Letter: Tesla's New Alternating Motors

Wednesday, September 24, 1890
Archived Page: 

346 THE ELECTRI three-wire system oliers to the alternating system relatively greater advantages, than the three-wire direct possesses over the two-wire. Perhaps, if the writer in Industries would have taken allthis in consideration, he would have been less hasty in his conclusions. NIKOLA -msn. New Yann, Sept. 17. mo. CAL ENGINEER. ISBN-24,1S90~

S°P¢~24,1990-] THE ELECTRICAL ENGINEER. 345 lead me too far-an arrangement was shown in THE ELEUTHICAL Exomsaa, about which the writer in Industries says 1 “A ring of laminated iron is wound with a secondary. It is then encased in iron laminated in the wrong direction and the primary is wound outside of this. The layer of iron between the 'rimary and sec- ondary is supposed to screen the coil. Of course it cannot do so, such a thing is unthinkable.” This reminds me of the man who had committed some oEense and engaged the services of an attor- ney. “Tbeiy cannot commit you to prison for that," said the attorney. inally the man was imprisoned. Be sent for the at- iomey. “ Sir," said the latter, “ I tell you they cannot imprison you for that." “ But, sir,” retorted the prisoner, “ they have imprisoned me." It may not screen, in the opinion of the writer in ndustries, but just the same it does. According to the arrange- ment the principal etfect of the screen may be either a retarda- tion of the action of the primary current upon the secondary cir- cuit or a deformation of the secondary current wave with similar results for the pur oses intended. In the arrangement referred to by the writer in yizrlnstries he seems to be certain that the iron layer acts like a clicking coil; there again he is mistaken; it dues not act like a choking coil, for then its capacity for maintaining constant current would be very limited. But it acts more like a magnetic shunt in constant current transformers and dynamus, us, in my opinion, it ought to nct. There are a good mnny more things to bo said about the re- marks contained in Industries. In regard to the magnetic time lag the writer says: " If a har of iron has a. coil at one end, and if the core is perfectly laminated, on starting a current in the coil the induction ull along the iron corresponds to the excitation at that instant, unless there is a. microscopic time lag, of which there is no evidence.” Yet a motor \vas described, the very operation of which is dependent on the time lag of magnetization of the different parts of a core. It is true the writer uses the term “per- fectly laminated ” (which, by the way, I would like him to ex- plain), but if he intends to make such a “ perfectly laminated " core I venture to say there is trouble in store for him. From his remarks I see that the writer completely overlooks the import- ance of the size of the core and of thc number of the alternations pointed out; he fails to see the stress laid on tba saturation of the screen, or shunt, in some of the cases described; he does not seem to recognize the fact that in the cases considered the formationof current is reduced as far as practicable in the screen, and that the same, therefore, so far as its quality of screening is concerned, has no role to perform as a comluclor. I also see that he would want considera le information about the time lag in tho magnet- ization of the different parts of it core, and an explanation why, in the transformer he refers to, the screen is laminated in the wrong direction, etc.-but the elucidation of all these points \vould require more time than I am able to devote to the subject. It is distressing to End all this in the columns of u. leading technical journal. ln conclusion, the writer shows his true colors by making the following withering ~remarks: “ It is questionable whether the Tesla motor will ever be a success. Such motors will go round, of course, and will give outputs, but their efficiency is doubtful; and if they need three-wire circuits and special generators there is no object in using them, as a direct current motor can be run instead with advantage.” No man of broad views will feel certain of the success of an invention, however good and original, in this period of feverish activity, when every day may bring new ami unforseen develop- ments. At the pace \ve nre progressing the permanence of all our apparatus it its present forms becomes more and more roblem~ aticsl. It is impossible to foretell what type of motor \vili)crystal- ize out of the united eiiorts of many able men; but it is my con- viction that at no distant time al. motor having commutstor and brushes will be looked upon as an nntiquuled iiece of mechanism, Just how much the last quoted remarks of tire writer of Indus- tries-considering the present state of the art-are justified, I will endeavor to show in a few lines. First, take the transmission of power in isolated places. A C888 frequently occurring in practice nnd attrnctin ' more and more the attention of engineers is the transmission ik large powers at considerable distances. In such u cnsu thc power is very likely to be cheap, nnd the cardinal requirements are then the reduction of the cost of the leads, cheapness of construction and mainte- nance of machinery and constant speed of the motors. Suppose a loss of only 225 por cent. in thc lends, at full loud, he allowed. If u direct cilrrent motor he used, thorn will bn, hcaiilus other dif- licultivs, considornhln vnrintiun in thu s iced of thu motor-uvun if the current is supplied from o series dynamo-so much so tlint the motor may not be well adapted for many pnrposm, for instance, in cases where direct current transformation is contem- plated \vith the object of running lights or other devices at non- staint potential. It