Spacer Cable Gets Kentucky Electric Co-op out of Tight Spots

For Kentucky’s Nolin Rural Electric Cooperative Corp. (RECC), projected growth associated with Fort Knox expansion has meant the need to construct one new electricity substation, with another one in the works and future plans to add more substations to meet the electricity needs of the growing population.

Hendrix Figure 2

For Kentucky’s Nolin Rural Electric Cooperative Corp. (RECC), projected growth associated with Fort Knox expansion has meant the need to construct one new electricity substation, with another one in the works and future plans to add more substations to meet the electricity needs of the growing population.

Since there can be significant issues with electrical clearance and reliability using bare wire at substations, Nolin RECC uses spacer cable systems, which offer reduced spacing between conductors and reduced clearance requirements. The ability to put multiple circuits on a pole reduces right-of-way requirements at substation exits and along the distribution line where multiple circuits are required. This allows more efficient use of limited space in substations. In addition, the cable covering and high mechanical strength of spacer cable systems provides increased reliability on the critical feeder circuits at substation exits—something that came in useful after a severe ice storm in 2009.

Nolin RECC currently uses spacer cable systems supplied by Hendrix Aerial Cable Systems for 67 feeders at 22 substations. In addition, Hendrix spacer cable systems are used in other areas where space is tight, including road construction in close proximity to houses and trees. Future plans include investigating other situations where spacer cable systems might provide benefits and incorporating appropriate projects into its work plan.

Hendrix Figure 2
Nolin spacer cable system, showing messenger cable that supports the structure, polyethylene spacers to hold the cable across spans and covered conductor cable.

Population Growth Fuels Need for New Substations

Nolin RECC serves nine counties in central Kentucky, about 40 miles south of Louisville. The system has about 3,000 miles of line, with roughly 32,500 meters in service. Generation and transmission (G&T) is primarily from East Kentucky Power, a coal-fired plant, with a small percentage generated by a landfill gas facility in Hardin County.

One of Nolin RECC’s key growth engines has been the expansion of Fort Knox, which came out a winner in the Department of Defense’s Base Realignment and Closure (BRAC) process. According to Nolin RECC’s engineering superintendent, Greg Harrington, the Army moved its entire human resource function to Fort Knox, opening a 900,000 square foot facility behind the Pentagon. Some 36,000 employees will work at the facility. In addition, a brigade from Germany will relocate to the base next year.

“Our service territory is growing fast,” Harrington said. “Employees and their families are flocking to the area and we are doing some serious planning around adding necessary infrastructure to serve the need.”

Key to that infrastructure growth has been the need to add electricity substations. A substation was added some five years ago, one came on line in 2009, and another is planned for the next few years—with a projection that another substation will be added about every three to four years.

According to Harrington, Nolin RECC uses spacer cable systems to deal with the issue of space constraints around substations. Since 1986 Nolin RECC has used spacer cable systems supplied by Hendrix, a New Hampshire-based Marmon Berkshire Hathaway firm that provides underground cable, spacer cable, tree wire, insulators and other overhead accessory products. The original circuit installed in 1986 has only experienced one outage since installation, and that was due to an improper connection.

Spacer cable systems have been used by utilities for many years to improve the reliability and power quality of primary distribution systems while making them more resistant to storm damage. The compact configuration and reduced clearance requirements allow multiple circuits to be installed on a single pole—combating right-of-way problems and saving money by reducing the number of poles required. Over- or under-building spacer cable systems in substation exits can greatly reduce the cost of adding capacity.

A spacer cable system consists of a messenger cable that supports the structure, polyethylene spacers to hold the cable across spans and covered conductor cable.

The messenger cable is the support member for the structure. Messenger wires are available in several varieties, depending on the application, and serve as both system neutral and lightning shield. Mechanical strength makes the messenger wires suitable for long spans.

Clipped to the top of the messenger wire is a series of spacers. After being installed and attached to the messenger, the spacers support, separate and clamp the phase conductors in a triangular, diamond-shaped configuration.

“They look like a series of hanging stars,” Harrington said, who noted that the spacers are placed between spans of about 30 to 40 feet.

The spacers are molded using a proprietary, gray, track resistant, high-density polyethylene. They feature quick, easy installation and removal. No ring ties are required; there are patented integral clamps for conductors and messenger. The clamp design accommodates a full range of conductor and messenger sizes. The wedge-shaped messenger hook provides maximum grip.

The spacers have very good weather washing characteristics. Long leakage distance resists flashovers, close phase spacing minimizes voltage drop and the design provides high short circuit strength. The spacers are highly resistant to shock, impact or rifle fire, and can be installed with hot line tools.

The individual cables used in the spacer cable system contain a three-layer covering, which can withstand temporary contact with tree branches and other vegetation—reducing outages and improving power quality. This, along with the compact configuration of the system, greatly reduces the need for vegetation removal during circuit installation—significantly cutting tree trimming costs. The covering also protects wildlife from exposure to lethal currents.

Covered conductors consist of stranded hard drawn aluminum conductors with three extruded layers; the thickness depends on the voltage rating. Hendrix’s proprietary, high-density outer layer resists abrasion, electrical tracking and ultraviolet (UV) degradation. In addition, reduced National Electrical Safety Code (NESC) phase spacing is possible because of high impulse strength covering.

“Open wire systems have steel running through the cable, and the outside is aluminum. The spacer cable system is all aluminum, so it has a better current carrying capacity,” Harrington said.

Hendrix Figure 1
Placing multiple circuits on a pole reduces right-of-way requirements at substation exits and makes more efficient use of limited space.

Nolin System Substations Take Advantage of Spacer Cable Systems

In the Nolin system, about 39 of the 3,000 miles of line use spacer cable systems. There are currently 67 feeders that come out of 22 substations, and most of these use the spacer cable system. In addition, the spacer cable system is used in other instances where there are two circuits on the same pole to avoid clearance issues. Instead of requiring larger poles, Nolin can use spacer cable on brackets affixed to each side of the pole, straight down the pole route.

“The jacket surrounding the conductor on spacer cable allows the technician to come out of some very tight spots. Using open wire is more difficult because the technician must have a greater amount of clearance.

“Typically four to five circuits have to come out of the substation, and, if open wire is used, it becomes congested. Using spacer cable let us get outside the substation easily—we’ve run as many as 10 to 15 spans outside a substation using the spacer cable solution,” Harrington said.

As an added bonus, areas that used spacer cables were considerably less affected in a serious ice storm in February 2009, during which 92 percent of customers were without power.

“We did not lose a single pole or span of wire in the areas where spacer cables were used,” Harrington said. “The areas were affected, but they lost power on the circuit where it went to open wire.”

Using spacer cable systems has been so successful that Nolin RECC has started to look at other situations where its use would be appropriate.

“As we review our work plan every two to three years, we look for other areas where spacer cable would be beneficial,” Harrington said. “Sometimes the right-of-way we have through areas with trees is too narrow to cut as aggressively as we need, for example, and we would probably use spacer cable in that situation. We recently used spacer cable on a road widening project in which the road was close to houses, and our utility easement did not give us a full amount of clearance.”

Spacer cable systems are Harrington’s product of choice for getting in and out of tight spots where traditional open wire conductor would be difficult to use.

“We have found that spacer cable systems work extremely well in substations, as well as a variety of other spots where space is an issue,” Harrington said.

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