High power three phase asynchronous motor can not start directly in general, and need to start with starter.
The starter is divided into manual and automatic two types according to operation mode. The star triangle starter is commonly used in the manual starter of the AC motor, which belongs to the way of starting the step-down. When starting, the winding of the AC three-phase motor is connected to the starlike shape, so that the applied voltage of each phase is reduced to phase voltage, so as to reduce the impact of the starting current.
Starting mode of three phase asynchronous motor
1, direct starting. However, the current can reach 6-7 times of the rated current when the three-phase asynchronous motor starts directly. It has a great impact on the power grid, especially the large power motor.
2, the step-down starting. The starting of the hypotensive starting and the step-down starter of the star triangle are mainly caused by the step-down starting.
The start of the hot self - Lotus depressurization is to reduce the voltage of the motor and reduce the starting current by the self - coupling transformer starting. It is generally reduced to about 55%-75% of the rated voltage. The advantage is that the starting voltage can be easily changed by changing the number of the tap ring of the self - coupling transformer. The disadvantage is the need to use the self - coupling transformer, the cost is larger.
The star delta start is a way to change the starting voltage by changing the wiring mode of the motor, so as to reduce the starting current. It can only be applied to the normal connection mode of the motor connected by triangle. At the start, the use of relay method makes the motor connection mode for each star, the motor phase voltage decreases to the square root of 1/3, left and right motor speed to the rated speed of the motor control relay 80%, change the connection mode for the triangle, the normal operation of motor start. The advantage is that it can save the self - Lotus transformer and reduce the cost. At the same time, the connection method is simple and the reliability is great. The disadvantage is that the ratio of the starting voltage can not be changed, and the motor that is connected to the star can not be used at the same time.
3, frequency sensitive resistance starting. The starting of frequency sensitive resistance refers to the series of frequency sensitive resistors in the main road when the motor starts, which reduces the starting current. The frequency sensitive resistor can change the starting current smoothly and have less impact on the power grid. It is an ideal starting method. But the high-power frequency sensitive resistance is the form of inductor, so when used, it will produce large electromagnetic eddy current, which will reduce the power factor of the power grid.