HARTFORD, Conn. (AP) — United Illuminating shut down three power substations in Bridgeport Monday night in advance of a high tide that was expected to cause unprecedented flooding at the facilities, which were built to withstand a 100-year flood.

UI vice president Tony Marone said the action was taken to prevent catastrophic damage that would occur if the sea water reached energized equipment.

He said workers were using pumps, sandbags and other methods to try and keep the water out of the control rooms.

‘‘If we are successful, then it will allow us to repower those substations in a much, much quicker fashion,’’ he said.

About 52,000 customers, including about 47,000 in Bridgeport, lost power as a result of that move.

The company also continued to monitor a substation in New Haven that was being threatened by the tide, he said.

Connecticut Light & Power says its workers spent the day erecting a 6-foot tall concrete wall around a substation in Stamford to protect it from the water, and it was monitoring the potential for flooding at a substation in Branford.

About 353,000 CL&P customers were without power as of 7:30 p.m. UI was reporting 47,000 outages before taking the substations offline.

Most of those outages were wind- and not water-related, company officials said.

The companies say crews were out restoring electricity in areas where the wind would allow that work to occur. Crews were not going out in areas of the state where wind speeds were about 40 mph.

Bill Quinlan, a senior vice president at Connecticut Light & Power, said his company had about 400 of its own line crews and 1,060 contractors ready to respond to the storm Monday. He said the utility is soliciting about another 1,000 outside line workers to help with what it expects will be a major restoration effort.