Unique spacer cable system powers renewable energy plant pipeline

When the L'Anse Warden Electric Company in Michigan's Upper Peninsula wanted to reduce road traffic associated with biomass trucked to its electric power generation station, it needed power for an above ground pipeline that would pump the material from an access point along a major highway to the plant. The distribution wiring solution required clearances considered safe enough to permit employees to conduct maintenance activities on the pipeline. L'Anse Warden found that a standard spacer cable system, coupled with underground residential distribution (URD) cable, gave the company the clearance they needed for worker safety while also providing the ability to use existing poles, thus saving significantly on overall costs. The system was supplied by Hendrix Aerial Cable & Systems, headquartered in Milford, NH.

L'Anse Warden Electric Company, LLC, (LWEC) is a 20 megawatt biomass-fueled electric plant, located near Lake Superior in the Upper Peninsula region of Michigan. LWEC is a subsidiary of Traxys North America, LLC, which operates several electric power generation stations in the area and is a licensed alternative electric supplier (AES) to the state.

LWEC was converted from a coal, oil and natural gas-fired station in 2009, and burns forest products (woodchips, bark and fines), paper mill wood residues, railroad ties, and tire chips. This renewable energy feedstock was trucked from Highway 41 to downtown L'Anse, costing time and money as trucks wound their way through narrow local roads to the power plant. LWEC decided to install a facility adjacent to the highway where it could grind up the material and pump it directly into the plant.

To determine the best option for the overland pipeline and design the facility, Traxys enlisted the services of global consulting and engineering company Pöyry. The engineering firm designed a 20-inch diameter pipeline supported from H-frame structures approximately 30 feet above ground. The facility will utilize a dry blow line equipped with 700 horsepower pressure pumps to transport the material from the access drop off point to the power plant, a distance of 2700 feet.

Engineers considered a variety of alternatives for the distribution power needed to run the system. A key challenge was providing the 14 to 15 feet of clearance necessary to protect employees who might be working near the wire while maintaining the pipeline. The powerful blow line pump motor would limit the amount of material plugging the line, but periodic maintenance, cleaning, and servicing would still be necessary.

The route includes a 30-foot river crossing, so underground wiring was not deemed feasible. One alternative was using a 3-conductor metal clad (MC) cable on messenger wire. Another option was using a spacer cable system, manufactured by Hendrix Aerial Cable & Systems.

Engineers from Pöyry's Appleton, WI office had experience with utilities that installed spacer cable to improve the reliability and power quality of primary distribution systems while making them more resistant to storm damage.

Spacer cable is a messenger supported three layer cable construction system in a close triangular configuration.  The high-strength Alumweld-Aluminum (AWA) messenger cable is the primary mechanical support member for the system and also can serve as both system neutral and lightning shield. Clipped to the messenger wire is a series of high density polyethylene spacers, which support, separate and clamp the phase conductors in a compact, triangular configuration. The phase conductor's high impulse strength dielectric covering allow reduced NESC phase spacing which provides a significantly reduced configuration when compared to standard, bare wire construction.

According to Ted Gardner, sales engineer for Hendrix Wire & Cable, LWEC's engineers originally decided to look at  the spacer cable system because its required clearances were much lower, due to the dielectric covering on the spacer cable conductor.

However, as Gardner explains, "Spacer cable conductor has a small surface charge to it, so regulations require that we treat it like bare wire in terms of required clearances if the conductor is to be accessible by maintenance personnel."

LWEC's engineers then thought they would have to use aerial bundle cable (ABC), a relatively expensive cable in which all three (3) conductors are together in single, large cable housing. ABC cable is used primarily in areas where workers are very close to cable, for example in mining or tunnels.

Source: L'Anse Warden Electric Company