Of course, in a new era of survivalism and in a storm-prone locale where more and more Cleveland and Bradley County homeowners are buying their own generators to offset the short-term effects of such outages, the wait times for return-of-service don’t seem as long.
But a Reliability Indices Comparison report for 2012 shows a lot more Cleveland Utilities customers enjoyed the comforts of consistent electrical service than those who had to live without.
In a recent monthly update by CU Electric Division Vice President Bart Borden, members of the Cleveland Board of Public Utilities received a lesson in statistical data, most of which came with complex acronyms requiring some detailed explanations by the Electric Division leader.
Once the informational dust had settled, it became apparent Cleveland Utilities customers fared OK in electric service reliability, both in consistency of power and infrequency of service interruptions.
For instance, throughout the entire year of 2012, a utility industry measure called the Average Service Availability Index (ASAI) showed 99.9886 percent of CU customers had electric power service in total customer minutes. ASAI takes into account conventional service, normal conditions and traditional interruptions.
The Reliability Indices Comparison Report “... excludes major storms such as the tornado events of April 2011 and March 2012,” Borden explained. Including data from these infrequent natural disasters would skew ASAI reliability data.
Borden also pointed out power outages are defined as “... greater than 1.05 minutes in duration.”
A few other measures used within the utility industry to gauge its effectiveness, and which Borden included in his reliability report, include:
1. Customer Average Interruption Duration Index (CAIDI), which gives the average outage duration that any given customer experiences, shows the CU rate in 2012 to be 56.45 minutes. Borden described the CAIDI rate to mean “average minutes interrupted per interrupted customer.” The average length for North American utilities, according to IEEE (the Institute of Electrical and Electronics Engineers), is 1.36 hours.
2. System Average Interruption Duration Index (SAIDI), which gives the average outage duration for each customer served, shows the CU rate in 2012 to be 60.25 minutes. Borden described the SAIDI rate to mean “average minutes interrupted per customer for all customers.” The average North American utility rate is 1.50 hours, according to IEEE.
3. System Average Interruption Frequency Index (SAIFI), which gives the average number of interruptions that a customer would experience, shows the CU rate in 2012 to be 1.07. Borden described the SAIFI to mean the “number of long interruptions per customer for all customers.” IEEE reports the average North American utility rate to be 1.10 interruptions per customer.
Data from the American Public Power Association shows the CU reliability indices compare favorably to other power companies within APPA Region 7. In 2012, CU’s ASAI of 99.9886 was lower than the region’s 99.978; the CU CAIDI of 56.45 was lower than the region’s 56.64; and the CU SAIFI of 1.07 was considerably lower than the region’s 1.31. Only CU’s SAIDI number of 60.25 minutes was higher than the region rate of 60.16.
Borden’s detailed report pointed to the benefits of installing “distribution automation” equipment which is now under way by Cleveland Utilities. Board members previously approved the purchase of certain automated equipment items; however, in order to keep the Electric Division within budget, other automation pieces will be added in a later budget.
This system of utility automation is referred to as Supervisory Control And Data Acquisition (SCADA).
“[An] APPA report indicates utilities with a SCADA system reported 35 percent less interruptions and 31 percent less minutes for interruptions,” Borden told board members in his report.
He also pointed to similar data provided by a neighboring utility which is using distribution automation.
“The Electric Power Board of Chattanooga reported a reduction in their SAIDI from 109 minutes to 82.5 minutes since 2011 due to distribution automation equipment,” Borden said. “This is a 24 percent improvement.”
He pointed out, “Cleveland Utilities is [already] 22.25 minutes less average outage duration for all customers, but does not have as much rural service territory [as Chattanooga’s EPB].”
Borden’s technical report also included some less complicated terms, some more familiar faces and a few eye-opening results for 2012.
For instance, over the course of last year, the causes of electric service interruptions to CU customers, by percent, included: Overhead equipment failure, 14 percent; underground equipment failure, 3 percent; weather-related, 6 percent; trees, 18 percent; human-created, 7 percent; unknown, 20 percent; and other, 3 percent.
But CU’s leading cause of service interruptions in 2012? The crown goes to wildlife, 32 percent.
And the most common culprit among critters? Squirrels.