Nashville Electric Service

General Company Information

Municipality-owned Nashville Electric Service (NES) has operated in Central Tennessee for more than 68 years. NES serves more than 348,000 customers in 5,000 line miles in Nashville’s Davidson County. It also serves portions of six other counties: Wilson, Williamson, Cheathan, Robertson, Sumner, and Rutherford.

The Problem

NES’s tree-related outages per 100 miles of line and per 1,000 trees were 10 times more than that of best-practice utilities. In some areas of the system, it had been 7-10 years since trees were trimmed for conductors. Some NES customers were experiencing 7,000-8,000 interruptions per years. Outage data was provided by NES from July 2000 thru February 2001. In these 8 months, NES experienced 5,827 outages. 2,654 of these outages were tree-related. NES had an average of 56 tree-related outages per 100 miles. Tree crew production was well below expectations. NES needed redirection of maintenance dollars, and needed to accelerate their vegetation management program.

How did they find or hear about ACRT?

ACRT had a significant presence in the Tennessee area, and NES talked to all of our customers and went in the field to look at operations visiting Southwest Tennessee Electric (SWTEMC) and meeting with ACRT’s operations manager and lead forester at SWTEMC. After that meeting, NES had a good understanding of the ACRT business model. NES needed to start a vegetation management program and opened the service up for bid in 2002. ACRT put in for the bid and was awarded the contract. We started operations July 1, 2002.

Why did they choose ACRT?

NES chose ACRT because of its history, proposal and professionalism in assuring NES they could help them to achieve their vegetation management goals.

The Solution

What did ACRT recommend to help NES?

ACRT suggested that NES take steps to improve the effectiveness of line clearance work as measured by tree-related outages.

We recommended that these steps include:

• Adequate, needs-based line clearance, funding targeted toward reliability improvement.
• NES should no longer do round-over or stub pruning. All pruning should be lateral pruning done to ISA standards.
• NES should aggressively remove trees and brush during their first trim cycle that can be removed for about the same cost of trimming.
• NES should use herbicide on freshly cut stumps to prevent re-sprouting. Place an increase focus on tree contractor performance.
• NES should convey to the public that it has a responsibility to maintain vegetation that has an impact on the safety and reliability of the electrical system.
• NES should utilize work planners to collect data, mark trees and notify property owners of work that will be done on their property. Work data will be collected on handheld computer using ArcPad (GIS software). The data will be stored on the NES network for use by the vegetation management department.
• NES should continue to use the tree replacement and stump grinding method in regards to achieving more removals. ACRT auditors will audit work done by contractors to ensure that work is done properly and complete. Trimming should be done on a 3-year trim cycle. Trimming clearances will be based on the type of tree being trimmed. Faster growing trees should get more clearance, and slower growing trees should get less clearance.

What were the results?

The results have been very positive. ACRT has completed its first three-year trim cycle and is currently working on the second cycle now. We have successfully removed more than 2 million trees on the NES system, driving the future costs of maintenance down. NES has had a 20 percent increase in its system reliability. Restoration time has been cut in half. NES has had a major drop in their overtime needed from their line department saving them money year after year. Areas of the system that were not safe to work during severe storms are now accessible and safer for their line department. Equipment is now visible and NES is upgrading a great deal of its older hardware.

In their own words.

“Nashville Electric Service appreciates the efforts of ACRT work planners and auditors in assisting us in establishing a three-year trim cycle on our systems.” -- Glenn Springer, Vegetation Management, Section Manager