变电站地电位升对低压避雷器的反击仿真研究

Backflash Simulation Research on Substation Ground Potential Rise to Low Voltage Arrester

变电站地电位升(GPR)是接地系统设计中重要的安全性指标,其限值的确定受高土壤电阻率和大故障电流等因素的严重制约,致使接地电阻难以达到要求,同时过高的GPR易使一次设备中反击耐受能力最弱的低压避雷器遭受损坏。首先指出利用传统过电压方法选取避雷器的不足,并通过电磁暂态计算程序ATPdraw建立反击模型,以常用的6 kV和10 kV无间隙金属氧化物避雷器作为研究对象,对短路故障时的放电电流、吸收能量和不同线路长度对地电容对GPR的耐受能力均进行了仿真。结果表明:当线路对地电容为6μF时,分别布置6 kV和10 kV两种低压避雷器,其承受的GPR限值为8.3 kV和11.83 kV;短路电流直流分量使放电电流瞬间达到峰值,短期内吸收的能量易超过耐受极限;采用多组避雷器并联能提高GPR限值,但随并联组数的增加提高效果将不再显著;线路对地电容的增加使GPR耐受值呈线性递减。

Substation ground potential rise(GPR)is an important safety indicator in the design of grounding systems.The determination of the limit is severely restricted by factors such as high soil resistivity and large fault current,which makes it difficult to meet the requirements of grounding resistance and excessively high GPR is easy to damage the low-voltage arrester with the weakest back-tolerance in the primary equipment.The auther points out the shortcomings of the traditional overvoltage method to select the arrester,and establishes the counterattack model through the electromagnetic transient calculation program ATPdraw.Taking commonly used 6 kV and 10 kV gapless metal oxide arresters as research objects,and the discharge current in the case of short circuit fault,the ability to absorb energy and different line lengths to ground capacitance to GPR is simulated.The results show that when the line-to-ground capacitance is 6μF,two low-voltage arresters of 6 kV and 10 kV are respectively arranged,and the GPR limits are 8.3 kV and 11.83 kV.The short-circuit current DC component makes the discharge current instantaneously peak and absorbs in a short time.The energy easily exceeds the tolerance limit;multiple sets of arresters in parallel can increase the GPR limit,but the effect of increasing the number of parallel groups is no longer significant;the increase in line-to-ground capacitance makes the GPR tolerance linearly decreasing.