Flashover Analyses of 500 kV Transmission Towers with Capacitive Grounding Resistance

Abstract

Abstract:Grounding resistances of transmission towers in Japan are commonly required to be less than 10 ohm to avoid lightning back flashover accident. The surrounding soil, therefore, must be improved by chemical or construction ways if the resistance are much higher than the recommended value. In order to reduce the cost of these works, the authors have investigated on flashover simulation with various grounding conditions. In this paper, we propose the particular model for grounding resistance concerning the impulse characteristics of an actual 500kV-transmission tower footing base. We also present the results of the EMTP simulations with the proposed model, where the results suggest that it be not always necessary to limit the grounding resistance less than 10 ohm and it may be possible to reduce construction cost for transmission towers.

Sensitivity Analysis on Grounding Models for 500kV Transmission Lines

“…The initial resistance measured in capacitive transient since a timedependent impedance curve sometimes starts at a certain value in spite of zero impedance. We also measured such a phenomena in our previous experiment [8], where the ratio of R; to Rp was 0.75. This is also unpredictable parameter without practical measurements in advance.…”

“…Thus, in this paper, we will make the sensitivity analysis of the ionization gradient E, in the grounding impedance model. In other words, we will exam how the back flashover accident would be influenced by the value of E, <2.3> Capacitive impedance model Several reports including our previous experimental result [5], [8] indicate that capacitive characteristics are often measured in the grounding impedance on high-resistivity soil. Table I Examining models and parameters model.…”

Lightning back flashover tripping patterns on a 275/132 kV quadruple circuit transmission line in Malaysia

“…Previous researches show great concern on the back flashover phenomena since a great number of lightning strikes were recorded terminating on the tower and shield wire rather than the phase conductor. Extensive numerical simulations by means of Electromagnetic Transient Program (EMTP) have been carried out on back flashover phenomena affecting overhead transmission lines [7][8][9][10]. In the case of effectively shielded lines, the surge voltage caused by back flashover is also usually more severe than those caused by shielding failure and induced overvoltage.…”