Research On Evaluation Method Of Relay Protection State Based On Uncertainty Theory

Relay protection is the first line of defense for the safe and stable operation of the power grid.How to comprehensively,accurately and efficiently master the operation state of protection equipment is of great significance to the safety and stability of the power system,and is also the basic requirement for intelligent operation and maintenance of relay protection.Therefore,it is particularly critical to scientifically and efficiently evaluate the operation state of relay protection.Based on the summary analysis of the evaluation methods of relay protection status,this paper comprehensively considers the large number of uncertainties such as randomness,ambiguity,and dynamic changes in the relay protection evaluation process.By introducing variable fuzzy set theory and set pair analysis theory and cloud model theory,according to the characteristics of real-time monitoring data and historical statistics of relay protection,the corresponding evaluation methods are proposed respectively.The main work contents are as follows:(1)In order to overcome the shortcomings of the classical fuzzy comprehensive evaluation method in describing the dynamic changes of things,the variable fuzzy set theory is introduced,and the related theories and concepts of the variable fuzzy set are introduced,as well as the identification andcomprehensive evaluation models are constructed.(2)Considering the shortcomings of current state assessment methods,such as insufficient utilization of online data,unreasonable weight distribution,unstable evaluation results and difficulty in judgment,a relay protection state assessment method based on set pair analysis and variable fuzzy set coupling is proposed.First,based on equipment condition monitoring information,key indicators were selected to establish a relay protection condition monitoring indicator system.Secondly,entropy method and improved analytic hierarchy process are used to calculate the weight.Moreover,considering that the constant weight often cannot reflect the real situation of the index,the variable weight coefficient is introduced to modify the weight.Then,aiming at the difficulty of constructing the relative difference function in the variable fuzzy evaluation model,a comprehensive evaluation model coupling the improved set pair analysis and the variable fuzzy set is established by using the improved and refined set pair analysis connection function as the relative difference function of the variable fuzzy set model.Through case analysis,the rationality and effectiveness of the evaluation method are verified.(3)In view of the shortage of historical statistical data samples and a lot of randomness and uncertainty in the process of risk classification and assessment,a relay protection risk assessment method based on cloud model is proposed.First of all,the index statistics and hard grading are fuzzified by adopting corresponding distribution functions.Secondly,considering the randomnessfactor,the introduction of the cloud model achieves the "softening" of the risk level and the evaluation matrix is constructed by calculating the evaluation value and the certainty of the level boundary cloud model.Finally,the variable fuzzy comprehensive evaluation model is used to determine the risk level of the protection device.