Donnells Powerhouse is a single unit hydroelectric facility located in Tuolumne County, California. The powerhouse was originally constructed and commissioned in the late 1950’s. As with any aging powerhouse facility, the decision to replace the existing generator step-up transformer (GSU) bank was based on the associated risks of extended forced outages caused from a major transformer failure, and in consideration of the end of life assessment performed on the existing GSU bank at this critical 90 MW facility.
Additional project constraints included a forest service road with limited access and a weight-restricted bridge used to gain access to the powerhouse facility.
SAGE was hired to provide electrical engineering services for transformer replacement specifications, bid evaluations, protective relay design, and system integration.
Upon evaluation of alternative design approaches, vendor bid submittals, and recommendations by SAGE’s electrical engineering team, our client elected to maintain the original single phase bank design approach. SAGE’s design provided substantial construction and integration cost savings by utilizing the existing bus and transformer oil containment system. The GSU upgrade included enhanced transformer protective relaying and coordinated settings through implementation of redundant microprocessor relays.
Additionally, SAGE provided construction and commissioning support including test / startup plan development, and utility witness testing and commissioning for the transformer and protective relay replacement project.