Selected Indicators of the National Distribution System Dependability

Abstract

The article discusses a significant problem, which is the analysis of the dependability of the national distribution system. The distribution of selected failure rates was analysed in two perspectives: dependability analysis at the local utility company level, and for the distribution power system. In the first part of the paper failure rates are analysed for five domestic utility companies. The second part presents an analysis of the distribution of SAIDI, SAIFI and MAIFI indicators for domestic distribution system operators in 2007–2012. DOI: 10.12736/issn.2300-3022.2013403 Introduction A power system (SEE) is one of the most important engineering systems developed and operated by man. The SEE primary role is reliable delivery of demanded electricity with the required quality to each customer. In market conditions the SEE operation and further development requires the assurance of quality energy supply to consumers in a commercially reasonable manner. The quality of electric power supply consists of: quality of supplied electricity, dependability of supply, and quality of customer service. The quality of supplied electricity and dependability of the supply is essentially determined by the SEE dependability [1]. Dependability of the entire SEE consists of the operability degrees of individual system components responsible for electricity generation, transmission and distribution to customers. Unfortunately, in general, the importance and role of individual SEE elements is visible only at the time when they do not perform their functions properly, for example when there is no electricity supply caused by a failure. Unexpected depriving consumers of electricity supply may cause serious damage to property, and constitute a threat to people and equipment. Precise and unambiguous definition of dependability measures for each group of power equipment enables the identification of critical SEE items. This knowledge enables SEE performance improvement by way of upgrading the most failure-prone items, or use of newer technologies, thereby raising the dependability level of the entire SEE. Pursuant to current legal regulations, the domestic distribution system operators (DSOs) are responsible for the level of electricity supply dependability. The ongoing changes in the energy sector can be seen both in terms of changes in the ways of organizing its operations, as well as of a search for the best ways to improve the existing grid infrastructure’s performance. Not without significance is the current issue of the SEE implementation based on Smart Grid premises. The dependability indicators most frequently determined for power distribution systems include: number of shutdowns in a certain period of time, total duration of interruptions in the supply of electricity in a specified time period, number of faulty equipment items (in each group), and SAIFI, SAIDI and MAIFI indicators widely used in international practice. A very important problem encountered in the determination of grid dependability indicators is the lack of available data, due to the general absence of dependability services in utilities (ZE). Analyzing network failure, one should also be aware that this data is collected in a hierarchical manner, i.e. from individual energy districts (RE) to ZE headquarters, and then to the respective DSO branches. Typically only the averages of received dependability data are disclosed in reference publications. The lack of details of this data’s distribution between individual ZE utility companies does not allow for a complete analysis of the issue. This paper discusses the analysis of selected failure rates in two perspectives: dependability analysis as seen from the local utility company level, and for the entire domestic distribution power system. In the first part of the paper failure rates are analysed for five ZE utility companies operated by domestic DSOs. The second part presents an analysis of SAIDI, SAIFI and MAIFI indicators developed for the national distribution system on the basis of data posted on DSO websites in 2007–2012. Selected standards and legislation concerning the dependability One of the documents explaining notions related to dependability issues is PN-N-50191 93 standard “Glossary of electrical M. Kornatka | Acta Energetica 4/17 (2013) | 27–32