Waterford - The Millstone 3 power plant automatically shut down Saturday night when an electrical fault was detected in the nuclear station's main generator.

Neil Sheehan, a spokesman for the Nuclear Regulatory Commission, said the reactor tripped, according to design, and that all safety systems were fully functional.

"Our resident inspectors at Millstone responded to the site and observed actions taken by the personnel to place the plant in a safe shutdown condition," Sheehan said in an e-mail. "They will also monitor (Millstone owner) Dominion's troubleshooting efforts with respect to the generator."

The NRC started inspecting Unit 3's reactor last week after trapped gas was discovered during a routine plant shutdown in the fall. The special inspection had been continuing just as the problem in Millstone 3's main generator came to light.

The two problems do not appear to be related.

Sheehan said the plant has been dealing with the problem by releasing steam to reduce residual decay heat from the power-production process.

He said the steam is from the plant's non-nuclear section.

The Millstone 3 shutdown occurred at 10:53 p.m. Saturday "due to an apparent ground (electrical fault)," Sheehan said.

Millstone 2, he said, remains at full power.