Download PDFAbstract:
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.
Introduction:
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.
References:
[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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