In this method, a solid state starter consisting of power SCR’s controlled by logic circuits is used to chop the sine-wave system power so that only a portion of the wave is applied to the motor. The logic circuits can be programmed to respond to any of several sensors to control the voltage: internal time ramp; current sensor feedback, or tachometer feedback.

In addition, most such starters also have provisions for reducing the voltage when the loading on the motor is low, thus minimizing the no load losses of the motor.

Solid State Reduced Voltage Starting

Starting Characteristics:

1. Motor terminal voltage is reduced from line voltage.
2. Motor current equals line current.
3. Starting torque is reduced by the square of the terminal voltage.

Applications:

1. Available through 4160 volts.
2. Where rate of acceleration needs to be controlled.
3. Where current limit exists, but load torque is high.
4. Where the motor runs at no-load for significant periods.
5. Where soft start (gradual taking up of slack) is desired.