E-Mail: sales@expertengineers.co.in
Phone: (+91)9971870008, (+91)9711609607
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Auto transformer Starter

Power and Motor Control Center

Auto Transformer Starters are most popular electromechanical reduced voltage starting devices providing maximum starting torque and minimum starting current for large induction motors where availability of starting current islimited but a minimal starting torque is require.  An induction motors draws 6 to 10 times of full load current while accelerating to full speed if directly connected to power supply.  With auto transformer startersthe reduced voltage applied to the motors results in lower current and high torque.


Voltage 50% Voltage 65% Voltage 80% Voltage
Torque 25% 42% 64%
Line Current 25% 42% 64%
Motor Current 50% 65% 64%

The auto transformer starters manufactured by us are comprise of run contactor, start contactor, star contactor, motor protection relay for protection against overload, single phase, reverse phase, phase imbalance, earth fault, lock rotor current, under/over voltage etc, auto transformer, timer and other accessories.To start the motor, first the star contactor is engaged followed by start contactor supplying reduced voltage through auto transformer limiting input current to stationary motor while accelerating. The motor continues to accelerate and after preset time of 8 to 12 seconds the star contactor is opened and momentarily even lower current is supplied by auto transformer winding acting like inductors connected in series with motor. The time is short, just enough to disconnect star contactor and engage run contactor to supply full voltage to the motor to accelerate to achievefull speed. At this point motor can work on full load and transformer no more required disengaged by opening start contactor.