While effective vegetation management is fundamental to maintaining a reliable transmission system, it is not just as simple as that. Great River Energy (Elk River, Minnesota, U.S.) uses regular aerial patrols to proactively manage vegetation and other rights-of-way (ROW) issues. The North American Electric Reliability Corp. (NERC) recently applauded Great River Energy as an “Example of Excellence” for its vegetation management program, because it uses aerial patrols to ensure vegetation and other ROW issues are addressed before they can impact reliability, both from a system standpoint and from a customer viewpoint.
Great River Energy considers ROW vegetation maintenance a vitally important facet of its mission to provide members with reliable energy at competitive rates in harmony with a sustainable environment. We are a not-for-profit generation and transmission cooperative providing wholesale electric energy to 28 distribution cooperatives in Minnesota and Wisconsin. Approximately 1.7 million people get their power over the 4500 miles (7242 km) of transmission lines and through the 100 transmission substations that we own and maintain. Great River Energy is the second-largest power supplier in the state of Minnesota.
We have enhanced our vegetation management by implementing an aggressive aerial patrol program that greatly reduces the risk of vegetation contacts on bulk electric transmission facilities and also on the lower-voltage load-serving system that directly serves cooperative members. We try and balance the three R's: rates, reliability and responsiveness. Effectively managing our ROW is one way we meet our reliability objectives. Great River Energy is also highly aware of how vegetation contacts can have an adverse impact on the interconnected transmission system. We take this responsibility seriously, and we try and mitigate vegetation issues before they can cause an outage to a transmission facility.
Great River Energy conducts aerial patrols of transmission lines rated 115 kV and above every month; transmission lines that are rated 69 kV and below are patrolled on a bi-monthly basis. Burnett County Powerline Service, located near Luck, Wisconsin, performs these fixed-winged patrols. These aerial patrols are used not only to identify immediate vegetation concerns, but also can locate and identify transmission line hardware issues and various ROW infringements as well. There have been numerous instances of ROW infringement that have been identified through the use of these aerial patrols. Structure and structure hardware issues are also readily identified through these patrols. In the event that an issue is a public safety threat, the pilot also has direct radio contact with system operations staff, so that action can be taken immediately to effect repairs. The patrols have prevented outages from occurring and allowed us to manage our assets pro-actively and in a timely manner. The pilot is also equipped with a digital camera to give Great River Energy field operation staff a birds eye view of the equipment damage, ROW infringement, or vegetation issues on items the pilot deems to be serious in nature. Having a picture of the line from an aerial viewpoint is truly worth at least a thousand words. It gives field personnel an accurate picture of the severity of the problem.
Information received from the aerial patrols is entered into a central database on a weekly basis. The system forester directs items related to vegetation to the appropriate contract tree crew. We currently use Carr's Tree Service (Ottertail, Minnesota), Asplundh Tree Expert Co. (Willow Grove, Pennsylvania), Wright Tree Service (Des Moines, Iowa), Lake States Tree Service (Grand Rapids, Minnesota) and Central Applicators (Foley, Minnesota) to manage ROW needs.
We send structural issues to area line personnel. It is their responsibility to review the items and take appropriate action. “This process promotes ownership of the system in their area,” explains John Keen, supervisor of Transmission, Construction and Maintenance department work crews. “It provides information to the local crews and requires them to take action and assign a priority to the item noted in the patrol.”
Our Land Rights department addresses ROW infringement issues. Agents make the appropriate landowner contacts and make sure easement rights are adhered to. This is a very effective tool in maintaining our easement rights and making sure the ground clearances are what we expect, so we have proper line ratings specified for our transmission facilities.
CYCLICAL COLOR SURVEY
In addition to the routine aerial inspections, we conduct a cyclical ROW color-photo survey. Color photographs are taken of one-third of our corridors each fall. This survey provides a more complete picture of our ROW corridors, including overall vegetation growth rates. Personnel from Brainerd Helicopter Service (Brainerd, Minnesota) use a high-resolution digital camera to take the photos through an open door of the helicopter. We use the information from the color surveys and historical outage information to prioritize and schedule corridors for ROW maintenance in the coming year. This allows us to direct our vegetation management resources to the circuits that need attention the most.
