Reliability indices estimation of unstationary distribution networks

The paper presents an efficient and overall analytical approach towards the prognosis of reliability indices in the process of development of medium voltage city distribution networks. The presented model gives possibility for estimation of duration of the interruption of supply of the load points in question, due to unexpected failure at some, arbitrarily chosen, element of radial distributive network. Repair crew movement during searching for the faulted cable section is modeled, in order to estimate time needed for isolation and renewal of supply of load points. The differences in strategies of searching and isolating of the faulted section are also taken into consideration. The reliability analysis is possible in the case that the dispatcher and the crew for maintenance search for the section by use of halving method or by the method of measuring the resistance of isolation using megaommeter. Application of the model and developed computer program is illustrated on the example of the real network of the city of Novi Sad. Some feeders are analyzed as unstationary elements which during the planned period change the configuration, number of load points, load and unit outage costs. The change of configuration is manifested by connection of new MV/LV substations between the existing ones, or by prolongation of lines. The change of the configuration of open loop depending on link arrangement is considered. The results give a real reliability picture of the present but also of the future MV network. In addition, data thus obtained can be used as basic ones for the estimation of benefits in cost-benefit analyses.