Uses the winding asynchronous motor, with the rotor resistance speed, speed segment switching with AC contact-or， therefore, the discontinuity of speed adjustment, Running mechanical vibration, braking insecurity.

Start and shift impact current is big, the start current is generally 1.7 times the rated current.

At the time of speed regulation, a lot of power consumption on the slip resistance, waste is serious.

Due to the ac contact-or is frequent movementduring operation, easy to cause contact and coil burning.

Easy to speed continuously, can segment to give, continuous adjustment.

Implements the low-frequency low-voltage soft start, soft stop, make run more smoothly, small mechanical shock.

Small start-up and accelerate the process of impact current, accelerate the process of maximum starting current is not more than 1.3 times. Hoist under overload from low speed smoothly to the high speed, no large current, greatly reducing the impact to the grid.

Dump for speed of ac contact-or, time relay, etc., to improve the reliability of the system, and the operator working environment improved.

Energy saving effect is remarkable. According to the measured period of energy-saving significantly at low speed, generally can reach 30%, and the more shallow coal mine, the longer period of running at low speed, the more obvious energy saving effect.