Hi
are you saying that the generator has a vaccuum to reduce windage??
If so is it "rising" towrds 101kpa (a) when the unit is static and or rotating. From this we are going to mention rotating seals and gasketing and cable entries etc etc etc
I have never serviced an alternator which uses vaccuum. BUt we have dealt with a lot of chemical plants which do?
I am confused when you say protection? surely this could be from the simple pressure switch to an industrial type pressure transmitter to the control room.
Do you have a vaccuum pump on this service? If so youve got a big leak. A common tecnique in chemical plants to trace down the leaks is to +ve pressure the unit say +20 kpa(g) and the use snoop or some other suitable leak detector to spot the problem.
now i've shot my mouth off I'll sit back to see what I missed here
Let us know how it goes
Don