Project Description
In 2013, Cheyenne Light, Fuel and Power Transmission, a subsidiary of Black Hills Energy, constructed a new 115-kV line on the outskirts of Cheyenne, Wyoming, to serve a growing part of town. The initial installation was a double-circuit, 115-kV steel monopole construction using 795-kcmil ACSR Tern rated at 953 amps (Figure 25). Shortly after installation was complete, one of the circuits saw large and unexpected load increases due to a growing end user. By 2018, this circuit was reaching capacity. Because the structures were new, methods to increase capacity while preserving the existing structures were evaluated and a decision was made to reconductor.
Figure 25. Double-circuit line and existing substation
Options Considered and Justification for HTLS
Initially, other ACSR conductors such as 1272-kcmil ACSR Bittern were considered; however, the structures were not capable of the increased mechanical loading from the larger and heavier conductor. ACSS conductors were then considered but would have experienced excessive sag at high temperatures, making that technology unsuitable. Another Black Hills Energy utility had previously used the 477 Hawk ACCC on a reconductoring project and, therefore, was comfortable with the performance of this composite core product for use in Cheyenne. To meet the projected load growth, a 1026-kcmil Drake ACCC was considered. After substation upgrades, this conductor would be able to carry 1843 amps, or an increase of 94% in capacity over the existing conductor, without replacing or changing any of the existing structures.
Installation Review
To maximize ampacity on the route, the high-emissivity ceramic E3X coating was also added to the ACCC conductor (Figure 26). This combination of a composite core, ACCC, and the high-emissivity E3X provided a potential 2057 amps of capacity, or a 116% increase from the existing ACSR line. Reconductoring with an ACCC/E3X conductor allowed Black Hills to maximize the use of the existing infrastructure, saving cost and installation time while allowing for maximum future growth on a line with a fast-growing end user.
Figure 26. ACCC/E3X conductor coursing through a bull wheel
Additionally, because only one circuit of a double-circuit line was upgraded, the installation will be a great test location to observe galloping differences because it is an east–west line in an extremely high-wind area. The lines are readily observable, and other ACSR lines in the area have had galloping problems. The E3X coating has some promising ice phobic characteristics, which should reduce ice buildup and reduce galloping in the future. Black Hills will be monitoring performance because it is always looking for the best practice designs to mitigate galloping to reduce maintenance costs and outage numbers.