Magnetic Balance Protection of Transformers Based on Optical Fiber Leakage Magnetic Field Measurement
Deng Xiangli1, Zhu Hongye1, Yan Kang1, Zhang Zhan1, Liu Shiming2
1. School of Electric Power Engineering Shanghai University of Electric Power Shanghai 200090 China; 2. School of Electric Power Engineering Shandong University Jinan 250061 China
Abstract：Traditional differential protection has difficulty responding effectively to early faults such as transformer winding deformation and minor inter-turn faults.Early winding faults can be sensitively detected according to the changes of transformer winding leakage field, but analytical methods and online measurement solutions suitable forwinding leakage field analysis of engineering applications are scarce. To address the above problems, this paper proposes a model for calculating the leakage field distribution of transformer windings under the simplified model, and puts forward a corresponding early fault protection scheme based on the magnetic balance principle of transformer leakage field. Firstly, the faulty winding with uneven current density distribution is divided into unfaulty turn winding and short-circuited turn winding by superposition theorem, and the Fourier series decomposition method is applied to the winding current density by using the mirror image current method and ignoring the effect of the core.For each frequency component, the leakage induction intensity is solved by the separation of variables method.The results of each frequency component are superimposed to obtain the spatial distribution function of the leakage induction intensity.Secondly, since the transformer winding, core and yoke are symmetrical in structure, the leakage field is symmetrically distributed in space. Magneto-optical sensors are set at the upper and lower end points and the middle of the winding, then the principle of magnetic balance protection based on transformer leakage field is proposed.When the transformer is in normal operation, the sum of radial magnetic induction intensity at the upper and lower end points of the winding is 0, and the radial magnetic induction intensity at the middle point is close to 0. If a fault occurs inside the transformer, the symmetry of the leakage magnetic field distribution changes, and a large amount of fault unevenness will appear at the upper and lower measurement points and the middle point, according to which early winding faultscan bedetected.Finally, the correctness of the magnetic balance protection scheme is verified by establishing the core simulation model of Ansys and the dynamic mode combined transformer model, and the advantages of magnetic balance protection under early faults are demonstrated by comparing the traditional differential protection with the method in this paper. The following conclusions are drawn from the simulations and dynamic mode experiments: (1) Based on three measurement points per winding, the transformer winding magnetic balance protection logic method can respond to the transformer winding early faults sensitively. (2) Magnetic balance protection is able to detect winding deformations above 5% and inter-turn short circuits below 1%. (3) The protection scheme is not affected by changes in load and inrush current.
邓祥力, 朱宏业, 严康, 张展, 刘世明. 基于光纤漏磁场测量的变压器磁平衡保护研究[J]. 电工技术学报, 2024, 39(3): 628-642.
Deng Xiangli, Zhu Hongye, Yan Kang, Zhang Zhan, Liu Shiming. Magnetic Balance Protection of Transformers Based on Optical Fiber Leakage Magnetic Field Measurement. Transactions of China Electrotechnical Society, 2024, 39(3): 628-642.
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2024, Vol. 39 
