Four methods for step-down starting of three-phase cage asynchronous motor

The methods for step-down starting of three-phase cage asynchronous motor are: stator winding string resistance (reactance) starting; -Y —△ buck start; Extended edge triangle buck start; Autotransformer step-down start. The essence of step-down starting is to reduce the voltage applied to the stator winding of the motor during start-up to reduce the starting current; After starting, the voltage is restored to the rated value, and the motor enters the normal working state.

1. Stator winding string resistance (reactance) starting control circuit

1. Stator string resistance step-down automatic start control circuit

(a) It is the automatic start control circuit for the resistance step-down of the motor stator winding string.

The working principle of the circuit is as follows: close the power switch QS, press the start button SB1, KM1 is energized and self-locked, the motor stator winding is connected to the resistance R step-down start, and at the same time, KT is energized, after the delay, the KT normally open contact is closed, the KM2 energized main contact shorts the starting resistor R, and the motor enters the normal operation of full voltage. 2. Manual automatic hybrid control circuit 2, autotransformer step-down start control circuit Autotransformer step-down start refers to the use of autotransformer to reduce the starting voltage added to the stator winding of the motor when the motor starts. After the motor starts, the autotransformer is disengaged to make the motor operate normally at full voltage. 1. Button, contactor control autotransformer step-down start control circuit three, star-delta step-down start control line star-triangle (Y-△) step-down start refers to when the motor starts, the stator winding is connected into a star, so as to reduce the starting voltage and reduce the starting current; After the motor starts, the stator winding is reconnected into a triangle to make the motor run at full voltage. Y-△ starting can only be used for motors that are △-shaped joints during normal operation. 1. Button and contactor control Y - △ buck start control circuit diagram 2.19 (a) is the button and contactor control Y - △ buck start control line. The working principle of the line is: press the start button SB1, KM1, KM2 to get power and engage, KM1 self-locking, the motor star start, when the motor speed is close to the rated speed, press SB2, KM2 to power off, KM3 to power and self-lock, the motor is converted into a triangle full voltage operation. 2. Time relay control Y - △ step-down start control circuit diagram 2.19 (b) for the time relay automatic control Y - △ step-down start control line, the working principle of the circuit is: press the start button SB1, KM1, KM2 to get the power to pick-up, the motor star start, at the same time KT is also electrified, after the delay time relay KT normally closed contact opens, so that KM2 is powered off, normally open contact is closed, so that KM3 is energized closed and self-locking, and the motor is switched from star to triangle normal operation.