P. Valsalal, S. Usa, and K. Udayakumar
Finite Element Method, MOSA, stray capacitance, Very Fast Tran-sient Overvoltage
This paper studies the performance of Metal Oxide Surge Arrester (MOSA) for Gas Insulated Substation (GIS) applications. Few models proposed in the literature are used to describe the dynamic characteristic of the arrester and compared with experimental data to verify their accuracy. As percentage error is lesser in the case of a simpliļ¬ed IEEE model, for further analysis this model is chosen. MOSA of high-voltage rating have high stray capacitance, which cannot be neglected. The stray capacitance and zinc oxide block capacitance of the MOSA are calculated using Finite Element Method (FEM). In this study a 198 kV arrester is considered. By incorporating the effect of stray capacitance, we propose a new model. This model is analyzed for surges of different front times ranging from microseconds to nanoseconds. It is found that there is a delay to attain the initial peak value of residual voltage of the arrester due to the stray capacitance effect. The delay in the initial response time of the arrester may be one of the reasons for the failure of the arrester response in GIS when subjected to Very Fast Transient Overvoltage (VFTO). The use of guard rings allows delay due to the effect of stray capacitance to be minimized.
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