Tesla's New Alternating Motors

Friday, October 10, 1890
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Ang.6,1890.] THE ELECTRICAL ENGINEER. ,gg TESLA'S NEW ALTERNATING MOTORS. Fonvspme time past Mr. Nikola Tesla, whose revious work 'inialteriiating-cnrreritjmotorsis well known, has been engaged upon the study of these machines in order to de- velop effieicnt methods for operating them on two wires instead of three, and still without the use of a commutator. The general principle upon which these machines are de- signed xs based on the weIl~known fact that if a magnetic core, even if laminated, be wound with a. coil and a cur- rent be sent through, thc magnetization of the entire core does not immediately ensue, the magnetizing effect not be- llki I-‘wwf .K I Il F@ F Fm. 1.--Tests Anraunarruc Moron. ing exhibited in all parts simultaneously. This Mr, Tesla attributes to the 'fact that the action of the current is to energize first those laminm or parts of the core nearest the surface and adjacent to the exciting coil, and from thence the action progresses towards the interior. A certain in- terval of time, therefore, elapses between the manifestation layers of the core. ,Let us consider now th this core at any point, as e magnetic conditions existing in b, at or near the centre, and any V Q sl»§f;2.é\2§liri s t \ in r F i i i \ ®\\§ ‘ '_\\\W ,N gl fn' 47 » l 2 yn, ,,./ § §%~ ‘ l QQ” l|| 7 , 7 ,,,,,,/,,,',!i Z ¢\'=‘a: i \\¢\ \ tt. r,.,,,.,mz Fm. 3.-Team ALTERNATXNG Moron. other point, as a, nearer the surface. According to Mr. Tesla, when a current impulse is started in the magnetizing coil,_Y, the section, at a, being close to the coil, is im- mediately energized, while the section, at b, which, to use a convenient expression, is “protected " by the r § Flo. 4.-Tasna Anrnunarmc Moron. of magnetism in the external and the internal sections or A H il If the core be thin or of small mass this effect may be Q lil ga inappreciable, but in the case of a thick core, or even of a _ *" comparatively thin one, if the number of alternation be very ww _ great, the time interval occurring between the manifesta- ‘“l¥ \ tions of magnetism in the interior of the core and in those ,wlimi-, ® @K rl lu @W`lll\it o "4 hi _ stan. ,-,ai ri F G G F D 5 . Flo. 2.-Tnsna Anranuarmo MOTOR. parts adjacent to the coil is more marked, and in the con- struction of such apparatus as motors which are designed to be run by alternating currents, Mr. Tesla has found it desirable, and even necessary, to give due consideration to this phenomenon and to make special provisions in order to obviate its consequences. On the other hand, by taking advantage of' this very ac- tion or effect, and, by renderin it more pronounced, Mr. Tesla utilizes it in the operation 0? motors in general. This be effects by constructing a field in which the parts of the core that exhibit at different intervals of time the mag- netic effect imparted to them by _alternating currents in an energizing coil are so placed with relation to a rotating armature as to exert thereon their attractive edect succes- sively in the order of their magnetization. By this means there i secured a result similar to that which Mr. Tesla has heretofore attained in the previous types of his motor, in which, by means of one or more nltcrnnting currents, he produces a rotation or progression of the magnetic poles or points of maximum attraction of the field of force. The general principle involved in the action above men- tioned is illustrated in the simple motor shown in Fig. 1. Here x represents a large iron core composed of a number of sheets or laminae of soft iron or steel._ Surrounding this core is a coil, Y, which i§ connected with a source, E, of rapidly varying currents. intervening sections or layers between a and b, does not at once exhibit its magnetism. However, as the magnet- ization of a increases, b becomes also adected, reaching finally its maximum strength some time later than a. cs new ¢ l lg, (° WWWIH j@El L FIG. 5.-Testa AL'rauNA'rrNo Moron. W .fy ,Q #Wu !` ,!`l. I i e B G 'u,,u_;¢-r al Q 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 subse- quent weakening of b. Assuming the current to be an alternating one, a will now be reversed while I1 still con- tinues of the polarity first imparted. This action contin-

:=Ei` Jwllllllllll 140 THE ELECTRICAL ENGINEER. [Aug.6,1890. ues, the magnetic condition of b following that of a in the manner above described. ` If an armature, for instance, a simple disk mounted to rotate freely on an axis, be brought into proximity to the core, a movement of rotation will be imparted to the disk, the direction depending upon its position relatively to the core, the tendency being to turn the position of the disk nearest to the core from a to b, as indicated in Fig. l. This action or principle of operation has been embodied in a practicable form of motor, which is illustrated in Fig. 2. llere A represents 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 11,8 and C, and they are similarly made with a straight portion e, around which the energizing coil is wound, a curved arm or extension c and an inwardly projecting pole cl. Each core is made of two parts n ix, 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. These cores are Wound with coils D, which are connectediin the same circuit either in parallel or series and supplied with an alternating current by a generator E represented diagramatically. Between the cores or their polar extensions is mounted an armatnre F wound with magnetizing coils G that are closed upon them- A // Ya 5 sn 17) @ >» z c T1 | »-3 za Ui C* > P :- Pi :a W z > 2 z ra 3 3 o F s X 3 / }l§|§l{ ::::s-EE D ni? ' 40" .