基于剩余电流和不平衡电流突变向量比的TN-C-S系统漏电故障检测方法

Leakage Fault Detection Method for TN-C-S System Based on Residual Current and Unbalanced Current Mutation Vector Ratio

TN-C-S系统在我国应用广泛,但由于固有剩余电流大,无法区分负荷投切和故障引起的剩余电流变化,漏电总保和中保无法投运,存在安全隐患。针对该问题,提出一种基于剩余电流和不平衡电流突变量之比的漏电故障保护方法。首先,分析剩余电流回路,剩余电流和不平衡电流突变量之比在单相接地故障发生时刻突变,在负荷投切时不变。其次,基于中性线阻抗和接地阻抗不会发生突变的特征,计算故障电流突变量幅值,以故障电流突变量幅值越限作为故障判别依据,实现漏电故障检测。仿真及试验证明,所提方法可有效区分负荷投切和漏电故障,实现大幅值固有剩余电流下的漏电故障检测,在单支路和多支路系统中的检测灵敏度分别为70、150 mA,满足TN-C-S系统多级漏电保护的灵敏度要求。

TN-C-S system is widely used in China.Due to the large inherent residual current and the difficulty in distinguishing the residual current mutations caused by load switching or faults,level 1 and 2 leakage protection cannot be put into operation.Serious safety hazards exist in TN-C-S systems.To solve this problem,a leakage protection method based on the ratio of the residual and unbalanced current mutation vectors is proposed.First,the residual current loop is analyzed,and it is concluded that the ratio of residual current and unbalanced current mutation vectors changes with the grounding faults but not with the load switching.Then,the mutation of the fault current is calculated based on the stabilization of the neutral line impedance and the system grounding impedance and leakage faults are detected with the criterion that the calculated fault current exceeds certain threshold.Simulations and tests prove that the proposed method can effectively distinguish the residual current variation caused by load switching and leakage fault,and realize the leakage fault detection on the condition of large inherent residual current.The detection sensitivity in single-branch and multi-branch systems is 70 and 150 m A,respectively,satisfying the sensitivity requirements for the multi-level leakage protection of TN-C-S systems.