The thyratron motor at the Logan plant

The motor is rated 400 hp, 2,300 volts, 3-phase, 60-cycles, 40°C and was designed to drive an induced draft fan having a speed range from 625-350 rpm. It closely resembles a standard synchronous motor with a rotating field, except that it has two independent star-connected stator windings installed in the same slots. Unlike a synchronous motor, however, the field terminals, after being brought out through slip rings, connect to the neutral points of the star windings. The six remaining power leads connect in a special arrangement to a series of 18 type FG-118 thyratron tubes, each having a continuous rating of 12.5A and a maximum rating of 75A. During the year the motor has been in operation at this writing, a comparatively large number of minor difficulties arose. Yet in spite ??of these, the plant operators are very enthusiastic about its performance. Experience has shown them that no drive compares with it for ease of control, for smoothness of draft regulation, for ability to rotate at very low speed, and for almost entire elimination of fan blade maintenance expense. In view of the fact that plant operators are pretty hard-headed and tend to look with suspicion on new "gadgets," this response would seem convincing evidence of its success from a practical standpoint.