Mechanical Condition Assessment of High Voltage Circuit Breakers Based on Improved Dempster-Shafer Theory

Among all kinds of faults that affect the operation reliability of high-voltage circuit breakers, mechanical faults account for the highest proportion. Therefore, it's necessary and urgent to find an effective way for mechanical condition assessment. In this paper, the vibration signal, opening/closing coil current and stroke-time curve are selected to evaluate the mechanical condition of high voltage circuit breakers in order to overcome the shortcomings of single signal diagnosis. Dempster-Shafer evidence theory (DST), as a method of reasoning for dealing with uncertainty, has been widely used in information fusion. Therefore, this paper chooses DST to carry out multi-signal fusion and comprehensively evaluates the running status of the circuit breaker. However, in order to overcome the defects of DST in dealing with conflict evidence, this paper proposes an improved DST. Firstly, various signals are combined to assess the accuracy of the allocation of uncertain information and the evidences are constructed. Secondly, the evidences are corrected based on the similarity coefficient and similarity matrix between the evidences, and then the evidence fusion is performed. Thirdly, based on the evidence distance between the new evidences and the original evidences, the best original evidence is selected and uncertain information of the merged evidence is redistributed. Finally, mechanical condition of the high voltage circuit breaker is determined. Identification experiments are carried out to demonstrate the effectiveness and feasibility of this method, avoiding the misjudgment due to the abnormality of single signal.