An oscilloscope method for eliminating the interference and disturbance voltages for the earthing measurements of large earthing systems in substations

This article describes an oscilloscope method for eliminating the interference and disturbance voltages for the earthing measurements of large, extended or interconnected earthing systems in substations where the impedance to earth is very low (|ZE| < 0.3 Ω). The presented oscilloscope method is based on a heavy-current injected method at network frequency. Two ways of obtaining the final result from oscilloscope measurements are described and presented with practical examples. The accuracy of this method using an oscilloscope was confirmed by a comparison with results obtained using conventional methods for practical cases of touch-voltage measurements, i.e., the beat method and the polarity-reversal method. These comparative measurements were made in three substations. The article also describes the advantages of this method.