Open the image
Create a new black layer
Choose the Spot Healing Brush tool and be sure the Sample all layers is on
Make the brush a little bigger then the power line. Hit the beginning of the power line and with Shift selected hit the end of the power line to make it straight. If the line are not straight just go over the power lines to remove them.
You also can do it on a copy of the background layer and in combination with the Clone tool (S).
Do it step for step and sometimes go back.