Detection of downed trolley lines using arc signature analysis

"A cost effective and practical system for monitoring hauling system electrical current patterns was developed. The aim was to reduce the hazards associated with electrical fault currents from fallen coal mining trolley hauling system lines. The current could result in local heating or arcing and thus increase the risk of a fire. Computerized electrical current analysis techniques were tested at several Pennsylvania coal mining sites on mining trolley hauling systems using a range of currents. Current readings were taken during all phases of the loading process, under normal (light, intermediate and heavy traffic) and during simulated arcing and bolted fault conditions. Voltage data collected from these trials were used to develop a microprocessor based fault detection algorithm, which field tests showed was 95% accurate. The frequency of the rectifier current and the imposed fault signal were used to detect arcing faults. The authors conclude that this improves the detection and extinguishing of self sustaining arcs thus minimizing fire risk." - NIOSHTIC-2Also available via the World Wide Web.Includes bibliographical references (p. 10)

Evaluation of a signaling and warning system for underground mines

"A wireless signaling and warning system applicable to both coal and noncoal underground mines was evaluated. A TeleMagnetic Signalling Systems wireless ultra low frequency electromagnetic signaling system was installed at an experimental mine site at Lake Lynn laboratory, Pennsylvania. The system used a transmitter and antenna system which produced a low frequency electromagnetic field with a programmable carrier output frequency of about 2 to 3 kilohertz. A commercial smoke sensor was interfaced to a remote portable transmitter, and the alarm of the sensor was used to trigger the central evacuation and paging transmitter system during experimental mine fires. The underground/surface receivers flashed cap lamps and activated remote devices, such as strobe lights, within 30 to 40 seconds after the encoded signal was received. Evaluation results showed full mine coverage of the electromagnetic field and the encoded signal was received at the farthest point underground and on the surface perimeter. The cost of a signaling and warning system such as the one installed at the experimental laboratory was about 20,000 dollars." - NIOSHTIC-2Also available via the World Wide Web.Also available via the World Wide Web.Includes bibliographical references (p. 15-16)