A fire at a Moscow power station -- the second at the plant in two weeks -- caused huge traffic jams in the center Tuesday as electricity supplies to some of the city's trolleybuses were cut off.Trolleybuses came to a sudden halt on the Garden Ring and on Ulitsa Tverskaya, blocking two of the city's major thoroughfares, when fire brigades ordered a nearby hydroelectric power station to be switched off. Andrei Malozin, spokesman for the Moscow fire department, said the fire brigades entered the plant to check reports of heavy smoke in an underground cable tunnel.Firemen arrived in large numbers because they feared a repeat of a major fire at the same plant, the GES-1 hydroelectric power station across the river from the Rossiya Hotel, two weeks ago.According to Malozin, the insulation around the electric cables had melted, causing thick smoke but posing little hazard to the plant itself. Sloppy repairs after the first fire may have caused the incident, he said.