| The reliability and safety of DC system will directly effect the reliability and safety of electric power system. The structure and the equivalent circuit of DC system are introduced and several types of ground fault in DC system are described and analyzed in this paper.This article is based on the several faults of circuit breaker tripped during power transmission from the Jinqiao thermal power plant in2006. For this case, this paper analyzes the reason of faults and confirms these entire phenomena are correlated with DC system. Due to ground capacitance of the bus in DC system and capacity effect in long cable, the failure at the end of the DC system or single-point grounding fault may happen,which could result in protection malfunction. So this paper makes a detailed analysis which confirm that the frequent malfunction of Jinqiao power plant switch is caused by DC system fault. This paper summarizes the reasons and types of DC system faults and the power plant has been modified in the end. As a precaution, for the above theoretical research and analysis, the Jinqiao thermal power plant develop four measures and simulate the DC bus grounding and AC system into DC system.In this paper, thorough studies that have been made on the reasons and the types of fault in DC system, the effect of the distributed capacitor with long cable on relaying protection in power plant and substation, the characteristics of forming a ring network after the phenomenon of two or more sets of DC system of electrical connection are analyzed. At home and abroad DC system grounding fault detection principles and pros and cons are developed. This work makes preparation for the design for DC system and ensures the DC system run safely and stably. Finally this article summarizes the work, and puts forward the following work and expectations. |
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