Transient modeling and analysis of transformer windings under VFTO

Calculation of over-voltage distribution of transformer windings under Very Fast Transient Over-voltage (VFTO) is very important to insulate design of transformers windings. In order to investigate over-voltage distribution under VFTOs, a proposed model using lumped-parameter components is presented in this paper. In the case of easily destroyed former several windings, each winding is modeled as one unit; other windings are modeled using two windings as one unit. Then mathematic model based on MTL (Multi-conductor Transmission Line) Model and boundary conditions is recommended. Eventually transient over-voltage distribution of practical transformer is calculated using FDTD (Finite Difference Time Domain) method. Computational results are consistent with Electro-magnetic Transient Program (EMTP), so feasibility and validity of this method is validated.