Great Lakes Energy dedicated its efforts on system maintenance to four fundamental tasks and slashed SAIDI by more than 70% in four years.
Great Lakes Energy, like many cooperatives across the nation, spent half a decade in the late 1990s focusing its member-satisfaction efforts on diversification of products and services. These included buying and running a propane company, and establishing an electrical services company, a home insulating business and several communications-related services offered to members and non-members alike.
While these activities were being developed and implemented, the core business of this distribution cooperative — the delivery of energy to the end user — suffered from a lack of attention and resources. Consequently, member satisfaction and system reliability declined.
In late 2004, Great Lakes Energy (GLE) embarked on a systemwide refocusing of resources to return the utility back to basics and improve member satisfaction and overall system reliability. Improving reliability was no small task for a system that included 14,000 miles (22,531 km) of distribution line spanning over a 26-county service territory providing electric service to 125,000 metering locations across the state of Michigan. Senior staff established several teams of key stakeholders to evaluate the in-place processes and programs and develop recommendations on how to improve them.
The teams of stakeholders recommended several key action items:
Re-establish an integrated vegetation management program
Complete a full-system sectionalizing study
Integrated Vegetation Management
Create an overhead and underground line inspection program
Develop a worst-performing circuit maintenance process.
GLE's ultimate goal is to be in the top quartile of cooperatives nationally in reliability. Using IEEE Standard 1366 outage tracking methodology, GLE is tracking and charting the goal on a daily system average interruption duration index (SAIDI) basis. To date, the key action items have contributed significantly to a reduction of the total system SAIDI from a staggering 594 minutes in 2005 to 169 minutes in 2009.
Historically, GLE's vegetation management program ran under the philosophy that the budget drove the vegetation work to be completed that year. In 2005, GLE shifted its philosophy to letting the work drive the required budget. GLE performed a field audit and determined that a mechanical re-clear cycle of seven years would be needed to properly manage the utility's distribution line vegetation.
Systemwide Sectionalizing Study
GLE is also on a seven-year herbicide spraying cycle, although because of growth rates and the geography of the distribution system, the south half of the system is sprayed one year after the mechanical re-clear, and the north half of the system is sprayed two years after the mechanical re-clear. Because GLE's members are also owners, member satisfaction is a high priority. When it comes to herbicide application, GLE requires a positive contact, a “yes,” from members on all property, vacant or otherwise, before herbicide is applied.
Every year, a span-by-span audit is completed for the following year's cycle of vegetation work. During the audit, a vegetation management field representative records the type and amount of trimming and ground work required at each span. Once a contractor completes the required tree trimming, ground work or herbicide application, a post-inspection is performed and a punch list is created and completed, ensuring the work was done to standards.
The vegetation management group inspects approximately one-third of GLE's 236 mainline feeders from the substation recloser to the first main line protective device annually to ensure danger trees and cycle busters are treated accordingly and to prevent a complete feeder outage, thus reducing the large contributors to the total systemwide SAIDI and system average interruption frequency index (SAIFI). Distribution circuits serving key accounts are inspected annually from the substation recloser to the key account member's primary metering location, minimizing vegetation-related power-quality problems for the cooperative's largest electrical users.
GLE redefined how its distribution system would respond when experiencing a fault. Many substation reclosers on the system were older three-phase devices that had a limited ability to coordinate with downstream reclosers and fuses. Most of the substation reclosers were upgraded to electronic controls with single-phase trip, single-phase lockout capabilities, reducing feeder blinks and feeder outages from three phases to potentially one phase depending on the type of fault. The upgraded substation recloser controls allowed greater flexibility down line, as the sectionalizing group recommended the installation of a midpoint protective device either on the center of the main line or on the main line such that the total numbers of members on the circuit were split 50-50 on each side of the device.
GLE completed a full coordination/sectionalizing study to optimize the system under a fault condition and minimize the impact to members. The utility also developed a fuse-saving versus fuse-sacrificing scheme to manage temporary faults.
