The calculation of the voltage distribution in transformer windings under VFTO based on FDTD method

In order to study the voltage distribution in transformer windings under Very Fast Transient Overvoltage (VFTO), a model for transformer windings has been developed based on Multi-conductor Transmission-Lines (MTLs) theory and the computing equations of the model based on Finite-Difference Time-Domain method(FDTD) is deduced. The Vector Fitting method is adopted to treat the frequency-dependent parameter by expanding the time-domain form of internal impedance of the transformer windings into a sum of finite exponential functions which are easy for the time-domain convolution. For validation, an actual transformer winding model has been studied. The calculated result are compared with the measured result and a satisfactory result is obtained.