Identification Of Parameters And The Transformer Relay Based On Parameter Identification

The differential protection has been the main protection technique for transformers. The correct discrimination between the inrush current and the fault current is crucial to the technique. However, by many factors, the differential protection can not completely avoid mal-operation. The algorithms based on equivalent circuit and characteristics of flux are not affected by the inrush and over-excitation current.They both can operate reliablely and quickly.However, the leakage inductance and resistance of each side of the thransformer are required as priori parameters.At present, there is no accurate algorithm on the identification of winding parameters. Only the sums of the parameters of the two sides can be got by the usual short-circuit experiment.So a new method is proposed to identify the parameters in this paper. The input signal and factors that influence the accuracy of identification are discussed. In order to verify the correction of this method, the identified parameters are used in the transformer protection based on the increment of flux linkages. The simulation results of EMTP and dynamic experiments show that the method can identify the parameters of each side accurately if use the correct input signal and parameters; when the identified parameters and the true parameters are applied to the transformer protection based on the increment of flux linkages, the two methods both can gurrentee it operate correctly.Finally, a transformer protection based on the parameter identification on line will be described in this paper. The program becomes to identifiy the parameters when the transformer is disturbed. Recursive damped least square which use the parameters identified off line as the initial parameters is proposed to identify the parameter on line.The inner fault can be detected because the leakage inductance will change when inner fault. It can act quickly and the threshold is very small.This protection has a good prospect. The simulation results of EMTP and dynamic eexperiments show that this protection can operate correctly under all situations.