Study On Transformer Protection Based On Winding Loop Equilibrium Equation

Transformer, as one of the most important and costly major apparatuses in the power system, is the hinge to transform electric energy in different voltage, whose running state will affect the safety and stability of the power system. It should be set corresponding protection. Recently, transformer protection is always in poor performance, which is far less than line protection and generator protection, and exist unknown reasons mal-operate. The existing transformer protections haven't satisfied the demand of the power system. Therefore, research on more effective and more reliable transformer protection scheme is very important for improvement the performance of transformer protection.The paper firstly introduces the existing transformer differential protection and its shortage, and summarizes the new ideas of transformer main protection.The shortage of existing transformer protection principle based on the transformer model is analyzed, and which stems from ignoring the effect of three-phase unbalance winding in delta side to winding loop is be pointed out. Based on the loop equations of transformer, utilizing the unbalance current in the delta windings to contact the three phases loop equations, the winding loop equilibrium equation model represented the normal running transformer is obtained. The novel model takes into account the impact that a random phase of delta windings acts on the other two phases of primary and secondary windings. According to the characteristic that the equation is not valid while the winding parameters change due to the occurrence of internal fault, a novel transformer protection principle based on the winding loop equilibrium equation and its criteria are proposed.The key problem of realizing the novel transformer protection principle is how to obtain accurate parameters of winding loop equilibrium equation. On account of more parameters information getting from the physical characteristic and data plate of transformer, constrained least squares algorithm is put forward to estimate the parameters.For the demand of transformer protection research, on the basis of analyzing and summing up previous experience, digital simulation model and dynamic imitation model are established, and the representative running states of transformer are simulated, recording the voltage and current data. Adopting the simulated data to verify the proposed principle, good performance is shown from the calculated results.