We conduct the photo survey in the fall, because the changing tree foliage colors provides heightened contrast, allowing us to better detect species type, height and density. The color-photo survey helps locate danger trees within the ROW corridor that may pose a hazard during storm activity. The survey also helps to define access points by field crews for system restoration switching, when making any necessary emergency repairs and performing routine maintenance. The photographs help to pinpoint sensitive wetland locations that are important to public permitting entities and to identify and determine the size of buffer strips near waterways. The color photographs are placed on digital storage media to allow end users to manipulate photographs for their purposes. Each photograph is labeled with a line designation, structure number, date taken, disc number and picture number for future reference, and then it is cataloged and stored. This survey has been occurring since Great River Energy's inception in 1999. The results of these color-photo surveys have been extremely positive.
The color photographs have been an asset to our Transmission, Construction and Maintenance work group and the Land Rights department. The Land Rights department uses the photographs for estimating impacts on adjacent landowners for transmission line rebuild projects, routine maintenance projects, and also for landowner concerns or questions they may pose over the phone. “The color photographs allow us to see what the landowner is describing, and help us to address his or her issue in a timely and informed manner,” states Gary Ostrom, manager of Land Rights. Overall the color-photo survey has been a tremendous asset to Great River Energy. It saves time in vegetation and transmission line corridor surveying, provides early detection of potential ROW issues, and allows us to effectively allocate available physical and financial resources in our vegetation management program.
The aerial patrols and color surveying have played a large role in improving the transmission reliability to the member distribution substations that Great River Energy serves. Non-storm-related vegetation outages account for less than 1.5% of all outages recorded in a typical year. We also see added benefits of reducing equipment failure outages by fixing mechanical issues before a complete failure results in an extended outage. System operators have often received information via direct radio contact from the air patrol pilot about a damaged crossarm brace, loose hardware, floating conductors and damaged insulators. They immediately use this information to dispatch field personnel to secure the scene for public safety or to make any repairs that are necessary. We have also seen significant improvements in our transmission SAIDI and SAIFI indices. Although these indices are very dependent upon our Midwestern weather, part of the improvement can be attributed to making the appropriate repairs and dealing with vegetation issues before the result is a sustained outage to our customers.
Great River Energy understands the importance of good management of the ROW corridors. It is a key component to maintaining transmission reliability, a core philosophy that is strictly adhered to by Great River Energy staff. We continue to promote proactive management of ROW corridors on foreign lines that serve member distribution substations and continue to look for cost effective ways to provide reliability to our members.
Dick Pursley is the manager of system operations for Great River Energy. He has a BSEE degree and a MS degree in agricultural engineering from the University of Minnesota. Pursley is responsible for all real time operations at Great River Energy, including generation and load balancing, transmission system reliability, load management, and NERC standards compliance. He has been with Great River Energy since 1999 and in his current role since 2006. dpursley@GREnergy.com
Byron Johnson is the system forester for Great River Energy. Johnson holds a BS degree in forest resources from the University of Minnesota and is responsible for managing ROW vegetation maintenance, site maintenance, pole maintenance, and air patrol programs. Johnson has been with Great River Energy for 17 years and is also a member of the International Society of Arboriculture, Minnesota chapter of the ISA, the Utility Arborists Association, and the Society of American Foresters. bjohnson@GREnergy.com
EXPANSION OF PATROLS
PECO's outage management process begins with either a customer call, a last-gasp from a meter or a message from the Interactive Voice Response system. An Outage record is created and is sent to the OMS system. SCADA Events are sent directly to the OMS system. A dispatcher reviews the outage record and assigns it to an appropriate crew. When power is restored, the event is closed and validated with the power-up message from the meter.
Great River Energy recently expanded its aerial patrol program to include other regional utilities that have transmission facilities that serve our member cooperatives. We identified transmission lines that are important in serving the reliability needs of our member cooperative customers, and these low-voltage transmission lines are patrolled two times per year. In some cases, the costs of these patrols are partially subsidized by Great River Energy. Information from these patrols is sent to the respective utility. Great River Energy and the other utilities then work together to quickly resolve issues that result from the patrols. This cooperative effort has been eagerly accepted by these neighboring utilities and may be a precursor to more joint maintenance activities in an effort to improve reliability and safety throughout the region. This is another example of how we look for ways to improve the service we provide to our member cooperatives and their customers.