Dry edges on sponge cake, nest 2 sheet pans for insulation?
There are a couple of things that can lead to uneven heating in an electric oven. Here a couple of things that can help.


Let the oven 'thoroughly' preheat. Are you putting the cake in before or just as the oven preheats? Let the oven sit for a good 5 minutes after it has reached the desired baking temp.
Keep the oven door closed until the expected baking time has been reached. Each time the door is open a significant amount of heat escapes, causing the elements to come back on for a longer period, this will cause the heat to circulate in an uneven pattern.
place either a pizza stone or another baking sheet on a rack above the cake (with enough room for the cake to rise). If the broiler element is coming on the direct heat might be causing the dry center (note: if you had a gas oven then I would put the stone a rack below the cake.)
finally, lower the temperature 25°F and extend the baking time.