Abstract
Regular maintenance inspection and testing is essential in extending cable life and reducing failure probability. This can be achieved by improving the conduit conditions and taking corrective actions on faulty cable components and accessories. Regulators and corporate governance among power utilities require the implementation of risk-based approaches to asset management. However, practitioners lack sufficient historical event data and knowledge that allow them to determine the failure probability of individual cable components, which is an essential component for risk assessment, due to that the high voltage (HV) cable population are relatively young, and many have not yet reached the end of their design life. This paper presents a novel holistic approach to allow the risk based maintenance strategy to be conveniently implemented for the cable conduit, cable terminations, joints, main bodies and the earthing systems separately for each cable circuit. Contributions include: (i) a failure frequency model which accounts for every past failure record of individual cable circuit components to approximate the probability of failure. This, when multiplying with the cable importance or failure consequence, yields the risk level of an individual cable component or a cable circuit; and (ii) a method of optimally scheduling the maintenance activities by setting the objective functions as the minimal cable system risk. The benefit of the simple failure frequency model has the advantage of not having to depend on human intervention and it does not need a large sample to generate valid results, as is the case with other statistical methods. Results of applying the proposed maintenance scheduling model to 21 selected High Voltage (HV) cable circuits show that the average risk can be significantly reduced while continuing with the same number of inspections and test operations.
Highlights
High Voltage (HV) and Medium Voltage (MV) power cables, which form the backbones of the urban electrical networks worldwide, are expensive to maintain and to replace
The life of a cable is dictated by insulation degradation due to electrical and thermal stresses [3], and the failure probability of a cable or cable population should obey the curve shown in Fig. 1(a), where the likelihood of failure is relatively low between the date of commissioning and a certain point in time when age related insulation degradation causes the failure probability to increase exponentially
This paper proposed a holistic approach to modelling of failure probability and scheduling of maintenance activities, whereby cable circuits are considered as being divided into component types, i.e. cable conduit, terminations, joints, cable bodies and earthing systems
Summary
High Voltage (HV) and Medium Voltage (MV) power cables, which form the backbones of the urban electrical networks worldwide, are expensive to maintain and to replace. There is still a gap between the maintenance management aim and the practice, as practitioners lack sufficient historical event data and knowledge that allows them to assess the failure probability of individual cable components This is due to that the high voltage (HV) cable population are relatively young, and have not yet reached the end of their design life of 30-40 years for polymeric XLPE cables, and 60-70 years for paper insulated PILC cables. Conduit condition data will be essential for evaluating the failure probability of cable bodies and joints, this assessment is an important part of cable circuit inspection and maintenance
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