Let me put it simply: Trees and transmission lines don’t mix!” says Mark Davis, executive vice president and COO of transmission-only utility American Transmission Co. (ATC). Add in a third element — storms — and Davis’s discord between trees and lines turns into a cacophony of trouble, with storms tossing trees branches about and upending seemingly stolid tree trunks as if they were young saplings. Utility lines and towers are both directly and indirectly in a storm’s path, too. It might be lighting or wind itself that takes down a line, or it might be some object — including vegetation — that causes a storm outage.
What are utilities to do? The force of Mother Nature hardly can be denied in a major storm. Fortunately, there are vegetation management strategies and techniques that can be deployed to minimize — at least to some degree — the danger that storms present to electric power reliability.
A Well-Managed Program
At the Sacramento Municipal Utility District (SMUD), for instance, Steve Hallmark’s group has been tracking tree-related outages for most of the past 20 years. The tracking was instigated by California Public Utilities Commission (PUC) rules adopted in 1997 that required utilities to provide minimum clearance for primary distribution voltages. The first thing SMUD did was hire a professional vegetation manager — Hallmark himself — to implement a comprehensive vegetation management program. One of the first things Hallmark did was institute a vegetation management program focused on categorizing, pruning and removing trees that fall into one of three cycles: routine, cycle buster or out of cycle.
The routine cycle is designed to maintain the majority of trees to meet the radial clearance specified by the California PUC for a three-year period. Cycle busters are trees that will not make it three years and, therefore, are pruned 18 months after the routine cycle is completed. Finally, out-of-cycle trees are those that do not have adequate clearance and include all storm- or emergency-related tree work.
SMUD found categorizing and pruning trees in this manner has led to a rapid and sustained drop in outages caused by trees compromising lines. In fact, tree-related outages, which were in the 300-per-year to 700-per-year range in the late 1990s, dropped after the first routine cycle was completed in 2001 and have stayed down in the 100-per-year to 200-per-year range ever since, even dropping below 100 in 2007.
“The outage data includes major storm events, which demonstrates that a well-managed and properly funded vegetation management program will enable a utility to perform exceptionally well as it relates to tree-related outages,” Hallmark noted. “An ancillary benefit is that customers are less inconvenienced by power outages, especially during storm events.”
A Core Element
“Vegetation management, in general, is a core element of any good utility safety and reliability practice,” said Davis. Referencing his earlier admonition that “trees and transmission lines do not mix,” Davis says that, on the prevention side, utilities need a strong integrated vegetation management (IVM) program to ensure rights-of-way are clear and low-growth species can evolve.
“The second aspect of a good IVM is you have to have access to your rights-of-way,” Davis added. “In the event you have a line down or a pole down, you need access to the structures in order to have timely service restoration.”
According to Davis, a challenging aspect of performing robust IVM comes in working with landowners who may not want a tree, or trees, to come down. “Our goal is to minimize the impact on landowner properties while achieving our safety and reliability objectives. Admittedly, that is not an easy task.”
As a transmission-only utility, ATC’s stakes for reliability and storm recovery could typically be wider-spread than distribution utilities,” Davis noted. “Above 200 kV, we are within FERC regulations, and the approach is a zero-tolerance mindset. We don’t take many risks at this level. We have to make tough decisions, and the consequence of being wrong could be significant.”
Davis called the IVM concept “the new normal” for utilities and offered an additional, rather interesting observation: “A lot of this started with the 2003 blackout, some of which was due to poor vegetation management. Over the years, utilities have realized that good vegetation management practices benefit us all. This is one of the true noncompetitive aspects of the utility business. I’m impressed with how much open sharing there is in the industry in terms of best practices in IVM. At ATC, reliability is of the utmost importance and a good IVM is very much a part of that.”
The Compounding Effects
With or without a solid IVM, storms will continue to bring down lines and result in at least some power outages, either on the transmission or distribution side. When that happens, enter the contractors — tree-trimming specialists who partner with utilities to get power back on as quickly and safely as possible.
