SUMMARY
Reduction of failure rates and applying effective faultmanagement can be affected in improvement of reliabilityindices in distribution systems. One of the ways to improvingthe reliability of distribution networks in fault managementprocedure is installing Fault Indicators (FIs) in overheadprimary networks. FIs allow operators to quickly identify thelocation of a fault on overhead lines feeders. FIs can reducefault localization and therefore reduction in outage durationand outage cost. In this paper, modelling of FIs in reliabilityassessment and computing of related indices such as SAIFI,SAIDI, CAIFI is introduced. Using model development andcase studies it is discussed and shown that location andnumbers of FIs effect in distribution reliability indices.
Keywords: Distribution Systems, Fault Indicators, Reliability,Modelling.
1. INTRODUCTION
The basic function of an electric power system is to supplycustomer with acceptable degree of continuity and quality.Analysis of the customer failure statistics has shown thatbecause radial configuration of feeders and high failure ratesin equipments and feeder sections, distribution systems makethe greatest contribution to the unavailability of power supplyto customers [1].There are only two main ways to improve the reliability ofpower distribution networks. The first one is to reduce thefrequency of customers' interruptions and the second is toreduce the outage duration once the failure occurs [2- 4].One of the ways to improving the reliability of distributionnetworks in fault management procedure is installing FIs inoverhead primary networks. FIs allow operators to quicklyidentify the location of a fault on overhead lines feeders.Operators can then isolate the faulted section and beginnecessary repairs and switching actions in minimum time. FIscan reduce fault localization and therefore reduction in outageduration and outage cost. They can be used in existingnetwork with minimum cost and installing time. Also it can beused in systems with and also without distribution automationsystems. However if they are equipped with sending signals tocontrol center, the fault can be localized very quickly usingGIS systems.One of the tasks associated with the using of such devices isto evaluate quantitatively the effect of FIs on reliability ofdistribution systems for developing an effective method foroptimal determining of numbers and lactations of FIs.In the past years, reliability modelling and assessment ofdistribution systems have received considerable attention, andthere are a number of publication dealing with the theoricaldevelopment and modelling methods.In order to give more realistic modelling the effect of the FIs,the features associated with the fault management strategyneed to be included in the reliability assessment.In this paper, modeling of FIs in reliability assessment andcomputing of related indices such as SAIFI, SAIDI, CAIFI,…is introduced [5]. It performs a number of sensitivity analysesof system reliability. Using model development and casestudies it is discussed and shown that location and numbers ofFIs effect in distribution reliability indices.
2. MODELLING AND EVALUATION TECHNIQUE
Following a fault occurrence on a feeder, faulted section ofthe network is identified and isolated, then the service isrestored to un-faulted feeder sections and faulted section isrepaired [6, 7]. This process is illustrated in Figure


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