Announcement of the "Performance of the Tesla Motor" article

"El'ty," May 15, publishes a number of curves of the performance of a 50-hp motor which is running at the Westinghouse works, on the regular two-phase circuits at 220 volts, 3,000 alternations and 750 revolutions. The maximum starting torque of which the motor is capable, is a little over 2.5 times the full load running torque but this starting torque is not required in ordinary practice, as a resistance in the secondary of the motor has such a value that the starting torque is about 1.5 times the full load running torque; with this resistance the current taken by the motor at starting is about 50 per cent. more than that at full load; when running unloaded the motor takes 18 apparent horse-power; the speed falls less than 2 per cent. from no load to full load; the apparent and true efficiencies rise very rapidly as the load increases; at one quarter load the former is 57 per cent. and the latter 84 and at full load they are 81.5 and 89.5, respectively; the latter is said to be better than that ordinarily attained by direct current machines of the same output, and the light load efficiency is much better; the all-day efficiency will therefore be higher than that of a direct current motor if the power required is variable; the ease with which it can be controlled both "as to speed" and as to direction of rotation make it superior to the ordinary motor.