Three ways to start the motor are:

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

2. Step-down starting: Step-down starting is mainly the hot auto pressure reduction start and star delta step-down start. Thermal auto-reduction start-up refers to reducing the motor voltage at start-up through the auto-transformer and reducing the starting current. It is generally reduced to about 55% to 75% of the rated voltage. The advantage is that the starting voltage can be easily changed by changing the number of taps of the self-turning transformer. The disadvantage is that it requires the use of self-turning transformers, which is costly. Star-delta step-down starting is a method to reduce the starting current by changing the starting voltage of the motor by changing the connection mode of the motor. It can only be applied to a motor whose normal connection mode is delta connection. When starting, use the relay method to make the motor connection mode star, at this time, the voltage of each phase of the motor is reduced to the original root number one third, the motor speed reaches about 80% of the rated speed, and the control relay changes the motor connection mode to Triangle, the motor starts normal operation. The advantage is that the self-turning transformer can be saved and the cost can be reduced. At the same time, the wiring method is simple and the reliability is large. The disadvantage is that it is not possible to change the ratio of the starting voltage and it is not possible to use a star-connected motor.

3. Frequency-sensitive resistance starting: The frequency-sensitive resistance starting means that the frequency-sensitive resistance is connected in series in the main circuit when the motor starts, thereby reducing the starting current. The frequency sensitive resistor can smoothly change the starting current and has less impact on the power grid. It is an ideal starting method. However, current high-frequency frequency-sensitive resistors are all in the form of inductors, so they will generate large electromagnetic eddy currents when in use, which will reduce the power factor of the power grid.

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