A 56-year-old South Boston woman fell after trying to ride her motorized wheelchair up the escalator at a subway station last Friday but was not seriously injured, the MBTA said. The woman, whom officials have not identified, tumbled several times as the escalator rose out of Broadway Station at about 9:34 a.m. A man ran to her aid when he saw her flip over. He nearly tripped trying to set her upright on the moving escalator. An MBTA worker then rushed to the scene and pushed the emergency stop button. The woman was able to walk down the stairs and had no serious injuries, the MBTA said. The scene was recorded by one of the MBTA’s newer surveillance cameras. The T is installing thousands of new cameras using federal grant money.