The unit shut down by a malfunction at Connecticut’s nuclear power plant is generating electricity again, a spokesman said Thursday. Millstone Power Station and regulators said Unit 3 shut off automatically on Aug. 9 when an instrument failure caused a drop in the level of water used to cool the reactor core. The 1,200-megawatt unit was reconnected to the regional power grid Wednesday afternoon, spokesman Ken Holt said. He said it was at about 80 percent power on Thursday morning and was expected to reach full power within about a day. The problem was traced to a faulty power distribution panel, which has since been reconfigured, Holt said.