Distribution Reliability Analysis Program

IEEE/PES Transmission and Distribution Conference and Exposition: Latin America, São Paulo, Brazil, 2004

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The objective of this paper is to present a computer program developed for Windows to compute reliability indices for different customers and set of customers supplied by a same distribution feeder. This program deals with information obtained directly from utility database to create an equivalent network modeling and carry out contingency analytical simulations. The system’s average failure rates must be informed by the user, based on historical utility data, manufacturer test data or typical values.
The program enables to compute penaltiesand annual costa of energy interruptions and compare the obtained indices with the reIiability index targets set by the national regulatory agency (ANEEL) for the different sets of customers and distribution feeders under analysis.
The program allows to analyze the influencethe variation of the system rates and also modifications of the topology of the network and, thus, to carry out a sensitive study to verify the effect of some different protection equipment and modifications in the topology of the systems, justifying investmentsthat can improve the reliability,the power quality, and reduce costs of energy interruption end other related costs.


Despite the fact that around 80% of the power interruptions occur in the distribution systems, the reliability analysis of these systems had never received much attention until a few years ago. However, with the restructuring of the Brazilian electric sector and the privatization of the power distribution utilities, this situation has changed. In 1996, ANEEL - National Agency of Electric Power (regulatory agency) - was established to inspect the electric sector companies and, in 2000, it created the resolutions (laws) RES 024 and RES 522, introducing new indicators and reliability index targets for each set of customers and expressions for the calculation of penalties in the event of violations of these targets.
In order to meet the targets set by the regulatory agency, most distribution utilities began to digitally record their lines, equipment and history of interruptions, thus making it easier to develop computational programs and tools for analysis of power flow, short circuit and reliability of the distnbution systems.
Two different analyses are used to assess the reliability of the distribution systems: Historic and Predictive.
Through the historic analysis, one can obtain the indices referring to the intemptions occurred in the system for a given period of time, generating diagnoses of the system’s past behavior. While the predictive analysis calculates the future expectation of the system’s behavior in the medium and long terms, combining the components failure rates, the repair duration, switching time for restoring the reliability for different equipment and distribution line sections.
Considering that these factors are random, by nature, it is necessary to use average values computed from a database of interruptions and occurred failures. This way, it is possible to compute reliability indices for the whole electric system or set of customers, like the SAIFI (System Average Interruption Frequency Index and SAID1 (System Average Interruption Duration Index), as well as the reliability indices for each consumer. The method used in the predictive reliability analysis is the Analytical Method, faster and more accurate.


[1] ANEEL - Agência Nacional de Energia Elétrica, Resolução 24 / 2000, Brasil, 2000;
[2] Brown, R. E., "Electric Power Distribution Reliability", ABB Inc., Raleigh, North Carolina, 2002;
[3] Bilington, R. & Allan R. N.,"Reliability Evaluation of Power System", Pitman, N. Y,.1984;
[4] Lewis, E. E., "Introduction to Reliability Engineering", J. Wiley & Songs, Inc., N. Y., 1994.

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