Reliability of Electric Utility Distribution Systems: EPRI White Paper

Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication. Applied Decision Analysis LLC (a wholly owned subsidiary of PricewaterhouseCoopers LLP) This report discusses what is known about electric power distribution system reliability and investigates whether there are generally available methods for performing reliability analysis for distribution systems. The theory of the reliability of general systems is well understood. A fundamental issue is whether an appropriate implementation of the theory exists in a form readily usable by distribution system planners and designers. Background EPRI has been developing methods for distribution planning since 1992. At that time, research directed at the concept of distributed resources begun by EPRI, PG&E, and NREL led to further consideration of distribution planning in general. The distribution planning problem is to determine the least-cost expansion plan under load growth uncertainty. Electric utility restructuring and emphasis on competitive performance has increased the importance of the relationship between cost and reliability. Distribution planning must now include reliability/cost tradeoffs explicitly. One of the main questions in the present research is how should reliability considerations be incorporated into distribution systems planning? This is really a multi-part question, comprising such considerations as (a) how is reliability defined for distribution systems; (b) how is reliability valued for distribution systems; (c) how is reliability controlled and maintained in distribution systems; and, (d) what methods exist that measure reliability, predict reliability, or analyze reliability in distribution systems? The present research is aimed at answering these and related questions. Objectives To document what is known about reliability in distribution systems and to determine whether tools exist to perform the required reliability analysis for planning distribution systems. Approach A detailed literature survey, described in the report, created a Reliability Library, a tool intended to support further development of models and methodology. The utility and customer perspectives of reliability were defined and analyzed. The difference is between an equipment focus and a service focus. Approaches to measuring reliability, including indices in common use, were reviewed. There is no single accepted method of measurement. We studied …