An Identification Method for Ground Potential of Grounding Grid in Urban Substations Considering Metro Stray Current

Different dc interference sources cause variations in ground potential distribution and have an effect on the choices of corrosion inhibition strategies. Therefore, accurate identification of the sources is of great significance. In the urban substation field test, we found such novel phenomena as large fluctuation, frequent polarity reversals, and extended duration in the grounding grid to soil potential (GGSP), as opposed to those of high-voltage direct current (HVDC) grounding electrode current and geomagnetically induced current (GIC). However, considering that the GGSP induced by GIC is random, it is difficult to directly determine its dc interference source. To investigate the phenomena, we employed a mathematical derivation and ground potential coupling simulation model, revealing that the metro stray current is the root cause of the GGSP fluctuation. Furthermore, the effect of metro operating status and departure intervals on the amplitude and frequency characteristics of the GGSP was analyzed. By utilizing the zero crossing count (ZCC) and offset potential indicators, an identification method for the ground potential of the grounding grid in urban substations considering metro stray current was proposed. Using field test data, this method has been validated with respect to accurately identifying metro stray current, HVDC grounding electrode current, and GIC. This validation provides a basis for assessing and suppressing grounding grid corrosion caused by dc sources in practical engineering.