ISSN (e): 2250 – 3005 || Vol, 05 || Issue,02 || February – 2015 || International Journal of Computational Engineering Research (IJCER) www.ijceronline.com Open Access Journal Page 1 Continuous Wavelet Transform (CWT) based Analysis of Very Fast Transient over Voltages of 132 KV Power Transformer K.Prakasam 1 , D.Prabhavathi 2 , ,Dr.M.Suryakalavathi 3 , Dr.B.Ravindranath Reddy 4 1 Department of Electrical and Electronics Engineering, Sri Sivani College of Engineering,srikakulam,A.P,INDIA. 2 Department of Electrical and Electronics Engineering, Sri Sivani College of Engineering,Srikakulam,A.P,INDIA. 3 Department of Electrical and Electronics Engineering, JNTUH, Hyderabad,INDIA. 4 Department of Electrical and Electronics Engineering, JNTUH, Hyderabad,INDIA. I. INTRODUCTION Very Fast Transient Over voltages (VFTOs) generated by switching operations. This type of overvoltages is dangerous for the transformer insulation due to a short rise time, which can cause non-linear voltage distribution along transformer windings. In some special cases, the turn-to-turn voltage can rise near the transformer basic insulation level [1]. These problems can either lead to direct break down or initiation of partial discharge which deteriorate the insulation. After a short time this can result in an insulation breakdown. These over voltages occur inside the winding and are difficult to measure and detect. Electromagnetic transients may appear with a wide range of frequencies that vary from several Hz to several hundreds of MHz transients and faster electromagnetic transients. The latter type of transients can occur for a shorter duration ranging from microseconds to several cycles. Frequency ranges are classified into groups for the ease of developing models accurate enough due to frequency behavior of power components. An accurate mathematical representation of each power component can generally be developed for a specific frequency range (CIGRE, 1990). One of the reasons of generated VFTOs is re-strikes and pre-strikes during opening or closing of switching devices. Very Fast Transients (VFT), also known as Very Fast Front Transients, belong to the highest frequency range of transients in power systems. According to the classification proposed by the CIGRE Working Group 33–02, VFT may vary from 100 kHz up to 50 MHz (1990). According to IEC 71 –1, the shape of a very fast transient over voltage is ‗‗usually unidirectional with time to peak<0.1 ms, total duration<3 ms, and with superimposed oscillations at frequency 30 kHz<f<100 MHz‘‘ (1993). 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 but this method is efficient and can be used to compute the effect of VFTOs on transformer. In this paper a 132KV transformer is designed using Mat lab software of version 7.8, the VFTOs generated by switching conditions are calculated and are analyzed by wavelet transform and the result is tabulated and discussed. ABSTRACT This paper results the most accurate results of Very Fast Transient over Voltages of 132 KV transformer caused by the switching operation. A 132KV transformer is designed using MATLAB simulin, the VFTOs generated by the switching operations have been analyzed and are presented. The VFTOs generated due to Disconnector switching operation can cause insulation failure at very high voltage levels. The reasons of these problems are travelling waves which is generated during switching operations in a gas-insulated substation (GIS). Calculation of Very Fast Transient Overvoltage has been carried out using MATLAB7.8 for various switching. Keywords—disconnect or, High voltage level, MAT LAB, Switching, Switching operations, Travelling Very Fast Transient over voltages, Wavelet transform,