Evaluation of alternative MV distrubution network plans from reliability point of view

There is an increasing need for electric utilities to be more effective and cost conscious. They are enforced to control trustworthily total lifetime costs caused by their network components without jeopardizing the reliability and security of the network. New distribution planning methods and procedures are needed in order to meet the expectations and performance targets of regulators, company owners and customers. One of the most challenging tasks for electrical utilities is the consideration of reliability as a part of long term planning of the network. An advanced IT-solution has been developed at Tampere University of Technology (TUT) in order to provide reliability analysis as a part of the network planning process. The software implementation and the developed models for reliability analysis are presented briefly in this paper. The focus of the paper deals with studies in which alternative plans for a new distribution network are generated and compared with the developed application. For each plan the total lifetime costs are calculated, including reliability costs. The optimal plan depends on the selection of reliability optimization criteria: the reliability costs may consist only of direct utility costs, but they can also include customer interruption costs and even the costs of voltage dips. The paper presents and evaluates the results of example studies and discusses the correlation between the utility strategy and optimal network structure.