ZnO lighting arrester earthing impedance characteristics under transient overvoltages

Abstract

Lightning arrester in a power system is categorized as a device, which operates in transient conditions. Therefore, the performance of the arrester must be analyzed in transient circumstances. Some particular considerations such as physical (grounding installation) and electrical (impulse current) aspects must be taken. Hence, this research aims to take into account the effect of nonlinear characteristics of the grounding impedance on the residual voltage of the lightning protection system in different discharge conditions. In this issue, the lightning protection system consisting of ZnO and grounding model was adjusted to yield the accurate results in EMTP. For this purpose, IEEE dynamic model of ZnO arrester was adjusted such that the manufacturer's performance test results are achieved. The arrester was connected to the improved circuit model of the grounding electrode system. To analyze the performance of the lightning protection system with different grounding configurations, the system was subjected to the three groups of lightning impulse currents. For this purpose, CIGRE standard, Berger, and 8/20 (µs/µs) standard lightning currents were applied as impulse currents. The results shown that the lightning protection system cannot completely protect the power system equipment during the high amplitude and very fast front times of discharge currents, which were experienced under CIGRE and Berger current. In addition, residual voltages of the lightning protection system under standard performance tests for discharge currents less than 5kA do not exceed the protection level, but compare to the manufacturer’s results, the residual voltages are considerably increased.