Study On The Methodology Of Winding Deformation Recognition For Converter Transformer

DC transmission system has a series of outstanding advantages including that the size and direction of the power can be adjusted quickly; that the stability level of power system can be improved; that the line corridors can be saved effectively and the, network losses can be reduced etc.. It is an important way not only to transmit power with high-voltage, large capacity and long-distance in the world but also to interconnect power grid. Converter transformer is the core equipment in the DC transmission system. Its safe and reliable operation has vital practical significance.The converter transformer works in special environment, and runs under the AC and DC excitation for a long time.Hence, the case of suffering short-circuit increased, and the probability of winding deformation is higher than that of the normal transformer. According to statistics, nearly 25% fault of the transformer caused by the transformer winding deformation. Converter transformer has special structure and connection mode, so there exists a wealth of high harmonics under normal operation.This paper analyzes several common winding deformation and the change characteristics of the corresponding parameters, summarizes the existing diagnosis of transformer winding deformation, and studies the special structure of converter transformer, its wiring and how it works. According to the structure of the converter transformer and its rich harmonics, this paper presents an on-line diagnostic method for winding deformation in converter transformer. The method removes the main magnetic flux which is nonlinear and has a great influence on the winding identification, and collects the real-time voltage and current of the converter transformer as the signal source, constructs the criteria matrix of winding deformation diagnostic denoted by structural parameters, and then generats the trend curve of the main characteristic parameters changing with frequency, finally, achieves the diagnosis of converter transformer by comparing the change of the main characteristic parameters under different frequencies. Laboratory tests confirmed that this method is effective and practical.