Research On Transformer Protection Based On Parameter Identification

Transformer is one of the most important electrical equipment in power system. The safety operation of transformer affects not only the transformer's own safety, but also the security and stability of power system. The correct rate of transformer protection has remained at 70% to 80%, which was well below the correct rate of line and other equipment protection. More large capacity, high-voltage transformers were applied in power system, if a transformer was damaged by fault, there would be a range impact and it would be difficult to maintenance the transformer, this would bring serious economic losses. Considering these factors, the research for new transformer protection scheme with high performance, such as fast, reliable and sensitive, is very important.In this paper, the research object is electric power transformer protection. First, the transformer equivalent model is analyzed summarily, including equivalent T type circuit model, equivalentГtype circuit model and the loop equation model based on magnetic linkage conservation, then the transformer parameters is analyzed, including leakage inductance and excitation inductance. Second, the basic principle of parameters identification, the characteristic of parameters identification, the method of parameters identification are discussed. When the theory of parameters identification is applied to the transformer protection, three elements should be considered, including how to build the transformer model, the model's frequency band and the measure for parameters identification. This paper uses least squares method as the method of parameters identification. The identifiability of transformer parameters and the algorithm for identifying the leakage inductance of transformer are discussed.Transformer protection simulation system is built in PSCAD/EMTDC. An applied algorithm of leakage inductance identification is proposed based on preliminary simulation analysis, and then all transformer conditions are simulated, and using simulation data, leakage inductance is calculated. Finally, the transformer protection scheme based on the leakage inductance identification is designed.