is true that the condition may be bettered by employing proper regulating devices, but those will only further complicate the already complex system, and in all irobability fail to secure such perfection as will be desired. lln usin an ordinary single-circuit alternate current motor the disadvaniige is that the motor has no starting torque and that, for e ual weight, its output and efficiency are more or less Iiielow that of a direct current motor. If, on the contrary, the arma- turo of any alternator or direct current machine-large, low- speed, two-pole machines will give the best results-is wound with two circuits, a. motor is at once obtained which possesses suf- ficient torque to start under considerable load; it runs in absolute synchronism with the generator-an advantage much desired and hardly ever to be attained with regulating devices; it takes cur- rent in proportion to the load, and its plant etbciency within a few per cent. is ual to that of a direct current motor of the same size. It wgllbe able, however, to perform more work than a direct currentmotor of the same size, first, because there will he no change of speed, even if the load be doubled or tripled, within the limits of available generator power; and, secon , because it can be run at a higher electromotive force, the commutator and the complication and dit1icultie.s;it involves in the construction and operation of the generators and motors being eliminated from the system. Such asystem will, of course, require three leads, but since the plant efficiency is practically equal to that of the direct current system, it wil require the same amount of copper which would be re uired in the latter system, and the disadvan- tage of the third (iead will be comparatively small, if any, for three leads of smaller size ma erhaps bs more convenient to place than two larger leads. %Viien more machines have to be used there may be no disadvantage whatever connected with the third wire; however, since the simplicity of the generators and motors allows the use of higher electromotive forces, the cost of the leads may be reduced below the figure practicable with the direct current system. Considering all the practical advantages offered by such an al- ternating system, I am of an opinion quita contrary to that of the author ofthe article ln Imluslries, and think that it can quite successfully stand the competition of any direct current system, and this the more, the larger the machines built and the greater the distances. Another case frequently occurring in practice is the transmis- sion of small powers in numerous isolated places, such as mines, sto. In many of these cases simplicity and reliability of the apparatus are the principal objects. I believe that in many p aces of this kind my motor has so far proved a. perfect success. n such cases n type of motor is used possessing great starting torque, requiring for its operation only alternating current and having no sliding contacts whatever on the armatnre, this advan- tage over other types of motors being highly valued in such places. The lant efhciency of this form of motor is, in the present state of periection, inferior to that of the former form, but I am confident that improvements will be made ln that direction. Be- sides, plant edicieucy is in these cases of secondary importance, and in cases of transmission at considerable distances, it is no drawback, since the electromotive force may be raised as high as practicable on converters. I can not lay enough stress on this ad- vantageous feature of my motors, and should think that it ought to be fully appreciated by engineers,for to high electronxoiive forces we are surely coming, and if they must be used, then the flttest apparatus will be employed. I elieve that in the transf mission of power with such commutawrless machines, 10,000 volts, and even more, may be used, and I would be glad to see Mr. Fer- ranti’s enterprisesucceed. His work is in the right direction, and, ip] my opinion, it will be of great value for the advancement of t e art. As regards the supply of power from large central stations in cities or centres of manufacture, the above arguments are appli- cable, and I see no reason why the three-wire motor system should not be successful. In putting up such a station, the third wire would be but a very slight drawback, and the system possesses enough advantages to over-balance this and any other disudvnniago. But this question will be settled in the future, for as yet cuinpurativuly little has been done in that direction. oven with the direct current system. 'l`he plant etliciency of such a three-wire system would beincreased by using, in connection with the ordinary type of my motor, other types which not more like inert resistances. The plant efficiency of the whole system would, in all cases, be 'reater than that of each individual motor-if like motors are useii-owing to the fact that they \vould possess differ- ent self-induction, according to the load. The supply of power from lighting mains is, I believe, in the opinion of most engineers, limited to comparatively small powers, for obvious reasons. As the present systems are built on the two- wire plan, an etllcient two-wire motor without commutator is required for this purpose, and also for traction purposes. Alsrge number of these motors, embodying new principles, have been devised b me and are being constanlly perfectc . On lighting stations, however, my three-wire system may be advantageously carried out. A third wire may be run for motors and the old con- nections left undisturbed. The armntnres of the generators may be rewound, whereby the output of the machines will be increased about 35 per cent., or even more in machines with cast iron field magnets. If the machines me worked at the same capacity, this means an increased efliciency. If power is available at the station, the gain in current may be used in motors. Those who object to the third wire, may remember that the old two-wire direct system ls almost entirely superseded by the three-wire system, yet my

