It is possible to achieve soft start, and a wound motor soft starter can be used. High-power motors generally use soft start. If a high-power motor is started directly, the starting current is relatively large, and problems may occur (such as insurance systems, transmission lines, motor coils, etc.). The soft start device is: when the motor starts, the contactor will The motor connection method is changed to y connection. After the motor is initially started, it is changed to △ connection through the contactor. The principle is: when the motor is connected to y, each group of coils will withstand 1/1.732 times the voltage of the transmission voltage (that is, the reciprocal of the square root of 3) , when the motor is △, each group of coils directly bears the transmission voltage, thus achieving a soft start.
The soft start of the motor mainly adopts the following methods:
1. Reduce the power supply voltage to start
2. Reduce the power frequency to start
3. Reduce the excitation current to start
The soft starter mainly uses thyristor phase shifting to reduce the motor voltage and realize soft start.
The so-called soft start of the motor is essentially that the motor starts slowly at a lower current, so that the impact on the power grid is small, and the load margin of the transformer and control circuit can be reduced at the same time, and the service life of the equipment can be improved at the same time. Generally, when the AC motor is directly started, the starting current is 6~10 times of the test running current, but after using the soft start technology, the starting current is reduced to 1~3 times.
