变电站外短路时架空地线分流系数的计算方法

Calculationmethod of Shunt Coefficient of Overhead Ground Wire During Short Circuit Outside Substation

变电站外发生短路故障时流入地网中短路电流的大小决定了电力系统的安全性,准确的地网分流系数计算方法对实际工程设计有着重要作用。基于站外短路时电流分布的等效模型,得出了简化的站外短路时的分流阻抗电路,结合回路电流法推导出了地网分流系数的计算公式,并利用Mathematica软件实现了求解过程。针对某变电站短路模型,分别用CDEGS软件与本文的回路电流法模型对分流系数进行了计算,计算结果显示误差在10%以内,符合工程计算要求,体现了计算结果的工程实用价值。分析了变电站接地电阻架空地线型号、杆塔电阻、档距与档数对地网分流系数的影响,最后提出了降低地网入地电流的合理性措施。

The safety of substation is determined by the magnitude of short-circuit current when short-circuit fault occurs in substation.Based on the equivalent model of current distribution in off-site short-circuit,the simplified shunt impedance circuit in off-site short-circuit is obtained.Combined with the loop current method,the calculation formula of shunt coefficient of ground network is derived,and the solution process is realized by Mathematica software.For the short-circuit model of a substation,the shunt coefficient is calculated by using CDEGS software and the loop current method model in this paper respectively.The calculation results show that the error is less than 10%,which meets the requirements of engineering calculation and reflects the engineering practical value of the calculation results.The influence of grounding resistance of substation,type of overhead ground wire,resistance of tower,distance between gears and number of gears on shunt coefficient of ground grid is analyzed,and some reasonable measures to reduce the current into ground grid are put forward.