Transient analysis of transformer windings based on Finite Different Time domain method

Calculation of over-voltage distribution of transformer windings under very fast transient over-voltage (VFTO) is very important to insulate design of transformer windings. In order to investigate over-voltage distribution of transformer windings under VFTOs, firstly in the case of easily destroyed former several windings, each winding is modeled as one unit, others are modeled using two windings as one unit, then a model of transformer windings based on multiconductor transmission line model (MTLM) is developed and calculated based on finite-difference time-domain method(FDTD). Secondly, vector fitting method is adopted to deal with frequency-dependent parameters by expanding time-domain form of internal impedance of transformer windings into a sum of finite exponential function, which is easy for time-domain convolution. An actual autotransformer windings model is studied, calculated results based on FDTD method are consistent with electromagnetic transient program (EMTP) simulation results.