5.3. ERMUSR 01-09-2007 Elk River
Municipal Utilities
13069 Orono Parkway phone: 763.441.2020
Elk River,MN 55330 Fax:763.441.8099
January 3, 2007
To: Elk River Municipal Utilities Commission
Jerry Trkle
John Dietz
Jim Tralle
From: Bryan Adams
Subject: Electric Outage Report
The Minnesota Energy, Security and Reliability Act enacted in 2001, contains a distribution
reliability section. One section of this legislation requires, on an annual basis, an outage
report be submitted to their governing bodies, which in our case, is the Elk River Municipal
Utilities Commission.
Your staff, for a number of years, has been documenting electrical outages to keep track of
causes, number of customers out of power and for how long in an effort to track trends and
resolve continued outage problems. This tracking now has the benefit of complying with the
distribution reliability section of this legislation. Our electric outage reporting has been
formalized so we can better track and analyze the number and causes of our outages. The
attached two page spread sheet reflects the outage history for 2006. Animals (squirrels) and
3rd party dig-ins are the cause of the greatest number of outages. Construction issues (pole
arm failure, slapping phase together while stringing, and wiring issue at Otsego Substation)
caused the greatest number of customer minute outages at 75.1%. There is no alarming
trends or patterns.
The table below reflects the number of customer minutes outages from 2002 to 2006.
YEAR # OF CUSTOMERS #CUSTOMER—MUNUTES OF OUTAGES
2002 6669 356,340
2003 7193 39,285
2004 7773 393,326
2005 8398 558,140
2006 8804 314,510
A number of reliability indexes are used in the electric industry to make it easier to compare
performance of electrical utilities. These reliability indexes are:
1. ASAI (average service availability index)
ASAI is a measure of the average availability of the sub-transmission and distribution
systems to serve customers. It is the ratio of the total customer minutes that service was
available to the total customer minutes demanded in a time period. It is normally expressed
as a percentage.
ERMU's 2006 ASAI is 99.99%. This is a very good percentage for any utility.
2. CAIDI (customer average interruption duration index)
This is defined as the average length of an interruption, weighted by the number of customers
affected, for customers interrupted during a specific time period. It is calculated by summing
the customer minutes off during each interruption in the time period and dividing this sum by
the number of customers experiencing one or more sustained interruptions during the time
period. The resulting unit is minutes. The index enables utilities to report the average
duration of a customer outage for those customers affected.
ERMU's 2006 CAIDI is 105 minutes.
3. SAIDI (system average interruption duration index)
This is defined as the average interruption duration for customers served during a specified
time period. It is determined by summing the customer-minutes off for each interruption
during a specified time period and dividing the sum by the average number of customers
served during that period. The unit is minutes. This index enables the utility to report how
many minutes customers would have been out of service if all customers were out at one
time.
ERMU's 2006 SAIDI is 35.72 minutes.
4. SAIFI (system average interruption frequency index)
This is defined as the average number of times that a customer is interrupted during a
specified time period. It is determined by dividing the total number of customers interrupted
in a time period by the average number of customers served. The resulting unit is
"interruptions per customer". Separate SAIFI indexes are sometimes calculated for long and
for short interruptions.
ERMU's 2006 SAIFI is .342.
Another statistic staff gets concerned about is the overage length of any outage. ERMU's
2006 average length of outage is 95.07 minutes. Electric utilities with a high percent of
underground facilities will exhibit higher length of outage times than electric utilities with
high percent of overhead facilities.
Staff has reviewed these statistics in detail to find ways to improve. These statistics are in
general very complementary to ERMU. Glenn Sundeen and his department continue to do
an outstanding job in constructing, operating and maintaining an electrical system
particularly in a fast growing area.
Other utilities statistics on CAIDI, SAIDI, and SAIFI are still difficult to obtain and entities
play some games with these numbers. Below is a table reflecting local utilities statistics.
SAIDI SAIFI CAIDI
Minnesota Power 142 1.04 91
Otter Tail Power 64 to 46 19 to 9 5 to 3.0 ?
Xcel 170 to 120 1.3 to 1.1 132 to 100
Elk River Municipal Utilities 36 .342 105
Connexus 2003 Data 45 .56 80
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