特快速暂态过电压作用下变压器绕组内置MOV动态保护特性

Dynamic Protection Characteristic of MOV for Transformer Windings Under VFTO

特快速暂态过电压(VFTO)是由气体绝缘变电站开关操作产生的一种陡波前过电压,它的直接入侵会对变压器绕组的纵绝缘造成极大危害。本文通过理论分析、数值计算和实际测量研究了VFTO作用下变压器绕组并联MOV的保护特性。本文首先建立了变压器绕组的多导体传输线模型(MTLs),推导了基于时域有限差分法(FDTD)的求解迭代公式,通过应用矢量匹配法逼近传输线频变阻抗,解决了时域有限差分法难以处理参数频变效应的问题。然后,建立了变压器绕组并联MOV的多导体传输线模型,并推导了基于FDTD求解该模型的迭代公式。最后,研究了一个连续式变压器绕组模型,测量并计算了该模型在VFTO作用下并联MOV前后的电位分布。对测量结果与计算结果的分析和比较不仅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） is a kind of switching impulse overvoltage with very steep front caused by the switching operation in gas insulated substation. Its directly invading to transformer windings may severely damage their longitudinal insulation. In this paper, the protection characteristic of the MOV in parallel with transformer windings under VFTO is studied. First, the multi-conductor transmission lines （MTLs） model for transformer windings is setup, the iterative computing equations based on the finite-difference time-domain method （FDTD） are deduced, and the vector fitting method is adopted to treat the frequency-dependent parameter. Second, the model of the transformer winding in parallel with MOV based on MTLs is developed, and the computing equations to solve the model based on FDTD are deduced. Finally, a practical transformer winding model is studied, the voltage distribution of the transformer windings under VFTO with and without MOV are measured and calculated respectively. The comparison between the calculating results with that of measuring not only indicates the validity of the model and computing method, but also proves the feasibility of using MOV to protect transformer windings from VFTO.