Chugach Electric Association restarted the rebuilt turbines at its Cooper Lake Hydroelectric Project this spring.
However, one of two turbines at the site has been shut down since July 30, when a metal cooling fin broke on one of the plant's electric generators, said Phil Steyer, utility spokesperson.
Flying metal from the cooling fin damaged the copper windings on the generator. Since then, the plant has been operating at about half-power.
Chugach overhauled the hydroelectric plant last winter in a project expected to cost about $6 million.
During the overhaul, workers replaced 1950s controls and made improvements expected to in-crease the plant's capacity from 17.2 to 19.4 megawatts. It sent the plant's two generators to a General Electric facility in Utah to be rewound.
Environmental work following the discovery of PCB contamination at the plant pushed the cost of the overhaul to about $10 million.
Steyer said Chugach still is investigating the extent of the damage. It is not clear whether the generator will have to be rewound or when Chugach will be able to restart the second turbine.
Chugach has hired forensic engineers to determine the cause of the failure, he said.
"This isn't a part that was replaced, but there is a question of whether in the course of the work, someone should have inspected these parts," he said.
There also is a question of whether the cooling fin could have been damaged during the overhaul.
"The question of who is at fault and who pays has yet to be resolved," Steyer said.
Licensed in 1957 and commissioned in 1960, the Cooper Lake project now comprises a small fraction of Chugach Electric's generating capacity, which totals more than 500 megawatts.
Chugach produces most of its power from natural gas-fired turbines at Beluga Power Plant in western Cook Inlet.
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