\gg,/ if -= ..=:§===s= selves, similar tc those in the older types of Mr. 'l'esla’s motors. _ The operation of the motor is as follows: When a cur- rent impulse or alternation is sent through the coils D, the sections n n 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 mag- netizing influence of the coil by the interposed layers of iron n D. - _ As the magnetism of ix n increases, however, the sections 0 are also energized, but they do not attain their maximum strength until acertain time subsequent to the exhibition hy the sections iz ri of their maximum. _ Upon the weakening of the current the magnetic strength of rx 11. lirst diminishes while the sections C have still their maximum strength; but as n n continue to weaken, the interior sections are similarly weakened. _ n n may then begin to exhibit an opposite polarity, which is followed later by a similar change on c, and this action continues. n is and c may, therefore, be considered as separate field magnets, being extended so as to act on ‘the armature in the most ellicient positions, and the effect is snmlar to that in Mr. 'l`esla’s other forms of motor, viz., a rotation or progression of the maximum points of the field of force. /\ny arlnature, 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. ~ In following out the ideas stated above, Mr. Tesla has , applied them to a 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 of their magnetic attraction or effect. This has already been applied to the operation of Mr. '1"esla’s three-wire motors. In the present instance Mr. Tesla employs a motor with two sets of energizing or Held magnets, each wound with coils connected with a source of alternating currents, but forming two separate paths or circuits. The magnets of one set are irotccted to a certain extent from the energizing action of the current hy means of a magnetic shield or screen of laminated iron interposed between the magnet and its energizing coil. The shield is properly adapted to the conditions of par- ticular 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 thc current. By this means it will he seen that 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 a practically economical difference of magnetic phase may readily be secured. The nature and operation of this motor will be readily un- derstood by reference to the accompanying illustration. The engraving, Fig. 4, shows the simplest form of this type of machine. The cores rx form one set of magnets and are energized by coils D, while the cores C, forming the other set, are energized by coils E, and the coils are con~ nected in series with one another, in two derived or branched circuits F G respectively. Each coil E, it will be noted, is surrounded by amagnetic shield H, which is composed of an annealed insulated or oxidized iron wire wound on the coils in the manner indi~ cated, so as to form a closed ma netie circuit around the coils and between the same and tie magnetic cores 0. Between the pole pieces or cores B c is mounted the armature of the closed-circuit coil type. The operation resulting from this' arrangement is as follows : If a current impulse bs 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 n. Thelirst effect is to effectively retard 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 u. As the increasing electromotive force then urges more current through the coils iz, 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 become magnetized, developing their maximum effect afteran interval of time subsequent to the similar mani~ festation of strength in the ,other set of magnets, the extent of which may be arbitrarily determined by the thickness of the shield lil, and other well known conditions. From the above it willibe seen that, the apparatus or device 'acts in two ways. First, by retarding the current, and secom1‘by retarding the magnetization of one set of cores, from which its effectiveness will readily be seen. ' Many modilfications of the principle hers embodied have been made by Mr. 'l`esla, one only more of which we may notice here. This is illustrated in Fig. 5, andis similar in all respects to thatabove described, except that the iron wire n, which is wrapped around the coils s, is in this case con- nected in series with the coils n. The iron wire coils are connected and 'wound so as to have little or no self-iuduc~ tion, an`d,being added to the resistance of the circuit F, the action of the current in that circuit will be accellera- led while in the other cii'euit G it will be retarded. 'Still another type of motor constructed by Mr. Tesla is one with a Held magnet having two sets of poles or»in~ wardly projecting cores and placed side by side so as prac- tically to form two fields of force, and alternately ar-

