Several starting methods for high-voltage motors:

1. When an ordinary squirrel cage motor is started directly at no load and full voltage, the starting current will reach 4-7 times the rated current. When the motor capacity is relatively large, the starting current will cause the grid voltage to drop sharply, and the voltage frequency will also change, which will disrupt the normal operation of other equipment on the grid, and even cause the grid to lose stability and cause greater accidents.

2. The large current when the motor starts at full voltage will produce a great impact on the stator coil and the rotor squirrel cage bar, which will damage the winding insulation and cause the squirrel cage bar to break, causing the motor to malfunction. The large current will also generate a lot of Joule heat. , Damage the winding insulation and reduce the life of the motor.

3. The start of the series reactor is a step-down voltage start. When the full voltage is switched, the torque has a jump, which will cause mechanical shock. Compared with direct full-voltage start, the probability of operating over-voltage is smaller. However, due to the random nature of high-frequency oscillations, large-scale operating overvoltages may still occur.

4. Compared with the reactor step-down start, the auto-transformer step-down start has a smaller starting current when the same starting torque is obtained, which is suitable for the situation where the resistance torque is relatively large.

5. Use a medium-voltage inverter as a soft-start device to start the motor. Its starting performance is very good, but the medium-voltage inverter is expensive. In addition, because the inverter technology is still in the development period, its reliability is not very high. The user's maintenance technology Can't keep up, this is the reason why this method is not widely used, and it is generally used on imported equipment. Using a frequency converter to start the motor can achieve no operating overvoltage, but the output voltage of the frequency converter contains a large number of higher harmonics, which will also cause damage to the motor.

6. The medium-voltage motor soft-start device adopting thyristor series technology has high requirements for the consistency of the component characteristics, the screening rate of the components is very low, and the price of the screening instrument is very high, which makes the device more expensive high. In addition, after a period of use, the parameters of the components will also change, which will reduce the voltage equalization performance of the components, which can easily cause damage to the entire string of components and reduce the reliability of this device.

7. Water resistance and liquid variable resistance soft start device. The water resistance type relies on the movement of the plate and the large current to vaporize the water (the surface of the plate) to form a high resistance to change the resistance of the liquid to control the starting current (voltage). The variable resistance is controlled by the amount of impurities, the size of the plate and the high resistance generated by the large current that vaporizes the water near the plate.

8. The switching transformer type medium voltage motor soft starter uses a switching transformer to isolate high voltage and low voltage. The low voltage winding of the switching transformer is connected with the thyristor and the control system, and the voltage on the high voltage winding is changed by changing the voltage on the low voltage winding. , So as to achieve the purpose of changing the terminal voltage of the motor to realize the soft start of the motor. During the start-up process, the switching transformer is always in two working states of on and off, and the loss of the switching transformer is small.