Wright Tree Service is one of the largest vegetation management contractors in the U.S., with more than 2,600 employees across 11 geographic divisions throughout the country. Fittingly enough, Wright’s website has two buttons at the top of its home page: vegetation management and storm restoration.
According to Wright Tree Service President and COO Will Nutter, Wright and other contractors start negotiating storm agreements for storm-prone areas from early September through early spring to be ready for tornado, thunderstorm and even hurricane seasons. “We need to be prepared to go to work when the storm hits, and that means a ton of work is done on an annual basis,” Nutter explained. “We need tiers of pricing for the various types of labor that are going to be involved, mileage rates and per diems. When guys get on the road, they need to know what the rates are.”
On site, the first meeting is an orientation focusing largely on safety, Nutter noted. Storm crews, he explained, are often new crews with members new to each other, and often the crews are working in locations other than their local service territory. “We need to find out what the safety requirements and practices are,” he said. “Will we need body harnesses or body belts? What are the communications protocols? We cover lockout tag-out so there are no surprises. The No. 1 focus is that nobody gets hurt.”
If the event or outage is large enough, the company will stage as many workers as it can as close to the recovery area as is feasible, Nutter shared. Next, he added, triage is performed, with usually one or more contractors assigned to construction companies and utility crews so they can work in partnership to clear access to lines. Work in a storm zone for a contractor is often challenging and frequently done in very trying weather conditions, Nutter said.
Something else that can be easily overlooked if a utility or contractor is not paying close attention, Nutter warned, is the aftereffects of storms on both vegetation and power systems. “Let’s say you have an ice storm, for example, and the trees are completely iced up and bent over,” Nutter said. “If you just did triage, maybe you missed trees and branches that will impact the lines later, as the ice melts. You don’t always realize the compounding effects of bad weather.”
Since weather can be both unpredictable and unavoidable, forward-looking utilities and tree companies go into every changing season with a plan, mapping out potential future trouble spots and marshaling resources for when the wind howls, lightning strikes, or fires or floods come. And while “triage” is the word of the day when lines go down, once a storm has passed, utility vegetation management staff are well advised to review their recent lessons learned in order to be even better prepared for the next time.
Using Automatic Vehicle Locating for Efficient Storm Response
By Kristin Wild, Asplundh Tree Expert Co.
Many utilities have installed GPS-based automatic vehicle locating (AVL) in service trucks for tracking purposes and to improve dispatching during emergencies. The Asplundh Tree Expert Co. has its own AVL system, called AVMS (automatic vehicle management system).
Approximately 20,000 Asplundh trucks are equipped with a GPS receiver and a modem to collect and transmit data on truck location, engine start and stop times, and auxiliary motor usage every 15 seconds. This and other operational data is sent to a central server every two minutes and uploaded into a visual display that system users (with proper login credentials) can access via tablet or smart phone. This allows foresters and dispatchers to “see” mobilized and local crews.
Asplundh provides its customer utilities with a distilled version of its AVL system called AVMS Live. AVMS Live can even be configured as a layer within the utility’s GIS database so that tree crews can be seen in relation to the system’s circuits and other geographical features.
AVMS Live users simply click on a vehicle icon to get its truck number and foreperson, and to tell the utility’s “bird dog” (or vegetation management contractor’s representative) to direct crews to the nearest or next trouble spot. With Asplundh crews, this process is soon to be supplanted by text messaging sent to vehicles equipped with Truck-as-a-Hub Wi-Fi hotspot capability. A tablet computer assigned to each vehicle provides turn-by-turn directions to the trouble spot. The crew is also able to text back any unforeseen problems as well as confirm that the assigned work was completed, when done.
More than 150 utilities use AVMS Live today. The system allows the nearest tree crew to respond to a trouble call instead of the next available crew, which might be much farther away. Additional benefits include increased driver safety and security. It all adds up to a safer, more efficient storm-restoration process, getting the trees off of the lines and the power back on for every customer as quickly as possible.