Probabilistic method for planning of maintenance activities of substation components Vladica Mijailovic Technical Faculty, University of Kragujevac, Cacak, Yugoslavia Received 19 March 2002; received in revised form 27 May 2002; accepted 12 June 2002 Abstract 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. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Probabilistic method; Substation components; Minor and major failures 1. Introduction Operation cost during exploitation period of substa- tion 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 pre- ventive maintenance is performed after T BM time units of continuing operation without failure. If a failure occurs prior to T BM , 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 T BM time units equals C TBM (T BM ) e l MF T BM C pm (1 e l MF T BM )C MF : (1) 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 unneces- sary expenditures. On the other side, too little main- tenance 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. Electric Power Systems Research 64 (2003) 53 /58 www.elsevier.com/locate/epsr 0378-7796/02/$ - see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0378-7796(02)00148-7