Reascher On Novel Transformer Protection Based On Flux Linkage Balance Equation

Transformer plays an important role in power system, as well as the transformer protection is a vital part of power system protective relaying. The traditional differential protection, which is based on the Kirchhoff’s Law, suffers from the disadvantage of the electromagnetism coupling characteristic of transformers. Due to the electromagnetism coupling characteristic and the complex magnetic circuit, the Kirchhoff’s Law is not available, which affects the reliability of transformer current differential protection and even the stability of electric power system.A novel three phase transformer protective principle and criterion, which is not effected by the inrush current, of transformer based on flux linkage balance equations, which employs the equivalence circuit model of transformer, is presented in this paper. The discriminative criterion is established by eliminating the flux linkage in the flux balance equations using the Gaussian elimination method. The method of setting threshold value is given based on the turn to turn fault analysis. In addition, the protective criterions of three-phase transformer with varied connection are described as well.The precisely parameter estimation of transformer winding is one of the most important techniques of this protection principle. The Least Square method is utilized to parameter estimation, however the accuracy and converge rates are dependant on the width of time window. The most appropriate time window width is analysed for the advanced the converge rate and accuracy of the Least Square method.The protective scheme based on the flux linkage balance equation is also presented, which can implement the protection of transformer. The performance of the transformer protection is proved that the new criterion is not sensitive to inrush current, fault types, system closing angle, and transition resistance and so on, by the ATPDraw and Matlab simulations associated with single-phase transformers and three-phase transformers.This paper creatively attempts to study a novel principle of transformer protection for power system. Nevertheless, there are still more continue works to do for consummating this protection principle, such as testing the effect of local disturbance, consummating the arithmetic and advancing the action time of protection.