Research On Substitution Waveform Of VFTO

In GIS, very fast transient overvoltage is dangerous to the insulation of high-voltage electrical equipments like transformer. So insulation experiment and stimulation need to be done before the electrical equipment applied. There are few accurate VFTO substitution waveforms currently. In this paper, the VFTO substitution waveforms are studied, which provides more accurate input of VFTO for high-voltage stimulation.In this paper, the internal models of GIS are established respectively for 500kV, 750kV, 1000kV voltage level. By changing lines, component parameters and operation, a large number of VFTO waveforms are received at the entrance of transformer under various voltage levels. Referring to the method to get the amplitude of lightning, the amplitudes of VFTO are counted by SPSS by calculating the cumulative probability and density curves of VFTO, the amplitude is corresponding to 99% of the probability density. The substitution waveform of VFTO presented considers the amplitude, frequency, frequency weighting. The method to get them is discussed in this paper. Then the VFTO substitution waveforms under various voltage levels are produced. There is a comparison between the simulated waveforms and substitution waveforms whose effect to transformer windings. From the results, it can be clearly found that the waveform proposed in this paper can replace the VFTO at the entrance of transformer. According to the given VFTO of the entrance of voltage transformer, apply the calculation method of substitution VFTO wave at the entrance of transformer. Calculate the substitution VFTO wave at entrance the voltage transformer. Use the substitution wave and VFTO wave as input to the voltage transformer to calculate the interference voltage of secondary port. From the results, we can see that it is possible to use the substitution waveform to calculate the influence to secondary circuit.