Application of dynamic braking to mine hoisting systems

Accidents occurred on counterweighted mine hoisting systems when the mechanical brake failed while the cage was empty. This allowed the counterweight to fall to the bottom of the shaft, causing the cage to overspeed and crash into the headframe. Direct-current hoist motors have the potential for preventing this type of accident by incorporating a passive electrical braking system known as dynamic braking. Installation of dynamic braking requires minimal control system modifications and modest expense. The various circuit designs that can be configured to implement dynamic braking on a DC mine hoisting system are discussed. Selection of the load resistance for the desired dynamic braking system performance is addressed. Data from tests of a mine hoisting system that was modified in the field to incorporate dynamic braking are analyzed, to provide technical credibility to the dynamic braking concept