Analysis of Very Fast Transient over Voltages in 150MVA 500KV Transformer by Using Wavelet Transform

This paper deals with analysis of VFTOs (Very Fast Transient over Voltages) in transformer, in this work the 150MVA, 500KV power transformer is considered and is designed by using MATLAB software of version 7. Very fast transient over voltages (VFTOs) generated by operating disconnections in gas insulated switch gear (GIS) could cause dielectric and mechanical stress and voltage oscillation inside the transformer connected. The situation is severer in the system that the main transformer is directly connected to GIS since the high frequency surges travel more easily along the coaxial gas insulated bus. The VFTOs in transformer windings have always been troublesome therefore it is important to analyze the wave both in time domain and frequency domain, therefore the wavelet transform is implemented. There are several works on vftos carried by many authors, but this method is efficient and can be used to compute the effect of VFTOs in transformer there by necessary methods of suppression can be implemented to reduce the effect of very fast transient over voltages in the transformer