1. Direct start. However, when the three-phase asynchronous motor starts directly, the current can reach 6-7 times of the rated current, which has a great impact on the power grid, especially the high-power motor.

　　2 frequency sensitive resistance starting. Frequency sensitive resistance starting means that when the motor starts, the frequency sensitive resistance is series in the main circuit, thus reducing the starting current. Frequency sensitive resistance can change the starting current smoothly and has little impact on the power grid. However, at present, the high-power frequency sensitive resistance is in the form of inductance, so large electromagnetic vortices will be generated when used, which will reduce the power factor of the power grid.

　　3. Anti-voltage starting. The buck start is mainly from the hot lotus root buck start and star delta buck start. The thermal self-coupling step-down starting is to reduce the motor voltage and the starting current through the self-coupling transformer. Generally reduced to about 55%-75% of rated voltage. The advantage is that the starting voltage can be easily changed by changing the number of tap turns of the transformer. The disadvantage is that the transformer needs to be used from lotus root, which is costly. Star delta step-down starting refers to a method that changes the starting voltage by changing the wiring mode of the motor, thus reducing the starting current. It can only be applied to the motor whose normal connection mode is triangular connection. At this point, the voltage of each phase of the motor is reduced to the original square root of one third, the motor speed reaches about 80% of the rated speed, the control relay changes the motor connection mode to triangle, and the motor starts to run normally. The advantage is that it can save the transformer and reduce the cost. The disadvantage is that the ratio of starting voltage cannot be changed and the motor cannot be used in star connection.