Arrangement for braking a three-phase motor driven hoist

Claim 1

In a combined driving and braking system for a hoist, the combination comprising a polyphase driving motor and the rotor of which is coupled to the hoist for driving the latter at a speed determined by the number of poles on the motor, circuit means including a first switch for selectively connecting the stator of said drive motor to a polyphase power supply source, a polyphase eddy-current braking machine having a stator with at least three times the number of poles as are provided on said drive motor and a solid rotor provided with radial longitudinal slits and copper ring discs soldered onto the opposite ends of said rotor, said rotor of said eddy-current braking machine being coupled to said hoist for braking the latter, circuit means including a second switch for selectively connecting the stator of said eddy-current machine to said polyphase power supply source, said second switch being closed when said first switch is opened thereby to disconnect said polyphase driving motor and brake the hoist dynamically to a first lower speed determined by the number of poles of said eddy-current machine, a direct current power supply source, and circuit means including a third switch for connecting the stator of said eddy-current machine to said direct current power supply source when said second switch is opened thereby to disconnect said eddy-current machine from said polyphase power supply source and dynamically effect a further reduction in speed of the hoist to near stand-still condition.