Mike,

It is - 350 kV and + 270 kV.

So the potential difference is 620 kV dc.

I am pretty sure that the negative value is higher than the positive value.
it has something to do with the semiconductors used, although some of the ASEA rectifiers have mercury in them too.

if i find that link i will post it on ECN.

The product of rotation, excitation and flux produces electricty.