Study On Differential Protection Algorithms Of Transformer On The Basis Of Wavelet Entropy

One of the most important equipments in the power system is transformer (an energy transfer element), the normal operation of which bears greatly upon the whole power system. In addition, large-size transformers are expensive. In the case of malfunctions, it is difficult to estimate economic damage incurred.After the analysis on the problems, which influence the transformer differential protection, this paper makes the following research. On the one hand, based on research of the mechanism of generating transformer inrush current and the characteristics and identification methods, the existing problems on the basis of the traditional principle for identifying inrush current are pointed out. On the other hand, when lightly internal short-circuit fault, restricted within rate restraint, the sensitivity of differential protection is unlikely to be very good.To improve the inrush current identification methods, based on research of wavelet analysis of digital signal (discrete wavelet transform etc.), the two method to identify differences between inrush and internal fault is proposed. And combining wavelet analysis with entropy theory, the two new-type protection criterion of formulas are presented. The simulation models of no load switching and turn-to-turn fault are established by MATLAB. Utilizing the two criterions of formulas of the two kind of wavelet entropy (wavelet energy entropy and wavelet time entropy), the disequilibrated current signals under the two abnormal operation conditions are analyzed, for verify them. Finally, combining wavelet energy entropy and wavelet time entropy, a new differential protection, for discriminate the light internal short-circuit fault from heavy inrush, is proposed. The results show that the new differential protection, based on wavelet entropy, can identify differences between inrush and internal fault reliably and rapidly.