- The modeling of power transformer faults and its application to performance evaluation of a commercial digital power transformer relay are the objective of this study. A new method to build an EMTP/ATP power transformer model is proposed in this paper. Detailed modeling of the transformer relay is also discussed. The transient waveforms generated by ATP under different operating conditions are utilized to evaluate the performance of the transformer relay. The computer simulation results presented in this paper are consistent with the laboratory test result obtained using an analog power system model.