高压单芯电缆接地故障下的地电位升与护层工频过电压研究

Earth Potential Rises and Sheath Overvoltage in High-Voltage Cables Under Phase-to-Ground Fault

近年国内高压电缆线路外护层以及护层保护器击穿损坏的事故频发,为了优化电缆线路护层接地系统设计以及合理选择护层保护器,本研究基于PSCAD-EMTDC对110 kV纯电缆线路和架空线-电缆混合线路分别进行了仿真建模,分析了二者在单相接地短路故障情况下,采用各类护层接地方式的地电位升与护层工频过电压幅值特征,并探讨了电缆线路长度和接地电阻对护层工频过电压的影响,最终依据仿真计算结果提出了护层保护器的选用建议。研究结果表明:仅采用护层交叉互联的纯电缆线路和架空线-电缆混合线路,局部地电位升较小,最大护层工频过电压在4 kV~6 kV;纯电缆线路中护层单端接地段与交叉互联段的连接处以及架空线与护层单端接地的连接处存在严重的地电位上升,且受连接处接地电阻值影响明显,幅值可达24 kV,地电位升与感应电压的叠加使得护层工频过电压幅值远高于仅存在护层交叉互联的线路。研究结果可为电缆线路的护层接地系统设计以及护层保护器的选型提供参考依据。

Breakdown accidents of high voltage cable outer-sheath and sheath voltage limiters frequently occur.To improve sheath bonding system design and the selection of sheath voltage limiters,the author simulates 110 kV pure cable lines and hybrid overhead-cable lines using PSCAD-EMTDC.The amplitude characteristics of the earth potential rise and sheath overvoltage were analyzed when a single-phase-to-ground fault occurs in the case of various sheath bonding methods,and the influence of cable length and grounding resistance on sheath overvoltage were analyzed.The suggestion on the selection of sheath voltage limiters were put forward based on the simulation results.Simulation results indicated that the local earth potential rise was small for cross-bonded pure cable lines and overhead-cable lines,and the maximum sheath power-frequency overvoltage was 4 kV~6 kV.There existed a serious ground potential rise at the transition of cross-bonding and single-point bonding for pure cable lines,and the transition the overhead line and single-point bonding.Its amplitude was significantly affected by the grounding resistance at the transition,reaching 24 kV.The superposition of the earth potential rise and the induced voltage makes the sheath power frequency overvoltage much higher than lines with only sheath cross-bonded.The research results provide reference for the sheath bonding design and the selection of sheath voltage limiters.