Tuesday, April 28, 2009

Autotransformer starter

The autotransformer starter is an electromechanical means of reduced voltage starting an induction motor. Usually, there are three sets of output taps allowing connection on the 50% start voltage, 66% start voltage and 80% start voltage. The starter operates by connecting the motor to the reduced voltage tap for a period of time and then switching to full voltage. If there is sufficient torque to accelerate the motor to full speed at the reduced starting voltage, and the start timer is set long enough, there will be a useful reduction in starting current and starting torque. If the torque available at the reduced voltage is insufficient to accelerate the driven load to full speed, the starter will change to full voltage at less than full speed, resulting in a high start current and little or no advantage over DOL starting.




Where insufficient torque is available to accelerate the load to full speed, the starter can be set to a higher tap, increasing the start torque developed.

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