[Arran]

 They had some weird stuff back then that doesn't really exist anymore that would cause all sort of interference, like diathermy machines, street cars, etc. They also did used to use power lines for communications purposes more so then now, although I think they still do for fire alarms. I think you could leave any or all of them out and it would not make any difference, but it's curious how they added them on each leg of the high voltage winding, maybe they were trying to create an LC circuit for filtering higher frequency noise that might get through?
Regards
Arran