In January, MidAmerican Energy (MidAmerica; Des Moines, Iowa, U.S.) began construction on a 201-km (125-mile) transmission line and substation in Grimes, Iowa. Work will include construction of a substation in Grimes, near Des Moines, and a 345-kV line from MidAmerica’s Council Bluffs Energy Center (CBEC) to the Grimes Substation.

The new line will be a 345/345-kV double-circuit bundle T2 conductor (556 KCM) on the first 24 km (15 miles), 345/161-kV double-circuit with a T2 bundle on the 345-kV side and single T2 conductor on the 161-kV side for the remaining 177 km (110 miles). The average structure height will be around 42 m (140 ft) and will be composed of single-shaft steel poles set on anchor bolt foundations. The assemblies will be made of V-string polymers on steel arms.

The L.E. Myers Co., a subsidiary of MYR Group (Rolling Meadows, Illinois, U.S.), was awarded the engineer procure construct contract. Stanley Consulting was retained to perform line design.

Steel Structure

The design calls for steel poles and replacement of most existing wooden H-frame supports with single steel poles. Early estimates are that 27 million lb of weathering steel poles will be required for the job. L.E. Myers, which awarded the tubular contract to Thomas & Betts/Meyer, will manufacture the structures at its facility in Hager City, Wisconsin, U.S., located about 482 km (300 miles) from the line construction project. The lower shipping costs and delivery times have offset the concern for rising steel prices.

Route span and structure configuration includes an average spacing of 274 to 414 km (900 to 1360 ft) in Pottawattamie County and 320 m (1050 ft) spacing in the other affected counties. Near the CBEC, the new line will be mounted on four existing steel lattice towers currently carrying a single 345-kV circuit for about a half mile. For the Pottawattamie County section, where a 345-kV circuit will be added to existing steel towers that are 30-plus years old and carry existing conductor, some refurbishing might be required to ensure that the system is structurally sound and capable of supporting the weight of a second set of 345-kV circuit conductors.

Hamby-Young (Aurora, Ohio, U.S.) is in charge of materials packaging, which includes 6.7-m (22-ft) steel arms and V-connected suspension insulators to support the added 345-kV conductor, protective lightning protective shield wire mounted on 4.3-m (14-ft) steel arms at the top of the poles. Fiber-optic cable also will be mounted on the steel arms to carry communications for monitoring grid performance. During the reconstruction phase, L.E. Myers crews intend to keep the existing 161- and 345-kV circuits in operation when possible to minimize outages.

The 196-km (122-mile) project is the result of a study conducted by MidAmerica, Omaha Public Power District, the Nebraska Public Power District and other joint-owners of the new Council Bluffs Energy Center. It will enhance the reliability of MidAmerica’s transmission network and relieve constraints in and around the utility’s service territory. It will also serve as an outflow connection from the new 790-MW generation facility being built in Council Bluffs.