Fig. 28, 29.Fig. 28.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, letCrepresent a cylindrical armature core wound longitudinally with insulated coilsA A, which are connected up in series, the terminals of the series being connected to collecting-ringsa aon the shaftG. By means of this shaft the armature is mounted to rotate between the poles of an annular field-magnetD, formed with polar projections wound with coilsE, that magnetize the said projections. The coilsEare included in the circuit of a generatorF, 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 armatureCa second set of coilsB Bintermediate 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 coilsBare connected, also, in series and to two connecting-rings, secured generally to the shaft at the opposite end of the armature.
Fig. 30.Fig. 30.Fig. 31.Fig. 31.
Fig. 30.Fig. 30.
Fig. 31.Fig. 31.
The motor shown in Fig. 29 has an annular field-magnetH, with four pole-pieces wound with coilsI. 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 Jare magnets disposed in a circle and wound with coilsK, which are in circuit with a generator whichsupplies the current that maintains the field of force. In the usual construction of these machines the armature-conductorLis carried by a suitable frame, so as to be rotated in face of the magnetsJ 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 conductorCis 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 conductorsM, 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 conductorLit increases in conductorM, 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, andK'the coils thereon.L'is one of the armature-conductors andM'the other.
Fig. 32 shows in diagram other forms of machine. The generatorNin this case is shown as consisting of a stationary ringO, wound with twenty-four coilsP P', alternate coils being connected in series in two circuits. Within this ring is a disc or drumQ, with projectionsQ'wound with energizing-coils included in circuit with a generatorR. By driving this disc or cylinder alternating currents are produced in the coilsPandP', which are carried off to run the several motors.
The motors are composed of a ring or annular field-magnetS, wound with two sets of energizing-coilsT T', and armaturesU, having projectionsU'wound with coilsV, all connected in series in a closed circuit or each closed independently on itself.
Suppose the twelve generator-coilsPare wound alternately in opposite directions, so that any two adjacent coils of the same set tend to produce a free pole in the ringObetween them and the twelve coilsP'to be similarly wound. A single revolution of the disc or cylinderQ, the twelve polar projections of which are of opposite polarity, will therefore produce twelve current impulses in each of the circuitsW W'. Hence the motorX, whichhas sixteen coils or eight free poles, will make one and a half turns to the generator's one. The motorY, with twelve coils or six poles, will rotate with twice the speed of the generator, and the motorZ, 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 motorX, 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 ofpoles one-half, and thereby doubling the speed of any given motor.
Fig. 32.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 brushesd d' g g'bear upon these rings, respectively, and convey the currents through the two independent line-circuitsM 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 coilsJ J', included, respectively, in the circuitsM 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 armatureHof 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, asN N, wound on a ring or annular core is connected to one circuit, asM', and the other primary coils,N N', to the circuitM. The secondary coilsK K'may then be utilized for running groups of incandescent lampsP P'.
Fig. 33.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-ringsb c, respectively, while theother ends are both connected to a ring,a. Collecting-brushesb' c'bear on the ringsb c, respectively, and conductorsL Lconvey the currents therefrom through the coilsEandEof the generator.L'is a common return-wire to brusha'. Two independent circuits are thus formed, one including coilsCof the exciter andE Eof the generator, the other coilsC'of the exciter andE'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 coilsF 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-coilsF 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 casesupon 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.
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°, there will be no current delivered.
Fig. 34 is a view in side elevation of the regulator. Fig. 35 is a broken section on linex xof 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.
Arepresents a frame of iron.B Bare the cores of the inducing or primary coilsC C.Dis 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 coreEto be turned to and held at any desired point. A handle,G, secured to the projecting end of the shaftD, is provided for this purpose.
Fig. 34.Fig. 34.Fig. 35.Fig. 35.
Fig. 34.Fig. 34.
Fig. 35.Fig. 35.
In Fig. 36 letHrepresent an ordinary alternating current generator, the field-magnets of which are excited by a suitable source of current,I. LetJdesignate an ordinary form of electromagnetic motor provided with an armature,K, commutatorL, and field-magnetsM. 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 coreE.
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.
Fig. 36.Fig. 36.
