A New Tesla Alternating Motor

Friday, April 25, 1890
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910 THE ELECTRICAL ENGINEER.. [Ap.a1¢>,1soo. principle, among them one having a. number of fields, which is particularly adapted to a rate of albernations corresponding to those now in general use on alternating hirouits.

APnl9»1890] THE ELECTRICAL ENGINEER. 209 A NEW TESLA ALTERNATING MOTOR. OUR. readers are already acquainted with the Tesla alter- nating current motor, which has now gone into practical application, and the operation of one type of which is based upon the fact that when an alternating current is passed through the coils of such a motor, the field magnets or poles do not appear to manifest their attractive effect upon the armature simultaneously, the magnetic attraction of some appearing to lag behind that of others, with the result of producing a torque and rotation of the motor. Mr. Tesla has, however, developed another form of these so-called “ magnetic lag ” motors, but in operation it differs from those just described, in that the attractive effects or phases of the poles, while lagging behind the phases of current which produce them, are manifested simultaneously and not successively. The manner in which this is carried out, is shown in the accompanying illustrations, Figs. 1 and 2, which represent respectively an elevation and side view of the motor. As will be seen, the motor has two laminated magnetic pole-pieces cc’ of soft iron or steel. The laminated disc- ml J Zl -MH `l‘l`ll/'./, W é » ‘ ~\.'\f‘u; il‘

nm nrrmnsnuo :ovaim mn » APB” 17' F8913 ‘ELECTRICAL REVIEW. 487 deeper it. Thesecond wave, of ` opposite direction, was not strong enough to rerersethe magnetism produced by the first wave, and only weakened itxsomewhat ; but because. of its longer duration it entered dee r into the steel and mag- netised thslayer undemeath in tif; opposite direction to the surface, so that by “grinding off the surface layer the magnetic moment of the r reversed ; and if the rwistance of -the electric circuit was low enough to allow a third wave to be produced with perceptible intensity, undemeath the second ayer a third one was found, magnetised in the some direction as the surface. This phenomenon shows that even such veriy rapid oscillations produce magnetism. _ _ , was very much interested in reading the arguments which Prof. Thomson proffered for the existence of carbon vapour in the electric arc, and I must consider the arguments as very strong. The only fact which seems to me not quite in agree- ment with the existence of carbon vapour, is the spectrum of the electric arc. The copper arc, the iron arc, show the characteristic spectra of those metals, with their many lines. The carbon arc, if containing carbon vapour, ought to"show the-until 'now unknown-carbon spectrum.- But nothing of that kind ; it gives an entirely continuous spectmm, quite similar to the spectrum of glowing solids. ~ This fact,-I believe, needs still a satisfactory explanation, and I should like to hear how Prof. Thomson ex lains the absence of a characteristic carbon spectrum in tllie electric are. I should like to hcar, also, whether any experiments have been made to determine the exact temperature of tho are and the glowing carbons. The only temperature determinations of which I know are already of rather old date and made by an ~Italian, Rcsetti, which measured the heat radiation by means of a themropile and found the temperature of the tip of the positive carbon to 3,900° G., the tip of the negative carbon to 3,l50° C., but the temperature of the flame higher -4,800 to 4,8-t4° C. These figures do not agreo with the data given by Prof. Thomson, who considers the positive carbon as the hottwt part of the circuit. Itosetti used cur~ rents from 8 to 6 ampéres. _ The explanation of the instability of the electric alter- nating arc, because of the alternating cooling off of the carbons during the zero period of the current is certainly the nearest one, and, therefore, generally accepted. But whether it agrees with- the real proceedings must still be doubted. Theoretically, at least, these fluctuations of temperature should be expected to be so small that they could ave no influence on the conductivity of the arc. . An experiment to determine the fluctuations of temperature of an electric conductor, caused by .the alternations of the current, was made on a piece of co per wire, one millimetre thick and 657 centimetres long. I current of - 6'4 ampérm was sent through with only‘5,840 alternations per minute, and the lengthening of the wire measured. The increase of temperature was 37° C.; but the maximum variation of temperature calculated to only ‘019 degree O., that is, one-twentieth per cent. of the whole rise of temperature. (“ Das Gesetz zwischen Ausdehnung und Strcmstiirke fiir einen von galvanischen Wechselstromen. , durchiiassenen Leiter,” von Dr. Cranz; Zeitschrift fiir Matbematik und Physik, Dresden, 1889, p. 92.) ' Although this calculation is not nite conclusive for the somewhat different conditions in the éectric arc, it is sutlieient for making the assumpfion of so great and rapid cooling down of the arc during t e time zero current doubtful. ' ‘ ‘ » ` But if we consider the energy consumption .of the are as caused by a counter E.M.F., a ind of polarisation, and at the hand of the facts must assume that this counter E.M.F. of the arc in very wide limits is nearly independent of the cur- rent strengtb, then the apparentresistanoe of the arc must vary inversely as the current intensity, and in consequence of this, in an ordinary altemating aro light circuit, the height of the current wave must be increased at its crest, decreased near its minimum position, so that the time of minimum current is greatly increased, and the shade of- the wave becomes more triangular. 1 . _ But if the altemator ,is so well self-regulating that the cu.rrent'wave, in spite of the varying resistance, is kept sinusoidal, that is, regulating in timeso short that it is'smull even in comparison with the wave length of the alternating current, as is the case in the Stanley-Westinghouse constant cunent altemator, then the alternating arc shouldrbecome just as steady as the continuous current arc. Now, in Mr. Tesla's high frequency machine this condition was certainly fulfilled, its sclf-induction being very large, as .the tendency of yielding constant current shows, and self-indut:tion regu- lated the impressed E.M.F., according to the sine wave of the curnen%>roducing the rectangular shape of the \V1`lV€_0£ imperessed .M.F., as Bil0\Vll in the curves given by Mnssrs. To y and Walbridge, for the Stun|ey~Westinghouse alter- rérptor, in ttéeir pnpcr read before the American Institute of ectrical nginecrs. This particular shape of E.M.F. and current might hn\'e_a great deal to do with the stcadiness nnd nnstcndiness of the arc. _ Therefore, it would be of ver; great intcrest,`in'thc same way as it has been done in ornell Universit with thc Stanle -Westin house alternator, to determine the shape of the E.hI.F. auf the current wave for an altematcr of very low self-induction, for instance, with n disc urmaturc, run- ning am light. Then I should expect to find thc opposite phenomenon; the impressed E.M_ . retaining its sinusoidal omi, and the current wave assuming n more triangular, shape, at the same time causing unstendiness of tho arc. Yonkers, N.Y., dl/:rch Qtilh, 1801.