Research On Risk Assessment Method Of Power Grid Considering Time-varying Failure Rate Of Overhead Lines

With the fact that most wind resource-intensive areas are far away from load centers in China,Ultra high voltage DC transmission technology is widely used in longdistance transmission to promote the consumption of wind energy.However,the uncertainty of wind energy and the random contingency of overhead lines pose a great threat to system security.Therefore,a method for reasonably quantifying system operation risks is needed.This study will start with modeling the time-varying failure rate of overhead lines,using the collected equipment micro-meteorology and operating data to get the failure probability in real time.Then,a wind power output scenario fluctuation model and a DC line multi-state fault model will be constructed,and the improved scattered sampling Monte Carlo method is used to sample the system risk scenario set.Finally,multi-dimensional risk index calculations are performed on a scene-by-scenario basis to achieve a reasonable quantification of risk.Firstly,the outage of overhead-lines seriously affects the stability of power system operation,so the establishment of overhead-lines' time-varying failure rate model considering internal and external factors is the key to the risk assessment of power system operation.Based on the failure mechanism of overhead lines,this paper proposes the Multi-Drive-PHM(MDPHM).This model is based on the Proportional Hazard Model.The model's baseline hazard function adopts aging failure model and the covariates of connected function include the equipment health status,load rate and weather conditions,and the correlations between these covariates and the failure rate are calculated through the testing statistical hypotheses.The Levenberg-Marquardt method is used to estimate the parameters of this model in the final step.The case study quantitatively shows the impact of different factors on the overhead-line failure rate,verifying the validity of this model.Secondly,in order to quantify the operational risk of hybrid AC/DC system with large-scale wind power integration,this paper proposes a risk assessment method based on improved scattered sampling Monte Carlo method(ISS-MC).Firstly,according to the number of twelve-pulse bridges blocked after fault,a five-state UHVDC model is proposed.And segmentation discretization method is adapted to construct wind power fluctuation prediction scenarios.Secondly,the sampling process of multi-state components with scattered sampling method is presented,and a risk assessment process is established based on ISS-MC.Finally,a relatively complete risk indicator system is proposed from the aspects of fault state,economic loss and structual strengh.Besides,a comprehensive risk indicator is constructed with entropy weighting method.Some risk indicators are calculated using AC power flow and AC optimal power flow to improve the accuracy of assessment results.Simulation on modified IEEE-RTS79 system validates effectiveness of the proposed model and method.This research provides reference for arrangement of system operation modes.Finally,based on the above research and the actual needs of power grid operators,a risk assessment and management system for the entire process of regional power grid operation is developed.The main functional logic,the entire process risk assessment and management mechanism and the related software development technologies are detailed described in this paper.The system has been deployed in a regional power grid,which achieves refined risk check of maintenance plan,operation plan and real-time operating status in the operation process of regional power grid.In addition,a variety of control methods including load transfer path are provided for high-risk scenarios,which realizes the closed-loop of risk dispatching and enhances the breadth and depth of power grid security risk prevention and control.