| Underground coal mine distribution systems are composed of shielded cables which have significantly higher capacitance than unshielded cables. Also, coal mine distribution systems are required to use high-resistance grounding. As distribution systems become more extensive, the flow of charging currents due to high system capacitance can cause problems such as ground fault current significantly exceeding the neutral grounding resistor (NGR) current limit, loss of relay selectivity, and transient overvoltages in certain fault situations.; A Spice simulation model of a complete mine distribution system was developed after verification of the modeling technique to investigate the deficiencies of high-resistance grounding as currently practiced by many underground coal mine operators. In ground fault simulations conducted for high-resistance grounding, the problems of fault current significantly exceeding the NGR current, loss of relay selectivity, and transient overvoltages for resonant fault conditions described above were observed. Next, the mine distribution system simulation model was used to investigate the effectiveness of other types of grounding in mitigating or eliminating these problems. It was observed that a grounding system with a Petersen coil connected in parallel with the NGR is the most effective in mitigating the problems associated with high distributed capacitance in mine distribution systems. The combination is found to be able to control the level of fault current, maintain control of overvoltages, and selectively isolate the ground fault.; Research was also performed to calculate the voltage drop in the ground circuit under different ground fault conditions. A controlled source model of an unloaded power system was constructed and simulation results for voltage drops were found to be nearly equal to the corresponding standard inductance circuit model simulation results, thus verifying the modeling approach. Subsequently, the controlled source model was used to calculate voltage drop in the ground circuit of a loaded power system for various ground fault conditions.; Keywords: High-Resistance and Resonant Grounding, Distributed System Capacitance, Ground Faults, Ground Fault Relaying, Ground Circuit Voltage Drop. |
