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Wu J.-W.,Beihang University | Xue L.-J.,Beihang University | Zhang S.-B.,Zhuhai Keli Electrical Group Ltd. | Lian S.-J.,Zhuhai Keli Electrical Group Ltd.
Gaoya Dianqi/High Voltage Apparatus

For the common functional characteristic of microcomputer-based protection and online monitoring for medium voltage distribution circuit breaker, a synthetic monitoring device with the two functions is designed based on dual-CPU structure. This device has the functions of phase-sequence over-current protection, zero-sequence current protection, phase-lack fault and wire-breakage fault detection, and fault recording. It implements the monitoring of the circuit breaker's mechanical features, electrical endurance, secondary circuit status, ambient humidity, and temperature of conductive connections through collection, storage and process of needed signals, and realizes field display of fault information and the circuit breaker status via large-screen LCD. μC/OS-II embedded operating system is used in the software design. The stability, real-time performance, reliability and maintainability of the device are enhanced through reasonable division of tasks and priority assignment. Experimental results show that the precision of state parameters is measured less than 2%, demonstrating the device is reliable. Source

Hu H.,Beihang University | Wu J.,Beihang University | Zhang L.,Zhuhai Keli Electrical Group Ltd. | Lian S.,Zhuhai Keli Electrical Group Ltd.
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society

The total error of the system can be reduced effectively by a reasonable distribution proportion of the error sources when the electrical signal measurement system was designed. The effect of the signal frequency change, the signal measurement range, the transducer precision, the A/D precision, and the data shifting were analyzed in this paper. Moreover, an integrated measurement error of electrical signals RMS(root-mean-square) mathematical model was deduced, and the error model was verified by the calculation results. Meanwhile, the error model was applied to the relay protection prototype. 1A low current with the measurement error low then 0.4% and 5A (or above) current with the measurement error low then 0.2% were achieved in this paper. The model of error calculation provides the basis for the best design of Error distribution on measurement system. Source

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