Research On On-line Monitoring Vacuum For Vacuum Circuit Breaker

With the spring up of medium and low voltage switchgear oil-free wave, the application of vacuum circuit breaker is more and more widely. Vacuum circuit breaker is a switch equipment in which vacuum is used as insulation interrupter with the advantages of small volume, high reliability, long service life and so on. To ensure the safe and stable operation of vacuum circuit breaker high vacuum must be guaranteed. Therefore, the realization of on-line monitoring of vacuum degree has become a problem which need to be solved.This paper firstly introduces the development of vacuum circuit breaker and the common methods of vacuum monitoring. Off-line test method is the conventional test methods. This technique has been widely used because of its technical maturity and can be realized easily. But this method need power-off operation and regular maintenance, which result in a tremendous waste of human and material resources. The rise of on-line monitoring technology can solve this problem. At present, scholars have done a lot of researches for the on-line monitoring of vacuum degree. The commonly used methods are coupling capacitance method, photoelectric conversion method, HF pulse current method and so on. But the measuring accuracy is limited.This paper analyzes the theoretical basis of coupling capacitance. A coupling capacitance probe was designed and a innovative use of differential input circuit to inhibition the interference from system voltage fluctuation. This design improves the measurement accuracy. The paper goes on and designs the hardware circuit to gather the partial pressure signal of coupling capacitance and system voltage. Through signal handling unit, the real change curve of the vacuum interrupter can be achieved. This paper also set up an experimental device of online monitoring system. The lower computer AVR MCU communicates with host computer by RS-232 standard. By using host computer, display and storage is realized.The system is based on the AVR MCU. Select C language as programming language. Matlab is used to achieve the fitting curve and C++used to write an upper computer interface. Thus a complete and strong applicability of on-line monitoring vacuum system is realized.The experimental results and the real data are contrasted in this paper to verify the reliability and sensitivity of the system. Experiments have shown that the on-line monitoring vacuum can effectively realize the measurement of the vacuum degree and alarm of the inflection point.