Risk Assessment Of Relay Protection Considering Uncertainty

The development of power system has brought great benefits to people's life and production,and also put forward new challenges to the safe and stable operation of the power system.Relay protection is the first line of defense to ensure the safe and stable operation of the power system,and its incorrect action could seriously affect the reliability of power supply.Therefore,assessing the risk of the relay protection equipment,cutting off the risk transmission chain and finding the weak links have a decisive significance to ensure the reliable and economical operation of the power system.Firstly,a state evaluation system of generalized evidence theory is presented,which is based on confidence coefficient.The normal cloud model is utilized to calculate the membership degree.And the improved fuzzy analytic hierarchy process combined with the local penalty-incentive state variable weight function is adopted to calculate the weight of the evaluation index.So the fuzzy evaluation is calculated,and the result is taken as the basic probability distribution of the evidence.Finally,a case study points out that the evaluation result based on the generalized evidence theory is reasonable and the data fusion speed is relatively fast,which provides a new way of thinking for the state evaluation of relay protection in the background of large data.Secondly,on the basis of the evaluation of equipment status,a generalized proportional hazard model is established.The parameters are estimated by the means of Maximum likelihood estimation.In the meantime,the nonlinear equation is figured out by the adaptive homotopy algorithm.Three cases demonstrate that adaptive homotopy algorithm is better than Newton homotopy algorithm,regarding of the calculation speed and convergence;the generalized proportional hazard model could reflect the real time fault rate of the equipment,and it provides sound theoretical basis for the selection of equipment maintenance types.Meanwhile,a risk assessment system considering transmission line and line protection is put forward.The correctness and efficiency of the theory is verified through the calculation and simulation results of the WSCC-9,which considers the fault of the protection.Thirdly,a failure rate prediction model based on double condition single rule cloud reasoning language is proposed to excavate the relationship between the health index,human failure rate and failure rate.The results show that the failure rate model integrating the human factors is more close to the actual operation condition of the equipment.In addition,the human factors are not negligible.Additionally,the analysis of practical data indicates that the prediction results of failure rate based on the double condition single rule are more consistent with the statistical regularities than multivariate regressive method.Finally,the soft layer model is used to establish the risk assessment model of relay protection to solve the uncertainty in the process of the risk assessment.First of all,according to the definition of risk,it points out the factors that influence risk.Then,the state evaluation model is used to calculate the accident probability and the assignment method is adopted to calculate the loss.In the meantime,the fuzzy information granulation algorithm is applied to process the data of accident probability and accident loss.Besides,the risks of multiple regions are sorted on the basis of the fuzzy ranking method,which can provide theoretical basis for risk managers to make right decision.Last but not least,the actual data in a certain area could validate the correctness and effectiveness of the fuzzy information granulation algorithm for the relay protection risk assessment.