Maintenance scheduling for HV cable based on the delay-time concept

A delay-time concept based approach to scheduling of HV cable inspection and maintenance is proposed in this paper. Based on the delay-time concept, the progress of cable failure can be regarded as a two-stage process, one being a stochastic process of defects arrival which can be introduced by Poisson distribution and the other being a delay-time interval from defect to failure which can be expressed by exponential distribution. According to the service duration of a cable and its historical periodicity of inspection, the use of a statistical model representing cable failures for scheduling maintenance activities is established. Within the delay-time interval, a defect can be identified and eliminated prior to it turning into failure through daily inspection, testing and maintenance. Cable circuits within different service age are considered individually due to their characteristics of failure progress versus service age vary with individuals. Then the maintenance activities can be optimally scheduled by setting the objective functions as the minimal maintenance cost, where the overall cost of HV cable maintenance is considered as including the potential failure loss and daily inspection and testing cost. In this way, maintenance Scheduling can be automatically formulated and updated whenever failure data changes. The optimal approach have been applied to test against thousands of cable circuits in southern China. The economic expenditure could be reduced by 37.46%, compared with the total cost before optimization, because the periodicity of inspection has been optimized to fit within the delay-time interval from defect to failure.