| DC system in substation and power plant supplies power for protecting, measuring and controlling equipments. The health of DC system is critical to safe and reliable operation of power system. Grounding fault is the most common failure in the DC system. It presents serious danger on system safety as a new grounding point may cause short circuit fault or relay mal-operation. The research of online insulation equipment aims at this.The author analyses several familiar detecting methods of DC power supply, concretely expounds their advantages and shortcomings. Based on this, Ping-Pang method is proposed as the principle of this equipment, and the grounding fault monitoring system is designed. Furthermore, the author explains the researching method from two aspects, software and hardware included.The device adopts single-chip produced by WINBOND as the core controller which responsible for the sampling the analog signal and calculating the insulation resistance, adopts CPLD produced by ALTERA to accomplish address allocation, peripheral chips selection and keyboard decoding, adopts digital potentiometer and instrumentation amplify to achieve wide-scope measurement. The author describes the structure and elements of this device, and presents particular discussion about hardware design, including interface of single-chip and CPLD, sampling circuit, amplify circuit, isolation circuit, communicating circuit, display circuit, and finishes software design and experiment result analysis is also given.
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