Abstract
This paper presents an analysis of a very fast transient overvoltage (VFTO) experienced by a 550-kV gas-insulated substation (GIS) that caused the failure of a disconnector switch (DS) and circuit breaker (CB), after manual closure of the DS. Simulations were performed using an electromagnetic transient program with GIS component modeling for high-frequency analysis and multi-spark electric-arc modeling. The simulation results were verified by comparison with field test measurements and showed an acceptably accurate waveform and amplitude prediction for VFTO on the 550-kV GIS under study, allowing for improved failure analysis. The simulation results using equivalent electrical circuit models indicated that the failures occurred at a voltage below the lightning impulse withstand voltage (LIWV) with a high quantity of sparks. After the analysis, it was possible to conclude that the manual closure of the DS generated excessive sparks, causing significant damage to the fixed and mobile contacts and abnormal stress in the insulation of SF6 gas in the inhomogeneous electric field region of the CB, impacting on the reduction of the dielectric strength of SF6 gas, thereby producing a high-intensity arc between the shield and the enclosure.
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