MONTICELLO -- Xcel Energy officials say the Monticello Nuclear Generating Plant shut down safely this afternoon after a transformer lock-out.

The company says that lockout briefly interrupted non-safety-related power from the grid to part of the site.

Xcel's Mary Sandok says operators are still investigating what caused the transformer lockout.

Sandok says all safety systems reacted to the lockout as they should and the situated posed no danger to either workers or the public.

Sandok says the shutdown was not expected to be lengthy.

The Monticello plant generates enough electricity to power around a half-million homes.