Influence Analysis of Distributed Capacitance on Tripping Relay and Relevant Control Measures

Eighteen counter measures make the corresponding requirements of relay action power and action voltage from the view of design, but if DC grounding fault or AC intruding happen, while distribution capacitance of control cables exceeds the critical value, the export relay may malfunction. In this paper, the on-line monitoring system of distributed capacitance of control cables is built to realize the early warning of the risk: firstly, the low-frequency alternating current signal is injected into the DC system, then the AC current value is measured and the distributed capacitance is calculated, finally the measured value is compared with the critical value. In order to measure the distributed capacitance accurately and steadily, a small AC and DC measurement CT is designed based on magnetic saturation principle and flux induction principle. Based on constant resistance mode of DC electronic load, a voltage equalization module is designed to balance DC Bus voltage. The scheme relies on the reliable microcomputer insulating monitor and portable detector to further develop, with high economy and safety. The site is running well good, to avoid the adverse effects of distributed capacitance of the cable on export relay.