Aug.s,1s9<>_] THE ELECTRIC ranged, that is to say, with the poles of one set or iield op- posite the spaces between the other. The free ends of one set of poles are then connected by means of laminated iron bands or bridge pieces of considerably smaller cross-section than the cores themselves, so that the cores all form parts of complete magnetic circuits. \’Vlien the coils on eacl\ set of magnets are connected in multiple circuits from an alternating machine electro- motive forces are set up in 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 \Vl1iGll rctards the current, permitting at the be- ginning 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, nmgnetizing the poles on which they are wound. As soon, liowever, as the laminated bridges become satu- rated 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, pro- duce rotation of the armatnre. 'l‘he construction by which this is accomplished is shown in the accompanying engravings, Figs. 6 and 7. The frame of the motor A, is 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 n and o. To adapt them to the requirements of this particular case, these pole pieces are out of linc with one another, those marked n surrounding one end of the arma- ture, and the others o the opposite end, and they are ar- ranged alternately; that is to say, the pole pieces ol' one are set in line with the spaces between those of the other sets. 'l‘he pole pieces c are connected or shnnted by bridge pieces n. 'l‘he coils F and G are connected in series, respectively, in two circuits which are branches of a circuit from an alternatingmachine, and they are so wound that the cir- cuit of coils o will have a hlgbcr 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 cur- rent up to a predetermined strength, so that when satu- rated by such current and unable to carry more lines of force than such a current produces, they will, to no further apprcciable extent, interfere with the development by a stronger current of free magnetic poles at the ends of the cores o. In such a motor the current is so retarded in the coils o and thc manifestation of the free magnetism in the poles C is delayed beyond the periods of maximum magnetic effect in poles rs. The result is that a strong torque is produced and the motor operates with approximately the power developed in a motor of this kind energized by independ- ently gcnerated currents differing by a full quarter phase. TESLNS TRANSFORMER FOR MOTOR WORK AND FOR CONSTANT CURRENT. IN the early forms of alternating motor brought out by Mr. Tesla the construction embodied a series of coils trav- ersed by currents differing a. quarter phase from one another. This has in some forms required three wires from the generator to the motor, but in order to avoid this Mr. Tesla has recently constructed a converter specially de- signed to be used in connection with his motor, and in which the difference of phase required is spontaneously brought about. This converter also possesses the valuable property that it operates with a constant current for all loads imposed upon the secondary. In transformers as at present constructed it is found that the eloctroxnotive force of the secondary very nearly coin- AL ENGINEER. 141 cides with that of the primary, being, however, of oppo- site sign. At the same time the currents, both primary and secondary, lag behind their respective electromotive forces, but as this lag is practically the same in the case of each, it follows that the maximum and minimum of the primary and secondary currents will nearly coincide, but differ in sign or direction, provided the secondary be not loaded, or if it contain devices having thc property of sclf_ induction. _ On the other hand, the lag of the primary behind the impressed electromotive force may be diminished by load- lng the secondary with a non-inductive or dead resistance, such as incandescent lamps, whereby the time interval be- D B l I B E i I 2 p 1 1 ,, f:f nrT71t.t»,i B I 5 sr.sL.i,f..s;|'. Fic. 1.-Nnw Tests Consrsrrr CURRENT Tnsnsrommn. tween the maximum or the minimum periods of the pri- mary and secondary currents is increased. This time in- terval, however, is limited, and the results obtained by phase difference in the operation of such devices as Mr. Tesla’s alternating current motors can only be approxi- mately realizcd by such means of producing or securing this difference, as above indicated. For it is desirable in such cases that there should exist between the primary and sec- ondary currents, a difference of phase of 90 degrees, or in other words, the currcnt in one circuit should be maximum when that in the other circuit is minimum. To more nearly and perfectly attain to this condition Mr. Tesla secures an increased retardation of the secondary censimnn E B D m \ , _ 1. _ ~<-“~~~ F _ & i ¢` °~~s r ~ >..»»|.n saw" 2 B M ®* ° ° B aussi.,-_.mid Fm. 2.~Naw 'Fuses Consranr Gtmnnirr Tnsnsronnan. current in the following manner 1 Instead of bringing thc primary and secondary coils or circuits of a transformer into the closest possible relations, as has hitherto been done, he protects in a measure the secondary from the in- ductive eifect of the primary by surrounding either the primary or the secondary with a comparatively thin mag- netic shield or screen. Under these conditions, as long as the primary current has a small value thc shield protects the secondary, but as soon as the primary current has reached a certain strength, which is arbitrarily determined, thc protecting magnetic shield becomes saturated and theinvluctive action upon the secondary begins. lt results, therefore, that the secondary current begins to dow at a certain fraction of a period later than it would without the interposed shield, and since this retardation may bc obtained without necessarily re-