Comparison of Transformer Detailed Models for Fast and Very Fast Transient Studies

The fast and very fast transient overvoltages can endanger the insulation of transformer windings. Therefore, it is necessary to develop models, to study these transients. This paper compares the two well-known multiconductor transmission line (MTL) and lumped parameter detailed (RLC ladder network) models. The high-voltage (HV) winding of a 220/35-kV, 50-MVA transformer has been modeled using these models. The simulation results of the MTL and the RLC ladder network models have been compared with the measurements results in the frequency domain, by application of the Pearson´s correlation coefficients. It is shown that the RLC Ladder Network model should be used for fast transient overvoltage (FTO) studies, i.e. frequency range of 10 kHz < / < 1 MHz and the MTL model with frequency dependent loss factor, demonstrates a better agreement with the measurement results for very fast transient overvoltage (VFTO) studies, i.e., in the frequency range of 1 MHz les / les 5 MHz.