城区变电站地线分流特性对接地网设计影响的分析

Influence of Fault Current Division Characteristics of Urban Substation on its Grounding Grid Design

接地网安全性评估工作已延伸到接地网的前端设计阶段,由于变电站站址土壤条件、接地网拓扑结构和短路电流水平几个因素共同决定了接地网的安全性,而地线分流较大程度地改变了实际入地短路电流水平,进而对接地网特性参数水平产生很大的影响,是接地网设计和接地阻抗取值中需要重点考虑的因素。纯电缆出线的城区变电站具有与常规架空出线变电站不同的地线分流特点,通过具体设计案例,介绍了地线分流影响的分析方法,指出城区变电站地线分流水平偏低,入地短路电流水平偏高的特点,对接地阻抗的要求更为苛刻,在接地网设计中,不能满足于接地阻抗满足传统设计值要求,还必须准确核算电缆外护套的分流系数,基于接地网安全性科学地选择接地阻抗设计值。

Nowadays, the grounding grid security evaluation has extended in the stage of grounding grid design. The security of the grounding grid depends upon the soil condition where the substation located, the topology structure of the grounding grid and the short circuit current levels. In fact, the allowed grounding current level is determined by the shunting capability of the grounding condvctors and will greatly influence the grounding grid characteristic paromeiers.So such shunting case is emphatically paid attention to the grouitdmg grid design and grounding impedance choose. The grounding conductor in urban substation with cable as feed out line may have different current shunting features with that in substation with overhead feed out line. In this paper, through practical design case, the analysis method of grounding conductor shunting effects is introduced. It points out that the shunting level in urban substation is lower, and the grounding short circuit current is higher, which results in higher requirement to grounding impedance. Such case can＇t meet the traditional design value of the grounding impedance. The shunting coefficient of the cable outer shielding layer should be checked and the grounding impedance designed value must be chosen based on the security of the grounding grid.