International Congress of Electrical Distribution IMPACT OF SYSTEM RELATED FACTORS ON THE DISTRIBUTION RELIABILITY, A STATISTICAL ANALYSIS OF TWO SWEDISH DISTRIBUTION GRIDS

Regulatory regimes that put focus on performance rather than looking at the actual costs of the distribution system operators (DSOs) create strong cost-cutting incentives, and to avoid system reliability deterioration the quality of supply is most often a feature in the performance yardstick. This has raised the stakes due to quality and consequently increased the interest that the DSOs have regarding their quality of supply. As in many European countries, this is the scenario in Sweden. As a tool to value the DSOs’ performance the Swedish regulator uses the Network Performance Assessment Model (NPAM), which is a reference network model. Since the direct link between the DSOs ’ costs and income is weak, the costcutting incentives are rather strong, thus the quality of supply features within the regulation makes a significant contribution in the performance yardstick. This have resulted in that now the distribution system operators can be penalized due to poor quality of supply, which means that greater effort is now put into analysing and evaluation their quality performance. The underlying project is result of this development. This paper presents some of the main conclusions of a project conducted during 2005, where comprehensive outage statistics, covering tree years from two separate distribution grids, have been gathered, organized and analyzed. The purpose has been to analyse the connection certain system related factors and the interruptions that occur in the distribution systems. The analyses are categorized according to customer related and interruption related factors. 2