A Wide Application of the Tesla Polyphase Patents

A WIDE APPLICATION OF THE TESLA POLYPHASE patents was made by Judge Seaman in the Federal Circuit Court at Milwaukee, Wis., in the decision in a suit brought by the Westinghouse Electric & Mfg. Co., of Pittsburg, Pa., against the National Electric Co., of Milwaukee, Wis. The complainants, owners of the Tesla polyphase patents, sought to enjoin the defendant from the further sale of synchronous motors (reversed alternating-current generators). Their contention was that the claim of Tesla for producing a rotating field by means of currents differing in phase applies to synchronous polyphase motors and rotary converters as well as to induction motors. This contention was upheld by the court. The material portion of the decision delivered Feb. 24, 1905, is reproduced in the “Electrical Review” of March 4, from which we quote the following:

Whether the effect of the Tesla invention in its production of the “whirling field of magnetic force” is identical with that of a rotating physical magnet, as argued by experts and counsel, does not impress me as material to this issue. Nor does it seem material that in the one form of motor “the rotation is produced by the unaided effect of alternating out-of-phase currents,” as described by counsel, and that so applied a self-starting motor is obtained. The discovery was of means and method in the polyphase rotating field motor to produce the whirling field of force, and employment thereof was patentable with or without direct-current excitation of the armature or secondary element. So the fact that its use produced a self-starting motor without the aid of such excitation cannot alone serve to limit the invention to that effect, and I find no such limitation in the terms of the patent. The quotations from the arguments of counsel and experts for the complainant in prior cases, urging the distinction of this self-starting effect in reference to the application of the generic patents to non-synchronous motors, are without force in the present controversy, and it is unnecessary to ascertain their consistency or inconsistency with the interpretation sought on this hearing. Unless limitation to self-starting motors arises out of the prior art none can be imposed upon the claims in suit.

The further propositions urged by way of defence — aside from the defence founded upon prior inventions of the synchronous type to be considered — are these (1) that the synchronous motor of the defendant is the old generator of the art, simply reversed; and (2) that the Tesla invention is not present therein, because (as asserted) “the prepondering magnetization of the” direct current displaces and obliterates the “shifting alternating-current magnetization,” or Tesla “whirling field of force.” However specious both propositions appear on their face and in the argument, neither of them impresses me as controlling.

I believe that no proposition in the able and extended arguments on the part of the defence have been overlooked in my consideration of this case, although it has not seemed needful to discuss all of them for the purpose of this opinion. My conclusions are that the defendant’s synchronous motor structure and operation are within the generic invention as patented, and expressly covered by the claims of Nos. 381,969 and 382,281; that the invention is utilized in the defendant’s motor operation, notwithstanding the introduction of direct-current excitation to make it synchronous, in lieu of the full realization of the revolving field effect for self-starting; that such supplemental aid does not escape infringement, with or without advantage in such associations; and that, in any view the combination patents referred to are not limited to after-effect of the direct-current excitation, but apply to the defendant’s combination. Decree will be entered accordingly as prayed in the bill.