基于阻抗修正的反时限过流保护新方案

反时限过流(Inverse-Time Overcurrent, ITOC)保护因其动作时间能跟随故障电流大小变化而变化的特性在中低压配电网中广泛应用。根据反时限过流保护的整定原则,其动作速度易受系统运行方式、故障类型及线路级数影响。另外,分布式电源(DistributedGeneration, DG)的广泛接入也对反时限过电流保护的选择性和速动性带来不利影响。针对上述问题,首先阐述了反时限保护的基本原理及其存在的动作延时过长的问题,并分析了DG接入对反时限过流保护的影响。根据不同位置故障情况下测量阻抗的变化特征,提出了一种基于阻抗修正的反时限过流(Impedance Correction Based Inverse-Time Overcurrent, ICITOC)保护新方案。该方案采用测量阻抗百分比及阻抗修正指数对反时限特性曲线进行修正,可在保证上下级保护配合关系的前提下,最大程度加快保护的动作速度。理论分析和基于PSCAD的仿真结果验证了所提反时限过流保护新方案的正确性及有效性。

A novel impedance correction-based inverse-time overcurrent protection scheme

Inverse-Time Over Current (ITOC) protection is widely used in medium and low voltage distribution networks because its protection operation time varies with the fault current. With ITOC protection, operation speed is easily affected by system operation modes, fault types and line series. In addition, the wide access of Distributed Generation (DG) has a negative impact on the selectivity and speed of ITOC protection. The basic principle of ITOC protection and the problem of long operation delay are expounded, and the impacts of DG on ITOC protection are analyzed. Considering the measured impedance at different fault locations, a novel Impedance Correction based Inverse-Time Over Current (ICITOC) protection scheme is proposed. The percentage of measured impedance and impedance correction index are used to modify the inverse time characteristic curve. This can accelerate the protection operation speed to the greatest extent while the coordination relationship between protections can be guaranteed. Theoretical analysis and PSCAD-based simulation results verify the correctness and effectiveness of the proposed ICITOC protection scheme. This work is supported by National Natural Science Foundation of China (No. 51477090).