Mill Electrical Substation Upgrade

One portion of the project addressed the review of the entire 138 kilovolt (kV) above-grade upgrade design and the #2-69 kV bus side of the tie gas circuit breaker ‘H’. Also, we designed five 69 kV gas circuit breakers and all the wiring and associated schematic drawings that illustrate the protection and control schemes, layout, and assembly of equipment and protection devices. This work included the design, wiring, and protection for the 138/69 kV transformer, as well as the 69 kV station service transformer.

Additionally, the design incorporated the ability to add two 138/12 kV transformers to accommodate future distribution feeders, which will enable electricity to make its way safely from power stations to homes, businesses, and community facilities. For storm hardening, redundancy, and reliability, another 138/69 kV transformer was incorporated. And, as a result of the forward-thinking design for the 138 kV ring bus, the new transformers were installed and constructed without a system outage at the station.

• Installed an 8-position, 138 kV ring bus for increased reliability.
• Removed all aged and oil based circuit breakers.
• Installed a new 24-foot by 44-foot control enclosure to provide an additional level of protection for sensitive electronic equipment.
• Upgraded to modern microprocessor-based relays to improve performance, accuracy, and longevity of substation assets.
• Changed the existing end-grounded system to center-grounded, while maintaining a small end-grounded distribution service to accommodate existing end-grounded devices.

• Optimal configuration to strengthen reliability of the substation.
• Improved service reliability for customers.
• Electricity supplies for future growth.