Maciek.
I can not remember for 100% but here is my guess. There are two adjusting shafts on each main motor/generator. They are situated just above the stators and I think your may see a greasecup on the shaft casing, this, I believe, is wormwheel drive connected to the shaft. By putting a handle or wheel on the shaft you are able to turn it thereby the stators and adjusting the magnetic field of the motors/generators, I don`t think we did this often.. Simon has a wonderful drawing where he has shown the system, I take the liberty to show his picture to explain what I mean.
Tore