Low level fault recognition on coal mine dc trolley systems
Between the years of 1970 and 1981, 31 out of 134 reportable mine fires were caused directly or indirectly by trolley system faults. Since 1981, the author has personally investigated three fires in Consolidation Coal Company mines. All three fires were caused by trolley system faults, and two of these fires persisted for more than thirty minutes. In many electrical systems, the magnitude of the available fault current is several times that of the normal load current. This is not the case with most coal mine trolley systems, where the fault current may be as low as 125% of the normal load current. Therein lies the problem. What is needed is a way to detect low level system faults (less than 300 amperes), and trip all necessary circuit breakers, while allowing legitimate 5000 ampere trolley system loading to occur. This dissertation describes such a system based on rate of current rise and duration of the current pulse. Low level faults that previously went undetected can now be recognized, and quickly and safety deenergized; thereby significantly reducing the risk of a mine fire. It is strongly believed that the system of protection outlined in this dissertation will greatly improve the safety of any coal mine trolley system.
- Research Organization:
- Pittsburgh Univ., PA (USA)
- OSTI ID:
- 6416240
- Country of Publication:
- United States
- Language:
- English
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