Cable Fault Differential Current Protection Method Based on Dual Current Transformer

Abstract

随着城市规模不断扩大，配电网电缆化占比越来越高，电缆故障发生率也随之提高。由于单相接地故障形式多样，受过渡电阻、中性点接地方式、电流互感器不平衡等因素影响较大，故障检测与排查难度较大，电缆沟爆炸等事故多发，严重影响了供电的可靠性。因此，有必要对配电网电缆接地故障保护方法进行研究与改进。本文对中性点不接地、消弧线圈接地、小电阻接地配电网电缆单相接地故障零序电流分布特征进行了分析，在此基础上，计及过渡电阻的影响和电流互感器误差影响，提出了一种基于双电流互感器的电缆故障差动保护方法。通过在电缆馈线两端分别安装两组不同量程的电流互感器，一定程度上减小了电流互感器误差，提高了差动保护的灵敏度。仿真结果表明，相比于传统单一互感器，基于双电流互感器的电缆故障差动保护具有更高的抗过渡电阻能力和灵敏度。 As the urban construction process accelerates, the proportion of cable distribution in distribution networks is increasing, and the incidence of cable failures is also increasing. Due to the various forms of single-phase grounding faults, fault protection is greatly affected by factors such as transi-tion resistance, neutral grounding mode and current transformer imbalance. Fault troubleshooting is difficult, and cable trench explosions and other accidents occur frequently, which seriously af-fects the reliability of power supply. Therefore, it is necessary to study and improve the grounding fault protection method for distribution network. In this paper, the zero-sequence current distri-bution characteristics of single-phase grounding faults are analyzed in distribution network with neutral point ungrounded, arc-suppression coil grounded and small-resistance grounded. On this basis, considering the influence of transition resistance and the current transformer error, a cable fault differential current protection method based on dual current transformer is proposed. By in-stalling two sets of current transformers with different ranges at the two ends of the cable, the cur-rent transformer error is reduced to some extent, and the sensitivity of the differential protection is improved. The simulation results show that compared with the traditional single transformer, the cable fault differential current protection based on dual current transformer has higher re-sistance to transition resistance and sensitivity.