Power transformer transient modeling using frequency response analysis

Vector Fitting is employed to approximate the Frequency Response Analysis (FRA) measurement data of a 13.8 kV/136.8 kV, 50-MVA single phase transformer. The frequency response of the primary and secondary coils as well the coupling between the coils have been measured in the frequency range of up to 2 MHz. The measured data includes the stray capacitances that exist between the coils. A circuit synthesis model is used to represent the measured data in the form of a two-port passive RLC network. The derived network is implemented in a commonly used power system transient simulator (PSCAD/EMTDC). The proposed RLC model is passive to ensure the stability of the network. The model can be used to investigate transient response of the transformer including the simulation of switching and lightning overvoltage transients. The results are compared with those derived from existing simple models.