Solid-State Control-Low Voltage Heating of Motors

In recent years, industrial plants have been utilizing more electric motors as drivers because of their high efficiency and reliability and lower maintenance costs. Electrified continuous process plants are using electric motors for both primary and standby drives. When these standby motors are not operating during normal plant runs, their windings collect moisture. Moisture attacks insulation and causes insulation failure. A breakdown of motor insulation may occur when a standby motor is suddenly energized to take the place of the primary motor. When it is not in operation, directly heating the motor winding with a low voltage system, coupled with automatic control, will guard the motor from moisture attack and extend its service life. The experience with low voltage heating of motor windings as described by M. H. Yuen in his article [1] has proved its effectiveness. However, conventional relays, timers, contactors, etc., were utilized in the circuits.