Protective scheme for power transformers based on sequence power directions

A kind of feasible protective scheme for power transformers, quite different fault states, the scheme can distinguish internal faults, external faults and inrush current of transformers, which is based on various directions of sequence power. The detailed algorithm is as follows: Assume that the system integrative impedance angles are at the two sides of transformers as the operating sensitive angles. The positive and negative sequence powers at the primary side and the second side are all negative when there is an asymmetry fault in the protective zone. If an asymmetry fault is out of the protective zone, the positive and negative sequence powers at the fault side are positive while those at the other side are negative. Moreover, if the negative sequence power is much lower than the positive sequence power, conclusion of the symmetry fault can be drawn and under this condition, the fault type is judged only by the direction of the positive sequence power. If the positive and negative sequence powers at the second side of transformer are nearly zero, they can be taken as the magnetizing course of switching-on transformers. This scheme is quite sensitive to asymmetry faults. A lot of ATP simulations verity its correctness.