روش احتمالاتی برای برنامه ریزی فعالیت های نگهداری اجزای فرعی

This paper suggests a probabilistic method for the calculation of operation cost throughout a planning period and availability evaluation of substation components, in connection with planned maintenance activities. This method is conceived to provide lower operation cost, consisting of failure repair cost and maintenance cost, and higher availability of substation components. The method identifies minor and major failures. It is assumed that each component has two independent, competing failure modes: wear-out failure mode, modelled by a two-parameter Weibull distribution, and a chance failure mode, characterized by an exponential distribution. The application of the method suggested is demonstrated for a 145 kV air-blast circuit-breaker. By applying the method, influence of condition monitoring systems application on operation cost is evaluated. Also, because of comparison, expected operation cost in case of time-based maintenance performing is calculated.

Operation cost during exploitation period of substation consists of preventive maintenance cost and major failure repair cost. The purpose of traditional, time-based, preventive maintenance is to extend substation component lifetime, i.e. the mean time between failures. Time-based preventive maintenance is performed after TBM time units of continuing operation without failure. If a failure occurs prior to TBM, then repair is performed at the moment of failure. In either case, we assume the component is returned to “as good as new” condition. Practically, the expected operation cost during period of TBM time units equals Many electric power utilities have planned, up to now, preventive maintenance activities based upon their experience or manufacturers' recommendations. Too frequent performing of maintenance demand unnecessary expenditures. On the other side, too little maintenance may have very costly consequences (high cost of failure repair and the loss of revenue). The aim of this paper is to propose a model enabling the evaluation of frequency of preventive maintenance performing, in order either to minimise the operation cost or to maximise component availability. Due to proper estimation whether certain plans are acceptable or not, it is worth noting two facts:)> • It is necessary to have a precise operation data for a certain type of substation component (reliability data, cost of preventive maintenance and cost of failure repair); • Since the substation component consists of several functional parts (HV-parts, electrical control and auxiliary circuits, operating mechanism, etc.), it is necessary to perform an analysis for each functional part and, after that, based on the results, select the most favourable schedule of maintenance activities. In the following section, a cost model and a limiting availability model for a repairable component are formulated.

A model is suggested for the calculation of component availability and calculation of the expected operation cost throughout a period between scheduled maintenance activities. The model is based on the fundamental assumptions of reliability theory and enabling simple performing of analysis of different concepts in order to determine the most favourable plan of substation components maintenance. Analyses can be performed in order to find an optimal preventive maintenance period that either minimises cost per unit time or maximises limiting availability. The most interesting data about efficiency of condition monitoring systems are quoted. The model assumed that the following values are known or may be estimated from exploitation data: cost of inspection, cost of major failure repair, cost of minor and major deterioration repair, expected major failure repair time and expected preventive maintenance action time. Application of model is demonstrated for a 145 kV air-blast circuit-breaker. Comparisons of Fig. 3 and Fig. 7 indicate the obvious beneficial effects of the suggested model.