Transient processes at single phase-to-ground faults in combined grounded networks

This paper deals with the combined method of neutral grounding when a high-value resistor is continuously connected to a neutral in parallel with a Petersen coil. Monitoring of processes at single phase-to-ground faults was organized in the 6 kV network of the large-scale iron and steel plant. Within the investigation, more than 200 oscillograms of phase-to-ground voltages were analyzed. Based on recorded oscillograms, the comparison between processes at ground faults in the resonant grounded network (grounding through a Petersen coil) and in the combined grounded network (grounding through a high-value resistor in parallel with a Petersen coil) was done. Numerical values of dangerous for network insulation transient processes, frequency distributions of overvoltage levels, and arc durations were obtained by methods of statistical processing. Field experience of combined grounded networks shows that continuously operated neutral grounding resistors reduce the amount of emergency outages caused by ground faults 4-6 times and decrease undersupply of energy to customers; maximum overvoltage levels, arc duration, insulation breakdowns and multiplace faults also decrease.