To vary the speed of the motor to any rate between the minimum and maximum rates, the coreEand coilsFare turned in either direction to an extent which produces the desired result, for in its normal position the convolutions of coilFembrace 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 coilFout 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 coilFwill continue to diminish in proportion to the angle at which the coilFis turned until, after passing through an angle of ninety degrees, the convolutions of the coil will be at right angles to those of coilsC 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 coilFa 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.
Fig. 37.Fig. 37.
It may also be stated that the coreEis 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 coilFbe turned through a half-revolution, the position of its convolutions relatively to the two coilsC Cand 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, letPrepresent a Tesla generator having two independent coils,P'andP'', on the armature, andTa diagram of amotor having two independent energizing coils or sets of coils,R R'. One of the circuits from the generator, asS' S', includes one set,R' R', of the energizing coils of the motor, while the other circuit, asS 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 coilFof the regulator is turned. The motor will also be reversed by reversing the position of the coil with reference to the coilsC 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 coilsC Cor coilFmay 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.
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.
Fig. 38, 39 and 40.Figs.38, 39 and 40.
Referring to Fig. 38, letAdesignate the field-magnets of a motor, the polar projections of which are wound with coilsB Cincluded in independent circuits, andDthe armature with polar projections wound with coilsEclosed upon themselves, the motor in these respects being similar in construction to thosedescribed 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 generatorG.
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 barsF F'is the contact 2, which forms one terminal of the circuit through coilsC, and the contact 4, which is one terminal of the circuit through coilsB. The opposite end of the wire of coilsCis connected to the wireLor barF', and the corresponding end of coilsBis connected to wireL'and barF; hence if the bars be shifted so as to bear on contacts 2 and 4 both sets of coilsB Cwill be included in the circuitL L'in multiple arc or derivation. In the path of the leversF 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 coilsBandCwill be connected in multiple arc or derivation to the circuitL L', and will include the resistance and self-induction coil respectively. A third position of the switch is that in which the leversFandF'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 resistanceIin one and the self-induction coilJin 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 coilsIandJ, 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 circuitsBorCconnected 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 projectionsDwound with closed coilsE. 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-circuitsB C, which include alternate field-coils, are connected to the terminals in the following order: One end of circuitCis connected to contact 9 and to contact 5 through a dead resistance,I. One terminal of circuitBis 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, asF, 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 leverF'on contact 8 the current divides between the two circuitsB 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 circuitsBandCin 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. LetGin this figure represent an ordinaryalternating-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 coilsB C, which are connected in series, and an armature with polar projectionsDwound with closed coilsE 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 circuitsLandL'. 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-switchesP 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.
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 coilsA Bat right angles. The shaft of the armature carries three collecting or contact ringsC D E. (Shown, for better illustration, as of different diameters.)
One end of coilAconnects to one ring, asC, and one end of coilBconnects with ringD. The remaining ends are connected to ringE. Collecting springs or brushesF G Hbear upon the rings and lead to the contacts of a switch, to be presently described. The field-coils have their terminals in binding-postsK K, and may be either closed upon themselves or connected with a source of direct currentL, by means of a switchM. The main or controlling switch has five contactsa b c d eand two leversf g, pivoted and connected by an insulating cross-barh, so as to move in parallelism. These levers are connected to the linewires from a source of alternating currentsN. Contactais connected to brushGand coilBthrough a dead resistanceRand wireP. Contactbis connected with brushFand coilAthrough a self-induction coilSand wireO. Contactscandeare connected to brushesG F, respectively, through the wiresP O, and contactdis directly connected with brushH. The leverfhas a widened end, which may span the contactsa b. When in such position and with levergon contactd, 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.
Fig. 41.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 leversf gresting on pointsc 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.
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.
Figs. 42, 43 and 44.Figs.42, 43 and 44.
A Bin Fig. 42 indicate the two energizing circuits of a motor, andC Dtwo circuits on the armature. Circuit or coilAis connected in series with circuit or coilC, and the two circuitsB Dare similarly connected. Between coilsAandCis a contact-ringe, forming one terminal of the latter, and a brusha, forming one terminal of the former. A ringdand brushcsimilarly connect coilsBandD. The opposite terminals of the field-coils connect to one binding posthof the motor, and those of the armature coils are similarly connected to the opposite binding postithrough a contact-ringfand brushg. 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 resistanceRis shown in one of these circuits, and in the other a self-induction coilS. When an alternating current is passedthrough 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 factthat 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 isx, 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 alsox.