Estimation and Analysis of VFTO at Various Locations in 132kV GIS Substation

Gas Insulated Switchgear Substation (GIS Substation) has high reliability, easy maintenance, less area requirement etc. Due to this, it has found wide range of application in power system sector over last few decades. But the unique problem with GIS substation is generation and propagation of very fast transient overvoltage (VFTO) due to switching operation of circuit breaker, disconnector switches or due to earth faults. The generated VFTO causes stress on the insulation of equipment's like power transformer, bushings, spacers etc. connected to the GIS. The origin of VFTO, its propagation and impacts on GIS have been discussed in this paper. In this paper the components of 132 kV GIS substation is modelled more accurately and considered for simulation. Electromagnetic Transient Program (EMTP-RV) software is used for the simulation for various switching condition. The variation in VFTO magnitude along the GIS bus nodes for different magnitudes of trapped charge has been studied. The VFTO peak along the GIS bus nodes during circuit breaker operation and disconnector operation is compared. The results show that VFTO magnitudes are higher along the GIS bus nodes in case of circuit breaker operation as compared to disconnector switch operation. The results also show that the increase of trapped charge on the line increases the VFTO levels.