C I R E D 18 th International Conference on Electricity Distribution Turin, 6-9 June 2005 CIRED2005 Session No 1 FAULT INDICATORS EFFECTS ON DISTRIBUTION RELIABILITY INDICES H. FALAGHI M.-R. HAGHIFAM M. R. OSOULI TABRIZI Tarbiat Modarres University – Iran Tarbiat Modarres University – Iran Eastern Azarbayjan falaghi@modares.ac.ir haghifam@modares.ac.ir Electric Power Distribution Co. – Iran SUMMARY Reduction of failure rates and applying effective fault management can be affected in improvement of reliability indices in distribution systems. One of the ways to improving the reliability of distribution networks in fault management procedure is installing Fault Indicators (FIs) in overhead primary networks. FIs allow operators to quickly identify the location of a fault on overhead lines feeders. FIs can reduce fault localization and therefore reduction in outage duration and outage cost. In this paper, modelling of FIs in reliability assessment and computing of related indices such as SAIFI, SAIDI, CAIFI is introduced. Using model development and case studies it is discussed and shown that location and numbers 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 supply customer with acceptable degree of continuity and quality. Analysis of the customer failure statistics has shown that because radial configuration of feeders and high failure rates in equipments and feeder sections, distribution systems make the greatest contribution to the unavailability of power supply to customers [1]. There are only two main ways to improve the reliability of power distribution networks. The first one is to reduce the frequency of customers' interruptions and the second is to reduce the outage duration once the failure occurs [2- 4]. One of the ways to improving the reliability of distribution networks in fault management procedure is installing FIs in overhead primary networks. FIs allow operators to quickly identify the location of a fault on overhead lines feeders. Operators can then isolate the faulted section and begin necessary repairs and switching actions in minimum time. FIs can reduce fault localization and therefore reduction in outage duration and outage cost. They can be used in existing network with minimum cost and installing time. Also it can be used in systems with and also without distribution automation systems. However if they are equipped with sending signals to control center, the fault can be localized very quickly using GIS systems. One of the tasks associated with the using of such devices is to evaluate quantitatively the effect of FIs on reliability of distribution systems for developing an effective method for optimal determining of numbers and lactations of FIs. In the past years, reliability modelling and assessment of distribution systems have received considerable attention, and there are a number of publication dealing with the theorical development and modelling methods. In order to give more realistic modelling the effect of the FIs, the features associated with the fault management strategy need to be included in the reliability assessment. In this paper, modeling of FIs in reliability assessment and computing of related indices such as SAIFI, SAIDI, CAIFI,… is introduced [5]. It performs a number of sensitivity analyses of system reliability. Using model development and case studies it is discussed and shown that location and numbers of FIs effect in distribution reliability indices. 2. MODELLING AND EVALUATION TECHNIQUE Following a fault occurrence on a feeder, faulted section of the network is identified and isolated, then the service is restored to un-faulted feeder sections and faulted section is repaired [6, 7]. This process is illustrated in Figure. 1. Figure 1- Actions after a fault occurrence Existence of FIs can reduce the fault location time and consequently increase the system reliability. For example a typical feeder with a FI is shown in Figure. 2. Figure 2- A Typical distribution system with one FI Assume average fault location time of this feeder without FI is 0.75 hour. With installation of a FI, the fault location time for upstream part of the feeder is: hour 46875 . 0 5 3 5 75 . 0 = + × and for downstream part is: hour 28125 . 0 5 3 3 75 . 0 = + × In general, with installation of n FIs on a distribution feeder, that feeder is divided to n+1 part and fault location time for ith part can be calculated as follow: