11 May

Match with compensating key

The compensating switch can be used for starter motors with load where the star-delta switch is improper. With it, we can decrease the starting current, avoiding overload in the mains, leaving the motor with a torque sufficient for starting and acceleration. The voltage at the compensating switch is amortized by means of a three-phase autotransformer which generally has taps of 50%, 65% and 80% of the nominal voltage. We make the transition to the permanent regime by disconnecting the autotransformer from the circuit and directly connecting the three-phase motor to the mains by means of the contactor.

This procedure is done in the control dc motor 113019.00 diagram with the aid of the time relay, in which the time adjustment is made to ensure acceleration of the motor up to approximately 80% of its rated speed. Notice that at the moment of switching, the time relay switches off only coil C1, the coil C3 being energized for a short time, thus keeping the motor under voltage by means of the windings of each column of the autotransformer. This causes the current peak to be shortened at the time of switching (insertion of coil C2) because the motor is not switched off.