Three-phase asynchronous motor starting mode

1、Direct start

However, the current of three-phase asynchronous motor can reach 6-7 times of the rated current during direct starting, which is a big impact on the power grid, especially for high-power motors.

2、Frequency sensitive resistance starting

Frequency-sensitive resistance starting refers to series connection of frequency-sensitive resistor in the main circuit when the motor is starting, so as to reduce the starting current. Frequency sensitive resistance can change the starting current smoothly, the impact on the power grid is smaller, is the more ideal way to start. However, high-power frequency sensitive resistors are used in the form of inductance, so in use will produce a large electromagnetic eddy current, which will reduce the power factor of the power grid.

3、Bucking voltage starting

The main types of reduced voltage starting are thermal autocoupled reduced voltage starting and star-delta reduced voltage starting.

The main types of reduced voltage starting are thermal autocoupled reduced voltage starting and star-delta reduced voltage starting.

Star-delta buck starting refers to a method of changing the starting voltage by changing the wiring of the motor, thus reducing the starting current, which can only be applied to motors whose normal wiring method is delta connection. In starting, use the relay method to make the motor wiring for star, at this time the motor voltage per phase is reduced to one-third of the original root, the motor speed reaches about 80% of the rated speed, the control relay to change the motor wiring for delta, the motor starts to run normally. Advantage is that it can save the autotransformer, reduce costs, while the wiring method is simple, greater reliability. The disadvantage is that it is not possible to change the ratio of the starting voltage, and at the same time, it is not possible to use the motor in the star connection.