I have power lines no far from my loft and its always been a problem for me, I loose a couple of birds every year and If the wind blows a certain way or its over 10/15 mph they stay in.
I have had the electric people out several times and they are covered in swinging target type of dangling things all along the wires every 3/4 feet but they still hit them if the weathers windy, in the summer I only let half the youngsters out at time, as the less there is flying about the less they seem to hit them. I would ask them to put them on yours before you start as it takes weeks for them to come out but Good luck.