Britain's National Grid requests extra generation after plant outages

(Adds National Grid comment, power price)

May 10 (Reuters) - Multiple power plant outages on Monday evening prompted British energy system operator National Grid (LSE: NG.L - news) to ask for 1,500 megawatts (MW) of extra power capacity to be brought online.

The operator notified the market that the so-called system margin, a safety cushion between demand and available supply, was expected to fall below adequate levels from 1800 to 2030 GMT.

British day-ahead power prices rose by 4.5 percent to 37.30 pence per megawatt-hour (MWh) on Tuesdy morning.

"The notification of inadequate system margin (NISM) was a result of combination of multiple plant breakdowns," a National Grid spokeswoman said, declining to name the plants.

"The market responded to the notice and the NISM was cancelled at 2015 GMT," she added.

National Grid has said that notifications of inadequate system margin do not mean there is any immediate risk of supply disruption or blackouts but are aimed at ensuring a sufficient reserve buffer. (Reporting by Nerijus Adomaitis; Editing by David Goodman)