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Grand Coulee Generator Step-Up Transformer Evaluation
Bonneville Power Administration

Portland, Oregon


The Left and Right powerhouses at Grand Coulee contain eighteen 100-MW generating units. Each generator feeds three single-phase step-up transformers, ranging in age from 16 to 62 years. Two spare phases are kept on site. BIS staff developed an optimized strategy for purchasing spares or replacing transformers by balancing the risk of failure against the capital cost of replacement.

The results showed that the optimal solution for Bonneville Power Administration was to keep three spare phases as the benefit of the spares strategy was much higher than any replacement program. BPA was advised to adopt a do-nothing strategy once all the spares were in place, ruling out the need for an expensive replacement program.

Date Completed: 2002

Optimized number of spare transformers. Defined process to identify projects and optimized them economically.
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