Numerical simulation and analytical calculation of the GIS transient enclosure voltage interaction with grounding system

Abstract

Gas-insulated substations (GISs) are widely used in power systems due to high reliability, convenient maintenance, and small area occupation. Transient enclosure voltage (TEV) is a consequent effect of very fast transient overvoltage (VFTO) during the switching operations in GISs. It can lead to insulation degradation, damage to the secondary equipment connected with the shell of GIS, and harm to the working staff. This paper presents a correlation between a lumped-circuit model based on transmission line theory (TLT) for purpose of the simulation and an analytical approach based on the scattering matrix for the evaluation of TEVs. Furthermore, a frequency-dependent model is proposed to quantify the transient grounding impedance (TGIM) against the waves with high-frequency content such as TEVs. The interaction between the TEV and the grounding system has been investigated analytically, and experimentally based on the field measurements in other efforts. The comparisons indicate that the modified wide-band TGIM results in an improvement in comparison with the other works to track both the front and tail of a measured voltage-wave within acceptable accuracy. Furthermore, the role of the ground strap as a damping structure using a modified model on TEV profile has been scrutinized regarding the grounding system model and the rising rate of TEVs. It is indicated that considering frequency-dependent TGIM could lead to a 25% variation in the estimation of amplitude of TEVs.