When the AC asynchronous motor starts under the rated voltage, the initial starting current is very large, which often exceeds many times of the rated current (generally 5 ~ 7 times). In order to reduce the starting current and do not affect the power grid, the AC asynchronous motor is usually started by reducing the voltage. The common step-down method is to use reactor or self coupling transformer, The starting process of AC motor is very short (usually a few seconds to two minutes). After starting, the reactor or auto coupling transformer for step-down starting will be cut off. The product is designed according to the starting characteristics of high-voltage asynchronous motor, and the matching motor power is 220 ~ 1400kW.