This paper proposes a procedure for modeling various faults of power transformer including internal faults-turn to earth and turn to turn faults. The proposed modeling analyzes the behavior of the considered faults and studying their effect on the current of transformer in faulty winding in order to acquire possible accurate fault identification scheme. The fault detection process is dependent on the captured current signals that are employed with ATP simulator. Also, this study evaluates the impact of fault instant inception on the transformer voltage and current signals. Applications are carried out on a three phase two windings 4MVA, 15/6.9 kV, 50 Hz transformer in a distribution system. The employed simulations achieve accurate analysis with reliable decision for various critical conditions such as different fault ratios, different fault resistances, different fault inception time and different configuration of transformer winding connection.