How do star-delta step-down start, autotransformer step-down start, and soft start work respectively

       How do star-delta step-down start, autotransformer step-down start, and soft start work respectively
　　There are three common step-down start-ups: star-delta step-down start, autotransformer step-down start, soft start, and a three-phase resistor step-down start, which is not used much. There is also a side-delta decompression start, which is a start-up method evolved on the basis of the star-delta circuit, and the principle is similar to that of the star-delta circuit.
　　1. Star-delta step-down start
　　The star-delta step-down start is more common, and it is divided into manual control and automatic control. When starting, the motor is star-connected. At this time, the voltage of each winding of the three-phase motor is 220V, and the starting current is small, but it can reach a certain speed. When the voltage on each winding of the three-phase motor is 380V, it operates normally.
　　Two, autotransformer step-down start
　　When starting, the motor is connected to the autotransformer in series, the voltage is reduced and the time relay starts to work. After the set time is reached, the autotransformer is disconnected and connected to the three-phase power supply to realize full-voltage operation. The difference from the star-delta step-down start is that one is converted through two wiring connections of the motor, and the other is started through low-voltage autotransformer.
　　Three, soft start
　　The term soft start is relative to hard start. What is hard start? In layman's terms, it is direct start, and soft start is also a kind of step-down start. However, the soft start is more intelligent, and the parameters can be set according to the needs. When starting, the motor is connected to the soft starter for low-voltage start. After the start is completed, it becomes the AC contactor control of the bypass, and the power supply at the upper end of the contactor is full-voltage power supply. Compared with the first two kinds of step-down starting, the soft start is more stable, and the protection function is more comprehensive, and the cost is also the highest.