Mutual Inductance Analysis of Overhead Lines During Grounding Impedance Measurement

Large grounding devices using overhead lines to measure grounding impedance have the problem of difficulty in accurately assessing line mutual inductance. To address this problem, firstly, a theoretical model of arbitrary line mutual inductance during grounding measurement is derived theoretically, and a numerical calculation scheme for the line mutual inductance model is proposed based on the Heppe mutual inductance calculation formula and the complex image method. Secondly, the application of the thesis method is realized using an actual measurement case of a 500 kV power station and the results are compared with those of three other different penetration depth approximation formulas. The results show that care must be taken when using the line for grounding measurements because earth loss can cause the line mutual inductance angle to be less than 90 degrees. The thesis method is a rigorous benchmark method, and the only other method that can be used for mutual inductance analysis when measuring grounding impedance on overhead lines is the Deri penetration depth formula, which deviates by about 3% on engineering cases. The thesis method helps to fundamentally remove the error caused by the mutual inductance factor of leads in grounding measurement, and provides a valid reference for accurate grounding impedance calibration.