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 cu rrent. Despite the extensive research into this area in the 1970's and early 1980's, it is still a problem. The problem also persists in rai l transit systems used for mass transportation. This paper reviews the problem, summarizes past work, and presents two viable techniques for discriminating between load and fault currents.