EMTP Simulation of VFTO’s for 420 kV GIS

Abstract

Very Fast Transient Over voltages(VFTO) are generated due to switching operations and faults in a Gas Insulated Substation(GIS) needs lot of insight to safe guard the equipment and insulation of various systems. VFTOs can also cause malfunction of protection circuits and control circuits. These transients have traveling wave behavior; they travel to the external systems through enclosures, bushings, cable joints etc., and cause damage to the outside equipment. They can lead to secondary break downs in GIS and may give rise to electromagnetic interference. Thus it is important to develop a suitable simulation models for estimation of these over voltages. In order to estimate the over voltages, equivalent electrical network models are developed. This paper focused on 420 kV GIS system and equivalent model of GIS bus duct have been considered for the simulation of VFTOs. GIS equivalent models have been developed for various lengths of bus duct and simulations to estimate VFTOs are carried out with switching operations of Disconnector switch and fault conditions at various locations. The suppression of VFTOs are also simulated by inserting resistance across the disconnector switch. Comparison has been made in terms of voltage magnitudes with and without suppression methods. Significant reduction of voltage magnitudes are observed in this work. For simulation of equivalent GIS models Electro Magnetic Transient Programming (EMTP) is used.