基于光纤漏磁场测量的变压器磁平衡保护研究

Magnetic Balance Protection of Transformers Based on Optical Fiber Leakage Magnetic Field Measurement

针对变压器绕组变形、轻微匝间故障等早期故障,传统的保护方案一般难以进行有效的诊断,根据变压器绕组漏磁场变化可以灵敏地检测出绕组的早期故障,但缺乏适用于工程应用的绕组漏磁场分析的解析方法和在线测量方案。针对这些问题,该文计算了简化模型下的变压器绕组漏磁场分布,通过测量绕组上、下表面和中部的漏磁感应强度,提出故障分量磁平衡保护的整定方法和判别逻辑。最后,建立了Ansys的仿真模型和动模实验模型,验证了保护方案具有不受负荷变化及不受励磁涌流的影响,并且区内故障检测灵敏度高的优点。

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.