Equivalent circuit approximation of transformer insulation by using PDC measurement

This paper represents the insulation model of 3Phi, 50 MVA, 132.8/13.8 kV power transformer. This model is developed from the polarization and depolarization current measurement (PDC). The insulation modeling consists of a parallel circuit among C_{50 Hz}, R₀, R₁ and C₁ in series, R₂ and C₂ in series, R₃ and C₃ in series, and R₄ and C₄ in series. C_{50 Hz} is obtained from the conventional measurement method; whereas, the applied step voltage and the sum of PDC are calculated for R₀. The individual elements (R_i and C_i) are determined from fitting technique employing MATLAB program. From experimental results of the tested transformer, the example of insulation model for Transformer No. 1 (T1) is created with C_{50 Hz} of 3.643 nF, R₀ of 334.8 GOmega. The values of R₁-R₄ are 86.52, 110.5, 669.5 and 271.0 GOmega respectively; while, the values of C₁-C₄ are 37.62, 6.047, 0.101 and 0.013 nF respectively. The proposed model is validated by calculating dissipation factor and measuring dissipation factor. The results show that the proposed model and experimental validation are good agreement with each others.