Large-capacity motors must be light-loaded, no-load start, heavy-load start, frequent start, and forward and reverse rotation start (such as electric hoist, driving, etc.). For a large-capacity motor, on the one hand, it is difficult for the power supply circuit and transformer capacity to meet the conditions for the direct start of the motor. On the other hand, the powerful starting current impacts the power grid and the motor, affecting the service life of the motor and detrimental to the stable operation of the power grid. Therefore, large-capacity motors and motors that cannot be started directly must be started with reduced voltage.

There are many vehicle-mounted dust control fog cannon fans. In order to reduce the impact of fan startup on the generator, motors above 7.5kw generally adopt the reduced voltage start method. The reduced voltage start is divided into star-delta start and frequency conversion. Start, soft start, etc. The most economical starting method is star-delta starting, but the conditions for star-delta starting: it must be a delta-connected motor, which can be as many as kilowatts, and the star-connected method cannot start.