利用MOV限制变压器绕组的特快速暂态过电压研究

Study on Limiting Very Fast Transient Overvoltage of Transformer Winding by MOV

气体绝缘金属封闭式组合电器(gas insulated substation,GIS)中的特快速暂态过电压会对电力系统的稳定性和变压器绕组的绝缘防护造成极大的损害。变压器的绝缘设计通常只考虑雷电过电压和操作过电压,而常忽略特快速暂态过电压(very fast transient overvoltage,VFTO)对变压器的冲击作用,金属氧化物避雷器(mental oxide varistor,MOV)因其良好的非线性特性而被用于改善绕组电位分布。基于此研究了变压器绕组两端并联MOV前后电压分布和电压梯度分布来探究MOV用于防护过电压的可行性。首先,提出了改进的时域有限元法,建立了变压器绕组并联MOV前后的多导体传输线模型;然后,推导了基于单变量时域有限元法求解该模型的边界条件;最后,通过MATLAB仿真计算了变压器绕组并联MOV前后的电压分布和电压梯度大小,验证了所采用的计算模型和计算方法的正确性,同时也证明了在VFTO作用下用MOV保护变压器绕组的可行性。

Very fast transient overvoltage(VFTO)in gas insulated substation(GIS)will cause great damage to the stability of power system and the insulation protection of transformer winding.The insulation design of transformers usually only considers lightning overvoltage and operating overvoltage,and often ignores the impact effect of VFTO on transformers,and mental oxide varistor(MOV)is used to improve winding potential distribution because of its good nonlinear characteristics.This paper studies the voltage distribution before and after the parallel MOV at both ends of the transformer winding to explore the feasibility of MOV for overvoltage protection.Based on the finite element time domain(FETD),the multi-conductor transmission line before and after the parallel MOV of transformer windings is established,and then the boundary conditions of solving the model based on the FETD are deduced.Finally,the voltage distribution and voltage gradient before and after the parallel MOV of transformer windings are calculated by MATLAB,which verifies the correctness of the calculation model and method.At the same time,it also proves the feasibility of using MOV to protect transformer windings under VFTO.