抑制发电厂短路电流引起地网电位差的措施分析

Measures to Reduce the Ground Potential Difference due to Short Circuit Current in Power Plants

大型发电厂发生短路故障时短路电流沿着接地网回流至发电机中性点,造成很高的网内电位差,严重影响二次系统等厂内设备的安全运行。在某水电站通过人为在其开关站向接地网注入电流、在发电机接地点处抽出电流,来模拟实际短路情况,现场测试了接地网上的地电位差,评估了实际短路故障下接地网上的最大电位差。进一步建立了该水电站的立体接地网模型,通过仿真计算,研究了降低开关站短路故障产生的接地网内电位差的措施。研究发现,发电厂内发生短路故障时,短路点和发电机厂房之间的地电位差最大。在电缆沟内增设多根间距20cm以上的铜排,可以有效降低地电位差。

When a short-circuit fault occurs in a large power plant, the short-circuit current flows back to the neutral point of the generator along the grounding grid, resulting in a high potential difference in the grid, which seriously affects the safe operation of the secondary systems and other equipment in the plant. This paper carries out the short circuit simulation experiment at a large hydropower plant by artificially injecting a current into the grounding grid at its switching station and drawing it out at the generator grounding point. The ground potential difference on the grounding grid is tested on-site and thus the maximum potential difference on the grounding grid under the actual short-circuit faults is evaluated. The paper further establishes the three-dimensional grounding grid model of the hydropower plant. Through a numerical simulation, the measures to reduce the potential difference in the grounding grid caused by the short-circuit faults at the switching station are studied. The study finds that when a short-circuit fault occurs in the power plant, the largest ground potential difference lies between the short-circuit point and the generator building. Adding multiple copper bars with a spacing of more than 20 cm can effectively reduce the ground potential difference along the cable trench.