Figure B.5—Probability of exactly f new MEDs in the next year of data
using M years of historical data
The consensus of the Design Working Group members was that five years was
the appropriate amount of
data to collect. The group felt that the distribution system would change enough to invalidate any extra
accuracy from more than five years of data.
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IEEE Std 1366-2012
IEEE Guide for Electric Power Distribution
Reliability Indices
Copyright © 2012 IEEE. All rights reserved.
31
Annex C
(informative)
Internal data subset
C.1 Calculation of reliability indices for subsets of data for internal company use
Reliability performance can be assessed for different purposes. It may be advantageous to calculate
reliability indices without planned interruptions in order to review performance during unplanned events. In
another case, it may be advantageous to review only sustained interruptions.
Assessment of performance
trends and goal setting should be based on normal event days (neglecting the impact of MEDs). Utilities
and regulators determine the most appropriate data to use for reliability performance monitoring. When
indices are calculated using partial data sets, the basis should be clearly defined for the users of the indices.
At
a minimum, reliability indices based on all collected data for a reporting period and analyzed as to
normal versus MED classifications should be provided. Indices based on subsets of
collected data may be
provided as specific needs dictate.
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