Assessment of electricity distribution reliability - interruption statistics, reliability worth, and applications in network planning and distribution business regulation

Abstract

In modern information society requirements and expectations associated with the continuity of power supply have become increasingly important. Electricity is not a luxury article anymore like it was a few decades ago, but it has become a necessity and a part of our everyday life. Even short interruptions can be harmful when the amount of computers, programmable logics etc. in industry and as well in households have increased rapidly. Large blackouts around the world have also aroused the customers’ interest in electricity distribution and the reliability of distribution networks. The reliability of supply is again of great interest.

This thesis introduces new methods for reporting interruption data. This includes the development of interruption statistics and the methods of gathering interruption data while taking into account the needs of different interest groups, i.e. the DSO, its customers and the regulator.

Reliability worth and interruption costs are becoming widely used in the regulation of distribution companies. The main objective of the regulation is to increase the cost-efficiency in the electricity network businesses for the benefit of the customers, while still maintaining acceptable levels of supply reliability. In the distribution system operators operating environment where there is an increased demand for cost-efficiency, the sufficient level of reliability can be ensured with continuity of supply regulation, and with the use of interruption costs in regulation.

This thesis presents methods used to compose reliability worth estimates and to eliminate strategic responses from customer survey data. The regulation model used in Finland is outlined from the reliability of supply point of view. The results of the reliability worth study show that there has been a significant increase in the reliability worth estimates during the past ten years, which is also reflected to customer expectations on supply reliability.

For distribution network companies, the reliability-based network analysis can offer an excellent tool for focusing network investments in the most critical areas in the network, and thus use the assets in the best way to increase the level of reliability. Interruption statistics, in turn, produce valuable source information for reliability analysis.

Reliability-based network analysis is presented in this thesis with the help of example calculations in the cases where different reliability parameters are examined. The results show the total costs (divided into operational, investment and interruption costs) during the technical lifetime of the network. As customer expectations on reliability worth and economical significance of interruption costs increase, more reliable, but also more expensive, network development alternatives become more attractive.