commutator with an infinite number of segments.
The modifications which ar
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