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Power Trans.
The new Thomas Ince Studios at Culver City, CaHfornia, are securing excellent results from their 250 KW. threewire rotary installation. In the case of this installation, constant voltage on the 2200-volt power circuit is obtained by means of an induction regulator installed in the sub-station of the Southern California Edison Company.
2. Motor-Generator Sets. Motor-generator sets are built in several combinations with respect to the driving motor. The only type we need to consider for studio applications are those driven with alternating-current motors. In this classification we will consider sets driven by squirrel cage induction and synchronous motors.
As induction motors have generally been used, we will consider the characteristics of this type first. The induction motor has what is commonly known as "Slip." By this we mean that the motor will slow down slightly with an increase of load. As the generator is directly connected to the motor, it will correspondingly decrease in speed, resulting in a slight drooping characteristic in the generator or direct-current voltage. The speed of an induction motor is practically constant under constant load conditions, from 80 per cent, normal voltage to slight over-voltage. This characteristic is a point in its favor where a studio is located where there is slight voltage fluctuations on the incoming power line. Induction motors only should be considered in the smaller sizes ranging up to 100 KW. capacity, except in special cases. The power factor of the squirrel cage induction motor will vary from about 74 per cent, at one-quarter load to about 92 per cent, at full load. These motors are always started with auto transformers in the starting circuit so that the starting current is not excessive. Normally, the starting
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