HV Circuit Breaker State Assessment Based On Cloud Model And Gray-fuzzy Comprehensive Evaluation

With the development of society and economy, the size of grid further expands to meet the needs of production and life, and its security and stability will face more severe test. As an important part of the power system, the operating status of power equipment will directly affect electricity operation of the system. As the core switchgear of the power system, the HV circuit breaker plays a dual role of protection and control. The protective effect mainly embodies in the aspect when the power lines or equipment go wrong, the circuit breaker removes the fault rapidly, with the cooperation of relay protection device, and ensure the normal operation of system non-fault area. The control effect mainly embodies in the aspect when the system runs normally, the circuit breaker inputs or removes the part of the electrical equipment or lines to meet the needs of power system operation. The HV circuit breaker will bear the impact of electricity, heat, environment, and other factor during operation, so the performance will be a certain degree of deterioration,which results in a potential threat to the stable operation of the power system. If the development of deterioration, being to a certain extent, will become to faults that will have a direct impact on the operation of the power system. If the fault is slight, leading to the power outages of some users, or causing damage to parts of electrical equipment. In contrast, the fault will cause a chain reaction leading to the system collapse, which will have a significant impact on people’s production and life. Therefore, accurate and efficient HV circuit breaker condition assessment is of great significance for the further development of the maintenance program to ensure the safe and stable operation of the power system.HV circuit breaker state assessment system is a complex multi-factor evaluation system, whose assessment factors being fuzzy, gray and randomness. Based on the research and summarize of predecessors’ work, this paper applies the cloud model theory and gray-fuzzy comprehensive evaluation to the HV circuit breaker state assessment, and propose a new thought on HV circuit breaker state assessment, which considers the HV circuit breaker state assessment factors of fuzzy, gray and randomness, making assessment results more effective and reliable.Firstly, based on the analysis of HV circuit breakers pilot projects and associated operating parameters, the paper combing with the relevant principles of system modeling selects a representative index, then establishes a multi-level assessment factors set. Secondly, considering the amount of computation and assessment precision, divides reasonably the operational status levels. Then, using the improved Analytic Hierarchy Process determines the fuzzy part of the weight set. While, the gray part of the weight set is determined with the redundancy degree of information and the experiences of experts. Its fuzzy part indicates the relative importance of the assessment factors on the same level. The respective gray part expresses the credibility of the fuzzy part determination. Finally, combining quantitative analysis and qualitative analysis method, using the membership degree to describe the fuzzy affiliation between the assessment factors and each state grade, and with the pixel gray scale to describe the incredibility of the fuzzy relation, then establishes the gray fuzzy discrimination matrix. For quantitative indicators, its membership degree is determined with the cloud model, for qualitative indicators, its membership is determined by fuzzy statistical test. In summary, the operational state of HV circuit breaker is assessed comprehensively, and the final assessment result is determined with the combining method of the inner product method and the maximum membership degree principle. The practical calculation example shows that the proposed model can objectively and effectively assess the state of HV circuit breakers.