10kV小电阻接地系统比值法则零序保护

Zero-sequence Protection for 10 kV Low-resistance Grounding System by Specific Ratio Value Rules

对于10 kV小电阻接地系统,目前主要采用定时限零序过流保护的定值需要躲过线路最大电容电流,难以反映高阻接地故障。通过分析多种接地故障的零序电流分布特点,寻找出表征故障的电流比值关系,构建一套比值法则,利用各10 kV出线及接地变压器中性点零序电流计算特征值,通过比较故障线路与非故障线路的特征值差异选出故障线路。比值法则可以通过特征值进行多种接地故障的保护,且能适应高阻接地故障情形。通过搭建PSCAD模型模拟高阻接地故障,获取单线单相及多线多相故障发生时零序电流的仿真数据,验证了使用比值法则进行故障判别的可行性。

For a 10 kV low-resistance grounding system,the setting value of the definite-time zero-sequence overcurrent protection method which is commonly used at present is necessarily higher than the line’s capacitive current,which cannot reflect the high-impedance fault.Through the analysis of the distribution characteristics of zero-sequence current under varying grounding faults,the relation between specific ratio values of current that characterize faults can be found to build a set of specific ratio rules,by which the specific ratio values related to the zero-sequence current of every 10 kV outgoing line and the neutral line in the grounding transformer are calculated.Afterwards,the specific ratio values of fault and normal branches are compared to determine the fault one.According to the specific ratio values,the pro⁃posed rules can protect against varying grounding faults,including the high-impedance grounding fault.A model is con⁃structed using PSCAD to simulate the high-impedance grounding fault,thereby obtaining the simulation data of zero-se⁃quence current under single-line single-phase and multi-line multi-phase faults.Simulation results verify the feasibility of using the specific ratio value rules to diagnose fault.