Reduction of Mining Electrical Hazards Through Improved Engineering Controls

Mine electrical systems are generally recognized to be safe and reliable. However, an unacceptably high incidence of injuries and fatalities still result from electrical hazards, as evidenced by the 1200 lost time injuries and 75 fatalities that occurred in the 1990's. Many of these accidents resulted in permanent impairment or serious disfigurement. In addition to these hazards, strong evidence suggests that energy from lightning strikes can, and has, caused methane ignitions in underground coal mines. The scope of work described in this proposal addresses safety hazards associated with electric arcs, and step and touch potentials that occur in coal and aggregates mining operations. Specifically, the following work is proposed: . A study of sensitive ground fault technology (SOFT), as practiced on high-voltage longwall power systems, and the possible adverse effects of distributed system capacitance on ground fault currents and transient overvoltages will be conducted. Methods for reducing electrical hazards, e.g., the application of resonant grounding, will be evaluated, and recommendations for best practices for implementing SOFT on longwall power systems will be performed. . A study of high-resistance grounding, as used in underground coal mine high-voltage distribution systems, and the possible adverse effects of distributed capacitance on ground fault currents and transient overvoltages will be conducted. Methods for reducing electrical hazards caused by ground faults, e.g., application of resonant grounding, will be evaluated, and recommendations for best practices will be performed. . A model capable of analyzing the voltages and currents in underground coal mines resulting from surface lightning strikes will be developed. Instrument packages capable of monitoring lightning events that propagate into a mine will be installed in two coal mines. . An assessment of lightning as an ignition source will be performed. .An assessment of grounding practices in the aggregates industry and the advantages and disadvantages of implementing high-resistance grounding will be performed. A set of recommended best practices for implementing high-resistance grounding in the aggregates industry will be generated, and an engineering control for converting to this type of grounding system will also be developed. .An analysis of shock hazards in the form of step and touch potentials from lightning in aggregates operations will be conducted. A set of recommended best practices for mitigating the shock hazards will be developed. PSpice software will be used to conduct the analyses of high-voltage longwall and mine distribution systems. Equipment manufacturers and mine operators will be consulted to obtain or validate equipment sizes and cable lengths for the models. Current Distribution, Electromagnetic Fields, Orounding and Soil Structure Analysis (CDEGS) software from Safe Engineering Services will be used to conduct the modeling and analysis of lightning events. The proposed research will be conducted over a three-year period by Virginia Tech as the primary contractor and the University of Kentucky as a subcontractor to Virginia Tech. The investigators have extensive backgrounds in mine electrical systems and electrical safety.