季节性冻土地区变电站地网入地故障电流分析及其限制措施研究

季节性冻土地区,冬季土壤冻结后,其电阻率急剧增加,不仅导致接地电阻上升数倍,同时会引起变电站内部短路时流入地网的故障电流发生变化。文中研究了季节性冻土地区土壤冻结深度对地网分流系数的影响规律。首先建立了季节性冻土地区的土壤结构模型,根据土壤的冻结规律,改变土壤的结构与电阻率,仿真得到了不同情况下变电站地网入地短路电流的分配规律。研究发现:由于杆塔的接地体埋深要小于地网的埋深,杆塔接地装置受冻土影响更大,导致变电站分流系数急剧增加,甚至超过50%,使得原有地网设计无法满足安全标准;仅对地网增设垂直接地极降阻会导致其分流系数的增大,变电站进出线路的临近6~7基杆塔的接地是影响变电站分流的主要因素,因此可以通过对其增设垂直接地极或加大埋深的方式来降低地网分流系数,通过该方法可以提高季节性冻土地区地网的安全性能。

Analysis of the Fault Current Flowing into Substation Grounding Grid in Seasonal Frozen Soil Area

In seasonal frozen soil area, the soil resistivity increases rapidly after freezing, which leads to several times of increase in the grounding resistance, and the change of fault current flowing into grounding grid in the condition of short circuit in substation. In this paper, the influence of the depth of frozen soil on the shunt coefficient of the grid is studied. Firstly, a soil structure model of seasonal frozen soil region is established, and the distribution law of short circuit current of substation grounding grid is obtained under different conditions by changing the structure and resistivity of the soil according to its freezing law. The results show that: 1) the grounding electrode depth of tower is smaller than the burial depth of the grounding grid, so the frozen soil has a greater impact on grounding device, resuiting in a sharp increase in the shunt coefficient of grounding grid, even more than 50%, and the original design of grounding grid cannot meet the safety standards anymore;2) only adding vertical grounding electrodes to grounding grid will increase its shunt coefficient;and 3) the grounding device of 6-7 tower near the substation is the main factor affecting the shunt coefficient, so adding vertical grounding electrodes to the device and increasing the buried depth can reduce the shunt coefficient of grounding grid, and consequently improve the safety performance of grounding grid in seasonal frozen soil region.