Worst-Performing Circuits and Maintenance
GLE averages about nine electric members per mile (6.6 members per kilometer) of distribution line. The sectionalizing team determined that if a tap off the main line has nine or fewer members, the tap would be coordinated under a fuse-sacrificing scheme. The fuse would melt immediately without allowing the upstream recloser to operate. If the tap off the main line has 10 or more members, the tap would be coordinated under a fuse-saving scheme, and the upstream recloser would be given a chance to operate up to two times to clear a temporary fault before allowing the fuse to melt.
As a result of the sectionalizing study and to further reduce the impacts of outages, thousands of fused cutouts were recommended and installed on the distribution system, resulting in a significant reduction in the system SAIFI.
GLE spent approximately US$3.5 million to upgrade and update the distribution system equipment and protection scheme, thus preparing it for future supervisory control and data acquisition (SCADA) and distribution automation (DA) schemes. Using electronic midpoint feeder reclosers and a motor-operated air-break tie switch between the feeders allows DA schemes to be deployed where practical. The DA schemes enable the distribution system to reconfigure itself automatically upon loss of voltage, providing a circuit to be partially fed from an adjacent substation in the event of a feeder or substation outage.
A worst-performing circuit is one on which members experience more than twice the average system SAIDI minutes. GLE's strategy is to identify a set of worst-performing circuits each year and perform strategic equipment or environmental upgrades during the year to improve their reliability. In many cases after the strategic upgrades, today's worst-performing circuits become the future's best-performing circuits.
Historically, maintenance work was done when the crews had spare time between new services, work plan construction projects, responding to outages and all their other routine work. Currently, GLE has two dedicated three-man maintenance crews and five different contract companies performing system maintenance work. The work includes the installation of wildlife protectors on transformer bushings to prevent outages from wildlife encounters, finding and replacing failed or failing equipment such as blown arresters and old cutouts, and finding and replacing equipment with a known high-failure rate such as aluminum deadend bells. Usually the equipment being replaced is more than 30 years old and has reached the end of its useful life.
Change is Good
GLE generates maintenance work orders for the worst-performing circuits through the line inspection program. Line inspectors systematically inspect the worst-performing circuits each year, noting on each pole the required maintenance work that needs to be completed. A priority level for the required work is established based on the severity of the problems encountered. The maintenance supervisor coordinates all of the work, and emergent repairs such as cracked insulators, burning cutouts, broken strands and braces are completed the same day or next day.
The utility also completes line inspections on underground facilities on a three-year cycle. Inspectors review the accessibility of the enclosure and the external condition. Based on the inspection, the enclosure may be refinished or replaced. Internally, the enclosure is inspected for snakes, bees and other critters that create a home inside enclosures. Inspectors also verify the enclosure is properly grounded, ensure elbows have not backed off the bushings and make notes to replace failed elbow arresters. GLE spends approximately $3.5 million annually on line maintenance activities for the worst-performing circuit process and line inspections. Approximately 70,000 members are benefiting from the improved SAIDI and SAIFI numbers on circuits directly related to maintenance work performed on the circuits.
Pole inspections and testing are completed on a 10-year cycle, with approximately 25,000 poles inspected annually. The inspection contractors use sounding, boring and sonic testing depending on the circumstances. Approximately 300 poles are replaced annually and some of the poles being replaced are the original poles installed by the cooperative in the late 1930s.
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GLE recognized a change in direction with system maintenance was necessary to be in the top national reliability quartile of cooperatives and to improve its member satisfaction. System maintenance is no longer a program operated in a run-to-failure mode or a program that is worked on when it fits into the everyday work schedule. System maintenance is a dedicated process requiring a complete team effort by many different departments. Using the IEEE Standard 1366 methodology since its inception, GLE has not only made a significant reduction in both SAIDI and SAIFI, but it has also increased its member satisfaction.
Scott Blecke (firstname.lastname@example.org) is the key accounts manager/engineer at Great Lakes Energy (GLE). He works with the engineering group and provides technical assistance to GLE's commercial and industrial members. He is a member of IEEE and a registered professional engineer in the state of Michigan. Blecke received his BSEE degree from Michigan Technological University.
Great Lakes Energy www.gtlakes.com