This unit in the DC control system can reduce the speed of running motor to the cathead speed controlled by hand wheel. Once the foot switch is released by the driller, dynamic brake is automatically started by time delay to save the time of drilling.

In the AC variable frequency control system, the brake unit and brake resistor are automatically put into operation under the generating condition to generate dynamic brake, realize stable and adjustable running speed of winch and suspension of drilling rig, and prevent over-turn of the rotary table.