Background
In 2009, Nevada Power (doing business as NV Energy) identified a 220-kV transmission line
that required an increase in transfer capacity from its current 300 amps using a 2/0 Cu conductor to a minimum of 1000 amps. Traditionally, NV would use a 954 ACSR conductor for this line capacity level, but the wood H-frame line built in 1952 could not support the increased mechanical loading of a 954 ACSR conductor. The typical upgrade would require a complete rebuild of the 13-mi (21-km) -long line.
Options Considered
Because the line was built in the 1950s, the area around the line had built up with moderate and higher priced residential areas and several golf courses. NV planning and transmission engineers speculated that most of the line would have to be built with an underground replacement line to avoid permitting conflicts with the existing route for a complete rebuild. As an alternative, NV looked at applying an advanced conductor that would offer increased capacity for a similar or slightly larger sized conductor to replace the existing 2/0 Cu. After reviewing different options, NV decided on a 431-kcmil Linnet ACCC conductor. The Linnet was slightly larger in diameter than the Cu but approximately the same weight. The existing H-frame structures could carry the new conductor while providing desired clearances and meeting the 1000-amp capacity requirement.
A major factor justifying NV’s first ACCC application was that, by retaining the original structures, it could permit the work as a maintenance project and avoid lengthy permitting and major siting issues. In the end, approximately one-third of the wood poles were replaced due to their physical condition and all cross arms were replaced. The final project solution cost approximately $4 million compared to the $8 million rebuild alternative, not including the time and costs associated with more intense permitting and approval requirements associated with their standard 1000-amp configuration.
Construction and In-Service Follow-Up
Construction proceeded routinely following some initial training on handling the ACCC conductor, relative to its fully annealed aluminum strands, the unconstrained core, and collate-based connectors applied for ACCC dead-end and splice fittings.
While the line has been in service, it has experienced two significant environmental events. In 2010, a 100-mph windstorm blew across the area the line was located in. Several structures experienced significant walk-out pole movement due to transverse loading on H-frames. Later, in 2012, a firestorm swept the area, destroying 27 residences in the area and impacting four structures, two of which were completely burned to the ground. Following an inspection of the conductor laying on the ground, it was determined that the conductor was sound, and it was lifted back into suspension assemblies on the rebuilt structures. In both cases, the ACCC conductor survived the events without deterioration or damage. NV’s experience with their ACCC application warranted additional reconductoring projects with ACCC.