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Port of Seattle

The Port of Seattle is a leader in moving people and cargo across the country and around the world. With facilities and property ranging in scope from a half-acre park to one of the largest airports and container terminals on the West Coast, the Port maximizes the public assets in their portfolio with an eye toward best uses and environmental sustainability.


POS Alternate Utility Facility_1
POS Alternate Utility Facility_2
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Implemented backup power to SeaTac Airport designed to operate despite single device failures, earthquakes, and lightning events
1.2-acre site with ten 3 MW Cummins generators, a 16-bay switchgear building, a load bank, and a control building
Design of a parallel 1,800 A duct bank and an eight-bay 12.47 kV ATS switchgear building for soft transition
Centralized control system with redundant PLCs, Ethernet network, and Modbus monitoring
Voted by Mortenson as 2017 Design Partner of the Year for Excellence in Preconstruction 

Project Description

The Alternate Utility Facility (AUF) project's primary focus was to provide a backup power source for SeaTac Airport in the event the 115KV utility feed is disrupted. Special consideration was given to ensure the facility could operate if any single device was to fail. The facility was also built to withstand major earthquakes and lightning events. The AUF project was a Design Build project with Mortenson being the primary contractor on the project. 

Casne developed a master PLC program controlling the AUF site & ATS Switchgear Building, monitoring PSE feeds, managing generators, ensuring fast transfers, and reacting to faults. It includes an HMI for manual override, diagnostics, event reporting, and allows for generator load testing. Load tests stop if PSE feeds are lost.

The 1.2-acre site contains ten 3 MW generators, a 16-bay switchgear, a 3 MW load bank, and a control building. A redundant control system allows monitoring and control of all equipment. AUF can transition loads within 100 msec and is built to withstand earthquakes and lightning events. The project completed in 2018, providing a reliable, efficient, and resilient backup power facility.