Analysis and improvement of methods for calculating the resistance of substation earthing equipment

In this study, we analyze the results of calculating the resistance of substation earthing equipment taking operational factors into account. The resistance of a substation earthing system was estimated using both calculation (methods of equipment operating factors, generalized parameters and induced potentials) and instrumental (ammeter-voltmeter) methods. During operation, the resistance of the studied earthing system was found to increase in comparison with the rated values, thus reducing its overall efficiency. The resistance of substation earthing equipment measured experimentally by the ammeter-voltmeter method showed the relative error of the considered calculation methods to reach 48, 46.7 and 28.6%, respectively. With the purpose of increasing the calculation accuracy of earthing equipment resistance by the method of induced potentials, it was proposed to use an operating factor. Thus, during the substation operation period of 10, 10–20 and over 20 years, the resistance of the earthing system increases by 1.02–1.1 times due to corrosion. It was shown that the installation procedure and maintenance checks (conducted at least every six years) increase the resistance of earthing systems by 1.02 and 1.05 times, respectively. Lightning discharges and short-circuit currents affect the corrosion rate of earthing systems, thereby increasing their resistance by 1.01–1.03 and 1.03–1.05 times, respectively. Therefore, the operating factor value may range from 1.115 to 1.274. The use of the operating factor in calculating the resistance of an earthing system by the induced potentials method increased the overall calculation accuracy, with the relative error not exceeding 3%. This corresponds to the normative and technical requirements stipulated by the Federal Grid Company of the Unified Energy System of Russia.