Editorial Comment - The Tesla Motor and the Polyphase System

The types of alternating-current apparatus which and the Polyare in use to-day have resulted from a process phase System of evolution which has been going on for many years and in which the polyphase induction motor has been the fundamental element. The announcement of the polyphase induction motor and of the polyphase system were made by Mr. Tesla in 1888. The motor excited much interest and expectation. The polyphase system received little consideration. The motor, however, was helpless without a supply of suitable current. The alternators of that day were single-phase, they gave 120 to 133 cycles; alternators and transformers were ill adapted for supplying out-of-phase current. Persistent work, not only in the design and development of the motor but in that of the system as well was required before commercial success could be secured. In reaching this point it was not only necessary to overcome preconceived ideas of the public, but the electrical workers themselves had to unlearn, or at least readjust much of the information which they had acquired in connection with direct-current and single-phase alternating current apparatus and practice. In point of fact the Tesla invention was not merely a motor, but a system. Commercial men and engineers who did not understand the problems involved were naturally impatient and critical because the Tesla motor was not immediately supplied for operation upon existing circuits and in connection with the then prevalent types of generators. As a matter of history it is the Tesla principle and the Tesla system which have been the directing factors in modern electrical engineering practice. Alternators are now polyphase; they are of low frequency, they have close inherent regulation. All of the long distance systems for power transmission involving hundreds of installations, hundreds of thousands of horse-power and many millions of dollars of capital use the polyphase system. Nearly all of the great central stations for city railway and lighting service, even when the consumption circuits are supplied with direct current employ low frequency polyphase alternators. There is scarcely an important city or town in the country that has not a polyphase plant and polyphase apparatus is largely used for power distribution in industrial establishments.

This evolution has involved far more than the mere perfection of the motor. In fact polyphase motors as made prior to 1890 if operated in connection with modern generators would probably be more successful than the motors of to-day if operated in connection with polyphase alternators of the types first employed. The early polyphase alternators were small, they were of high frequency, they were of poor regulating qualities. Changes have been made in alternators and in transformers. Parallel operation of alternators has become a necessity, imposing exacting problems in the design and operation of steam engines. The extent to which everything in modern electrical power work has been affected by Tesla inventions makes it apparent that the polyphase motor which he proposed was no simple and isolated thing, but it was the central factor in a great and comprehensive system. The whole trend and evolution for the past sixteen years has been in the development of the polyphase system primarily that it may operate the polyphase induction motor. The realization of the Tesla invention was looked for simply in a motor to be forthcoming in a few months; it has come in an evolution of engineering practice which has been the work of years.

CHAS. F. SCOTT.