Mayfair Substation
2026 Engineering Excellence State Finalist
Entering Firm: HDR
Client: Xcel Energy
Projected economic growth in Onalaska hinged on infrastructure being able to meet the needs of two expanding companies. The bottleneck was electricity. An old substation was unable to provide the extra demand needed and an increased the risk of system failure for the entire community.
Engineers created a robust electrical system to serve growing needs and keep power flowing in an emergency.
HDR designed a new transformer with new technology that exceeds demand and reduces stress on the system. A key feature of the project is its unique tandem bus design. The rareness of the tandem bus design meant the team could not draw on past substation designs.
Although complex to engineer and implement, this configuration allows the client to reroute power quickly in the event of a failure or surge. This setup offers more flexibility and maximizes reliability which was essential to customers including the two expanding companies.
Replacing transformers while keeping at least two online required a carefully orchestrated ten-phase outage sequence. After installing the third transformer, power was gradually shifted to allow the older units to be de-energized and replaced without interrupting service.
Completed on schedule and within budget, the upgraded substation now supports major economic expansion while strengthening capacity for future residential growth.