6.3. ERMUSR 01-13-2009~i
Elk River
Municipal Utilities
13069 Orono Parkway • P.O. Box 430
E(k River, MN 55330-0430
January 7, 2009
To: Elk River Municipal Utilities Commission
Jerry Takle
John Dietz
Jerry Gumphrey
From: Vance Zehringer
Subject: Electric Outage Report
Phone: 763.441.2020
Fax: 763.441.8099
The Minnesota Energy, Security and Reliability Act requires electric distribution utilities
to file an annual outage report to their governing bodies, which in our case, to the Elk
River Municipal Utilities commission.
ERMU continues to document 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. The attached spread sheet reflects the
outage history for 2008. Animals, fuse failures and branches caused the greatest number
of outages, but transformer failure accounted for the longest outages. Lightning also
accounted for a significant number or outages.
The table below reflects the number of customer outage minutes from 2002 to 2008
YEAR # OF CUSTOMERS # OF OUTAGE MINUTES # OF OUTAGES
2002 6669 356,340 50
2003 7193 39,285 54
2004 7773 393,926 84
2005 8398 558,140 59
2006 8804 314,510 73
2007 9162- 67,845 47
2008 9067 525,600 54
A number of reliability indexes are used in the electric industry to make it easier to
compare performance of electric utilities. These reliability indexes are:
2008 Electric Outage Report
Page 2 of 3
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 available in a time period. This is
normally expressed as a percentage.
ERMU's 2008 ASAI is 99.997%. 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. It is calculated by summing the customer minutes off during each
interruption in the time period and dividing this 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 2008 CAIDI is 28 minutes. Last years CAIDI was 63 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 that 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 2008 SAIDI is 17.3 minutes. Last years SAIDI was 7.4 minutes!
4. SAIFI (system average interruption frequency index)
This is defined as the average number of timers 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."
ERMU's 2008 SAIFI is .618. Last years SAIFI was .118!
2008 Electric Outage Report
Page 3 of 3
Another statistic staff gets concerned about is the average length of any outage.
ERMU's 2008 average length of outage is 99.3 minutes. Last year the average length
of outage was 68.8 minutes. Electric utilities with a high percentage of underground
facilities will exhibit higher length of outage time than electric utilities with more
overhead facilities.
Staff has reviewed these statistics in detail to find ways to improve. These statistics are
very good compared to other utilities. While other utility stats are difficult to obtain,
these are some typical numbers we have found:
MN Power Ottertail Xcel Connexus (2003 ERMU
SAIDI 143 min 115 to 70 min 153 to 99 min 45 min 17.3 min
SAIFI 1.2 2.1 to 1.25 1.36 to .96 .56 .618
CAIDI 120 min 59 to 55 min 112 to 99 min 80 min 28 min
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