DC trolley fires-a new solution to an old problem

Coal mine trolley fires remain a serious threat to miner safety. Over the past twenty years, nearly 70 such fires have been reported to MSHA, and of these, most were due to the inability of the circuit breaker to discriminate between a legitimate load and an illegitimate fault current. Despite the extensive research into this area in the 1970s and early 1980s, it is still a problem. The problem also persists in rail transit systems used for mass transportation. This paper reviews the problem, summarizes past work, and presents two viable techniques, one passive and one active, for discriminating between load and fault currents