Simulation Of Optimal Mitigation Technique to Suppress the VFTOS In 1000KV EHV GIS Substations

Abstract

Equipment in the gas insulated substation will be harmed due to very fast transient over voltages which are generated by the switching operation of disconnector switches or circuit breakers. Constants restrike and prestrikes occur at contacts of disconnector switch during switching operation. Arcing currents travel across the contacts of disconnector switches due to these restrike and prestrikes leads to breakdown of the voltage. These arcing currents generate high frequency transients which reduces the dielectric strength of the elements of substations. The VFTO growth is characterized mostly by the maximum value of transients, frequency, and the quantity of incidents through the disconnector opening or closing operations. The frequency components of VFTO are related to the time duration of the voltage breakdown in SF6 gas and to the travelling wave conditions along the GIS. It is considered necessary to decrease VFTOs generated in GIS based EHV substation. In this paper, four techniques are examined to mitigate the VFTOs in 1000KV substation by simulating in MATLAB/SIMULINK tool. Limitations while doing experimental study on the substations can be overcome by some extent in simulation study. Results generated in simulation are tabulated in terms of peak value, rise time and settling time of oscillations.