Ability of a 100km power transmission line to radiate 50Hz EM waves?
A well designed, installed and operated 50Hz transmission line radiates very little EM waves. It’s short for that frequency, and more important the lines are arranged to cancel the fields pretty well compared to the wavelength of 50Hz (about 6000km). 

But that doesn’t mean that there are no E and B fields in the few hundred meters around the line. On that scale, the cancellation is not complete. You can detect significant fields out to a few 10’s of times the conductor spacings.  

It’s just that those are local fields, not radiating out as waves.