LAUSR

For converter transformer, current differential protection fails to operate in the case of internal fault occurs during dc bias or inrush current. Therefore, a new criterion is proposed in this paper to construct a new differential protection scheme. The new criterion is established by the ratio of wavelet energy entropy (RWEE) of current fault component on the primary to that on the secondary side. Once an internal fault occurs, the energy entropy (WEE) of the primary side is much larger than that on the secondary side, and then a large RWEE can be obtained. Otherwise, WEE of both sides are similar, and RWEE is around one. The simulation results show that the proposed criterion can perform well under inrush current, CT saturation, and dc bias conditions. It can discriminate the internal fault from external fault. Most importantly, it avoids the refusal of tripping when an internal fault occurs.