The Corps of Engineers reports inadequate components, apparent gaps in a protective relay system, and operator error contributed to fire damage at the 100-MW Detroit Dam powerhouse on Oregon’s North Santiam River.
The Corps previously determined the cause of the electrical fire to be phase-to-phase arcing in Unit 2 bus works, ancillary equipment used for the electrical connection from the generator to the step-up-transformer. (HNN 6/28/07)
A Corps board assigned to investigate the June 19 fire added that a contractor installed surge arrestors that were different than those approved and used under-rated cable. The Corps’ quality control and quality assurance process did not discover the situation before the fire.
Additionally, there was no ability to trip equipment quickly. The power to a critical protective relay was tagged out, removing a level of protection. There also appeared to be gaps in the plant relay protection system, the board said. Drawings were inaccurate and could have contributed to confusion and a lack of understanding.
As for operator error, a breaker was closed manually without proper diagnosis of a problem, the board said.
Corps estimates repairs could total $9 million
At one time, the Corps estimated costs to replace damaged equipment could total more than $4 million. However, the Corps now says estimates for returning the project to service, including clean up, interim repairs, and capital improvements to switchgear range from $7 million to $9 million.
In-house Corps teams made interim repairs. The Corps said contractors named to return the project to service include Shaw Inc., for clean up, and National Electric Coil, which is to rewind Unit 2. The government also awarded a contract to Olssen Electric to perform reliability upgrades.
The Corps said it plans to return Unit 1 to service in February 2008. Unit 2 will be returned to service sometime during summer 2008, after the rewind.
Corps returns 20-MW Big Cliff to service
The Corps said it returned the 20-MW Big Cliff powerhouse to service in mid-September on the North Santiam about three miles downstream from the Detroit powerhouse.
Although Big Cliff was not damaged in the fire, its systems are connected to the Detroit powerhouse, which in turn is connected to a Bonneville Power Administration substation.
Detroit and Big Cliff dams are among 13 multi-purpose dams operated by the Corps in the Willamette Valley. Detroit’s 463-foot-tall, 1,523-foot-long concrete gravity structure stores water for generation, flood control, irrigation, recreation, navigation, and water quality improvement.