Big Sky Substation

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.

TriAxis 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).

In 2017, an additional two 20 MW transformer bays are being 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 is being tapped off of the Big Sky Substation bus and a new 225 MW 230 kv/34.5 kV substation is being built to the north.  This is referred to as the “Antelope Expansion.”  TriAxis is the engineer of record and designer for both of these expansions.

Completion Date:
Big Sky Substation: July 2016
Expansion Phase 1: September 2017
Antelope Expansion: Late 2018

Design work for which TriAxis was responsible:  100%


Junction City Substation

The substation design was for Blachly Lane Electric Cooperative. This Distribution Station is feed by a 115kV line tap to an A-Frame Structure. The station includes a high-side 115-kV group operated vertical break switch, 115-kV circuit switcher, 115-12.47Y/7.2KV 30/40/50MVA transformer, three single-phase regulators, a 15kV circuit breaker, side break group operated 15-kV switch, and four feeder bays with 15kV circuit breakers with expansion capacity for four additional. TriAxis was responsible for: 

  • Site grading design
  • Yard layout design with consideration for future expansion
  • Physical substation design including the feeder rack bays
  • Structural steel concepts
  • Control house conceptual layout
  • Relay cabinet design
  • Protection and control schematics. 

TriAxis design responsibility: 100% 

Project completion date:  2017


Hinshaw Substation

The Uinta County Wind Project was developed by FPL Energy for the installation of eighty 1.8‑MW Vestas-America V80 wind turbine generators in southwest Wyoming.  The 6‑feeder underground collection system was connected to a 90/120/150‑MVA, 34.5‑kV to 138‑kV, step-up transformer through 34.5‑kV metal-clad switchgear.  Eight 4200‑kVAr capacitor banks were provided for reactive power support.  The 138‑kV power was delivered to a new three-position ring bus switching station (fourth position future) to interconnect the project to an existing PacifiCorp 138‑kV transmission line. A new fiber optic communication line was installed on the PacifiCorp transmission line for metering and system protection.

TriAxis performed the following design tasks under contract to the lead electrical contractor:

  • Hinshaw Substation: step-up substation design including layout, foundations,
    bus work, metering and the control
    wiring interface.
  • Long Hollow Switchyard: four-position 138-kV ring bus switching station including interconnection with the PacifiCorp control and communication systems.
  • Fiber Optic Cable (OPGW) design for
    the existing PacifiCorp 138-kV trans­mission line.
  • 6-MVAr medium-voltage capacitor bank; reactive power control system; protective relay settings; communication system installation support; and engineering services during construction.