THE ELECTRICAL ENGINEER. [Sept-24,1B90~ LETTERS TO Tl-IE EDITOR. Notice to correspondents. We do not hold ourselves: mrpmmiblazfor llm opinimu rf our correrpamlem . Anonymous commvmtcalfions ammo be :zo/ire/L Tltc minor mpwyuuy requests f/ta: fra wmnnmwazio/if may be in-fwm up aa In-iz/ly amz ax mom w lite pain: fn 1m.<»img_ _ 4 In order lo facililafe rgferllwe, c0rl'a»1]mnvlell/x, 1U/tm 7'/5/'91'7'1llg (Il any lrllar 17rL'w.» only inmrerz wut amiga by mmti/ming l/te sm-ia: mmmf- af nm/L mm, :mil qr me page on wltialt U rippntrr. _ Skelcltea and draluinlyk fm' illuslmllmu shnulll be an sQ1a1‘r1/A pteres Q/` llaper. All cornmunicaliurw xfmlllfl he mlflresxed Enlrorc oi# 'l ur: ELl»:c'r|LlcAL Ennmxsn |50 Broadway, New York oil;/_ TESLA‘S NEW ALTERNATING MOTORS. [1B9.]-I hope you will allow me the privilege to say in the col- umns of your esteemed journal a. few words in regard to an article which appeared in Irtdlmlries of August 22, to which my attention has been called. In this article an attempt is made to criticise some of my inventions, notably those which you have described in your issue of August 6, \890. The writer begins by stating: “The motor depends on a shift- ing of the oles under certain conditions, a principle which has been alreadtul employed by Mr. A. \Vright in his alternating cur- rent meter.” This is no surprise to nie. It would rather have surprised me to learn that Mr. Wright has not 3/ct employed the principle in his meter, considering what, before its appearance, was known of my work on motors, and more particular y of that of Schallenberger on meters. It has cost me years of thought to arrive at certain results, by many believed to he unattainable, for which there are now numerous claimants, and tho number of those is rapidly increasing, like that of the colonels in the South after the war. The writer then good-naturedly explains the theory of action of the motive device in Wright‘s meter, which has greatly bene- Hted me, for it is so long' since I have arrived nt this, and sinh ilar theories, that I had almost forgotten it. Ile then says: “ Mr. Tesla has worked out some more or less complicated motors on this princi vle, but the curious point is that he has completely mis- understood the theory of the phenomena, and has got hold of the old fallacy of screening.” This may be curious, but how much more curious it is to iind that the writer in Industries has com- pletely misunderstoad everything himself. I like nothing better than just criticism of my work, even if it he severe, but when tho critic assumes a. certain “ Fétat c‘est moi “ air of unquestioned competency I want him to know what he is writing about. How little the writer in Industries seems to know about the matter is painfully apparent when he connects the phenomenon in \Vright's meter with the subject he has under consideration. His further remark, “He (Mr. Tesla) winds his secondary of iron instead of copper and thin ks the effect is produced magnetically," is illustra- tive of the care with which he has pcrused the description uf the devices contained in the issue of Tun Enncriucu. Enomsss above referred to. I take a motor having, say eight poles, and wrap the exciting coils of four alternate cores with fine insulated iron wire. When the current is started in these coils it encounters thc effect of the closed magnetic circuit and is retarded. 'l`he magnetic lines set up at the start close to the iron wire around the coils and no free poles appear at Hrst at the ends of the four cores. As the curront rises in the coils more lincs are set up, which cro\vd more and more in tho line iron wire until finally the same becomes satu- rated, or nearly so, when the shielding action of the iron wire ceases and free poles appear at the ends of the four protected cores. The eifect of the iron wire, as will be seen, is two-fold. First, it retards the energizing currcnt; and second, it delays the appearance of thefree poles. To produce a still greater dilference of phase in the magnetization of the protected and unprotected cores, I connect the iron wire surrounding the coils of the former in series with the coils of the latter, in which case, of course, the iron wire is preferably wound or connected differentially, after the fashion of the resistance coils in a bridge, so as to have no ap- preciable self-induction. In other cases I obtain the desired re- tardation in the appearance of the free poles on,cne set of cores by s. magnetic shunt, which produces a greater retardation of the current and takes up at the start a certain number of the lines set up, but becomes saturated when the current in the exciting coils reaches a predetermined strength. In the transformer the same principle of shielding is utilized. A primary conductor is surrounded \vith a line layer of laminated iron, consistin of line iron wire or plates properly insulated and interrupted. is long as the current in the prlmary conductor is so small that the iron enclosure can carry al the lines of force set up by the current, there is very little action exerted upon a. sec- ondary conductor placed in vicinity to the first; but just as soon as the iron enclosure becomes saturated, or nearly so, it loses the virtue of protecting the secondary and the inducing action of the primary practically begins. What, may I ask, has all this to do with the “old fallacy of screening ?” With certain objects in view-the enumeration of which would l. All italics are mine.-N. T.