Equivalent circuit approximation of transformer insulation by using PDC measurement

This paper represents the insulation model of 3φ, 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 C50 Hz, R0, R 1 and C1 in series, R2 and C2 in series, R3 and C3 in series, and R4 and C 4 in series. C50 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 (R1 and C1) 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 C50 Hz of 3.643 nF, R0 of 334.8 GΩ. The values of R 1-R4 are 86.52, 110.5, 669.5 and 271.0 GΩ 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. © 2008 IEEE.