Polyphase Patent Litigation

It has often been asked, Why has the transmission of power by polyphase currents made so little progress in this country, in comparison with its use on the Continent and in America? This difference cannot be wholly attributed to ignorance on the part of British manufacturing firms, nor even to a natural conservatism tinged with the feeling that the advantages of polyphase motors have been somewhat, overstated. The cause of the delay in this country has, we think, to a large extent been due to the uncertainty that exists as to what claims would be made by the owners of certain patents, and as to the ground that they considered covered by those patents. British firms have hardly yet sufficiently recovered from the costs and expenses incurred in litigation over compound winding, over incandescent lamps, and over telephones, to wish again to embark without due consideration on the troubled waters of the law. Nor is that feeling unjustified in view of the position which affairs have now assumed in America. The Westinghouse Electric Company, which controls the patents and inventions of Nikola Tesla, have instituted suits against the General Electric Company of America, and against the Stanley Manufacturing Company, for alleged infringements of Tesla's patents, claiming, as their advertisements state, that these patents cover broadly any system of polyphase alternate current distribution of power. It is interesting to note, as showing how broad is the ground claimed, that neither in the "monocyclic" system of the General Electric Company, nor in the two-phase system of the Stanley Manufacturing Company, are the motors simple rotary field motors, but modifications which have the appearance of being expressly designed to avoid any claim on behalf of the owners of Tesla's patents. The results of these actions will be regarded with interest in Europe, as it is only to be supposed that if successful in America a similar line is likely to be taken in this country and elsewhere where Tesla's patents are in force. That this question is not lightly regarded by the owners of the Tesla patents is evident from the fact, that the valuation of the Tesla patents is said to have been the point at which the recently negotiated "combine," as to patents, between the General Electric Company and the Westinghouse Company, came to a deadlock.

The ground on which the priority of Tesla's patents is likely to be contested, is probably the, till recently, forgotten rotary field motor of Baily (1879), and the motors of Ferraris; but these do not appear to entirely touch the issue. In the first of these the rotary field was produced by commutating a continuous current; in the second, by splitting a single-phase alternating current into two phases by proper arrangements of self-induction or condensers. This is a different thing from the reproduction in a motor of a rotating magnetic field, the image or reflection if the term may be used, of an existing rotating magnetic field, produced in a dynamo with multiple coils, connected to similar coils in the motor. This is the kernel of Tesla's inventions, and it remains to be seen whether his patents of 1888 will withstand the fire to which they will now be exposed. The Westinghouse Company, in any case, can claim little credit for the practical introduction of polyphase motors, for whilst the patents date back to 1888, for some years after this no definite information as to the results that had been obtained by their use was forthcoming, whilst even as late as 1891, the current lists of the Westinghouse Company, only described and showed their use, like Ferraris' motors, on single phase transmission plants for starting up synchronous motors. The credit of showing what it is possible to effect with polyphase transmission will always be connected with the names of C. E. L. Brown and Dolivo Dobrowolski. It is to be hoped, in the interests of all parties, that this question will be settled shortly and decisively, as until its conclusion a cloud will necessarily hang over a system which, in many cases, may prove of considerable value.

Meanwhile it is interesting to note what is the real position now to be assigned to polyphase power transmission and distribution, in what respects it is superior to continuous current systems, in what respects it is inferior. The answer in general terms is this, where the transmission or distribution is satisfied by motors running at a constant speed, and not requiring a turning moment greater than, say, 50 per cent. above the full load running moment, no system can beat the polyphase, either in economy in first outlay, simplicity of working or efficiency. But where variations of speed are required, or a largely increased turning moment is necessary, either at starting or when running, polyphase plant is not applicable. Great loss of efficiency always occurs when a polyphase motor revolves at a speed differing considerably from the speed of the revolving field, and the turning moment appears at any speed to have a maximum beyond which a reduction of speed decreases instead of increasing it, thus producing instability. These generalisations omit the consideration of the possibility of using higher pressures owing to the power of transforming alternating currents with simple apparatus. It may, therefore, be taken that with polyphase motors as at present made, they will be used for transmission of power in manufacturing, but for mining, for traction, for lifts, and analogous purposes, continuous current machinery may be expected to hold its own.