Asset Management Strategies Of Circuit Breakers Considering Ageing Failures And System Risk

Circuit breaker is the cornerstone for power system operation,which is expensive and widely used in the power supply companies for cutting the fault current,isolating the fault area.The power failure caused by ageing circuit breakers become increasely prominent.How to effectively manage the ageing circuit breakers become a challenging problem facing by the power supply companies all over the world.However,the traditional asset management modes based on deterministic principle and engineer experience that ignore the ageing impact of equipment failures on system risk and lack of the analysis of condition monitoring information will lead to the waste of maintenance resources and the lacking of efficient maintenance for equipment.Therefore,this thesis studied the ageing asset management strategy and proposed the idea of combining equipment ageing condition and system risk evaluation.With such asset management strategy,the ageing failures model of circuit breakers based on the condition monitoring and system risk can be considered in a unified sense.To incorporate the ageing failures in the reliability model for circuit breakers,this thesis proposes Wear Index and the ageing failure model based on condition monitoring.By analyzing the role of the main component in circuit breaker,this thesis presents ageing failure model for the main component of circuit breakers according to statistical analysis of historical data.Furthermore,the Wear Index is presented to reflect the ageing condition for the circuit breakers.The ageing failure model based on condition monitoring compensates the existing reliability model.The simulation for 637 circuit breakers failures shows the validity of proposed model for ageing equipment.To improve the spare method which does not consider the ageing factor and system risk,the spare strategy for circuit breakers incorporates an ageing failure rate model based on condition monitoring.This strategy determines the spare time and numbers by comparing reliability cost and spare investment.By analyzing 11 circuit breakers in the 110 kV substation,the result shows the spare time and numbers can be effectively determined by balancing the economy,the reliability and the circuit breakers' condition.If the strategy doesn't consider ageing failure,the spare time and numbers will be underestimated.The matrix risk method can determine the the maintenance priority by system importance and health index.To make the full use of this advantage,this thesis replaces the system importance and health index by the system risk and condition monitoring,and then proposes the data-driven model for the maintenance priority.Based on condition monitoring and system risk index,this model cleans the abnormal data by using the unify method and gives the ranking index for the maintenance.By using the Rank Boost algorithm to learn the ranking result under the different index,the optimal ranking with minimum ranking loss is found.By analyzing the maintenance priority for 33 circuit breakers,the result shows the maintenance ranking only based on equipment level or system level may ignore the abnormal equipment and important component in the system.The proposed method can effectively put the urgent circuit breaker in the top list for the maintenance.Inspection is an important step for the maintenance management.This thesis presents the Markov model incorporating the inspection model and failure model based on the maintenance process.Furthermore,an optimization model for analyzing the risk cost in the region is proposed to determine the optimal inspection interval and provides a compensation for the traditional method that adopts the fix inspection interval and ignores the ageing failure.By applying the proposed method in the 2 region,the result shows the ageing failures have an impact to the optimal interval.Therefore it is recommended to determine the optimal inspection interval based on region.If the inspection strategy doesn't consider ageing failures or adopt the fix interval,the inspection cost will increase.