The Big Sky Substation is a 260 MW, 220kV/34.5 kV, 6 transformer bay substation that connects to Southern California Edison’s (SCE) Antelope substation over a 0.2 mile 220 kV generation tie transmission line (gen tie). The gen tie line and 220 kV substation facilities are engineered for a final planned buildout of 930 MW. The substation is arranged as a single 220 kV strain bus fed by an incoming line breaker. Each 220 kV to 34.5 kV generation step up power transformer is radially tapped off of the 220 kV bus.

In 2017, an additional two 20 MW transformer bays were added to the existing station to bring the total station generation up to 300 MW. This is referred to as “Expansion Phase 1.” In 2018, a 5 mile 220 kV underground transmission line was tapped off of the Big Sky Substation bus and a new 225 MW 230 kv/34.5 kV substation was built to the north. This is referred to as the “Antelope Expansion.” DEA (formerly TriAxis, a Division of David Evans and Associates) is the engineer of record and designer for both of these expansions.

DEA was responsible for the design of the following components:

• Substation preliminary design, long lead equipment specifications, and site development assistance to owner, iterations to accommodate need for an expandable station.
• Substation design, engineer of record, and construction/commissioning support for the 260 MW substation. Teamed with DISTRAN who provided final outdoor electrical, foundations, lightning protection, lighting, and steel design.
• 2 mile generation tie transmission line, diverse and redundant fiber communications paths (OPGW and ADSS), and pull-offs into the project substation
• 5 kV collector system studies including arc-flash, short circuit, power flow, inverter skid grounding, and coordination (set of studies performed for each of the 13 34.5 kV collector circuits).

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