Many residents and businesses within the city of Madison and the surrounding rural areas were without power for around 20 minutes Wednesday afternoon due to a problem with an East River Electric substation.  Jim Edwards of East River Electric said the problem was at a substation near Montrose that affects the city of Madison and some surrounding rural areas.  Edwards said that the problem affected one of the city's substations causing part of the city to lose power.  He said the problem has been isolated and power has been restored.