Simulation of mitigation methods for VFTO' sand VFTC's in Gas Insulated Substations

Switching operations of circuit breaker, disconnector and fault conditions in a Gas Insulated Substations (GIS) leads to Very Fast Transient Over voltages (VFTO) and Very Fast Transient Currents (VFTC) are developed. These VFTO's and VFTC's leads to generation of Electromagnetic fields in a gas insulated substations. These Electromagnetic fields due to VFTO's and VFTC's leads to greater damages on the insulation of equipments like power transformers, bushings, spacers etc. connected in the GIS system. These transient rise times are in nanoseconds range and the oscillations are in the MHz frequency range To evaluate the magnitudes at various locations, it is required to perform an accurate analysis on the wave shape and amplitudes of VFTO and VFTC. In this paper the component models of more accurate 420kV GIS station is considered for simulation and analyzed magnitudes at different points in the 420kV GIS, proposed the effective mitigation method to reduce the amplitude of the VFTC and VFTO is presented. Simulations are performed with more accurate modeling of 420kV GIS system model. Electro Magnetic Transient Programming (EMTP) is used to analyse the VFTO's and VFTC's at the different locations in the GIS system. Simulation results are represented for various types of suppression methods considered for analysis.