Highlander 500kV Solar Substation

Mortenson was the engineering, procurement, and construction partner for the Highlander 500kV substation, transmission line, and distribution line project, in addition to and in support of the Spotsylvania 617 MWdc solar generation facility.

The electrical infrastructure for the substation included three 500kV 295MVA transformers, twelve circuits with thirteen feeder riser bays, two 500kV breakers, thirteen 34.5kV breakers, and eight 15 MVAR capacitor banks for a total of 120 MVAR reactive power compensation. Mortenson self-performed the substation, less foundations, bus welding, fiber terminations, and NETA testing, and was also the Engineer of Record for the project.

The design incorporated metering for each individual circuit along with separating this across four different project entities.

The substation protection was designed to follow all pertinent NERC PRC requirements. The setup consisted of relays located in the control enclosure paired with merging units located at the equipment. The substation does not use the traditional hard-wired lockouts; instead, all lock-out relays exist electronically within the appropriate protective relays.

Mortenson coordinated closely with our trade partner to set up the Power Management (SCADA) system for the site, which allows for remote monitoring of all pertinent information within the substation and solar array.

As the substation and solar array were being prepared to be brought online, Mortenson coordinated outages with the local utility at the 500kV level (off-site) and enacted our Project Energization Plan to bring up the substation and array safely and with minimal issues.

Commissioning of the facility included testing of all equipment within the substation, end-to-end testing with the local utility along with point-to-point check-out and SCADA points list prior to energization. Post-energization commissioning included proofing of all protective relays and equipment, along with equipment training and presentation of final system manuals.

The transmission line included 1,500 feet of 500kV custom steel monopole structures to the point of interconnect, and the distribution line required 54,000 feet of wood monopole structures for the solar field itself. 

Over the course of the project, the team faced handfuls of hurdles, including a lengthy county permit approval process and unpredictable weather. When the COVID-19 pandemic struck, the team banded together and implemented measures and tactics to ensure the safety of all workers on site.