Investigating the benefit of conditionmeasurements for critical componentsin power transmission systems

Abstract: This master thesis project has been conducted as a collaboration between Svenska Kraftnät and the Royal Institute of Technology.   High demands are being put on all components in a transmission system to be available for operation, making the allowed component down-time the limiting factor in the maintenance budget for Svenska Kraftnät and other transmission system operators. By conducting condition measurements that can be performed on-line, excessive down-times could be avoided in a step towards an as efficient maintenance strategy as possible. The approach of this thesis work has been to perform a case study for a population of transmission grid circuit breakers, creating a model of the CBs’ lifetime which has then been simulated with the aim of studying the benefit of periodic on-line condition measurements for power system components. The main potential benefit examined is the decrease in total downtime for the component population, in relation to the respective components’ criticality. The conclusions of this thesis project are summarized below. -Replacing the periodic off-line preventive maintenance with on-line condition measurements for the most critical circuit breakers in a power transmission system, significantly diminishes the weighted overall down-time for all circuit breakers in the system. - It is most preferable to use frequent intervals for condition measurements for a large part of the circuit breaker population. - A maintenance strategy based on condition measurements is best motivated in cases where the randomness of circuit breaker condition deterioration is high, the failure rate is high, or condition measurements have low uncertainty, and least motivated in cases where the conditions are the opposite. - Severe transient effects in average age of the component population may appear in response to any changes in maintenance strategy (or the lack of it), having a harsh impact for power system owners.