On Wed, 30 May 2018 14:24:40 +0100, tony sayer wrote:

In article , The Other Mike
scribeth thus
K rectified when fitted to a vehicle.

In a power station on the end of the alternator opposite from the turbine you'll
find a DC field excitation generator / pilot exciter that does have a
commutator.

I suppose thats so it can start up by itself under shudder! Black Start
conditions;?..

Not particularly, by the point you need excitation current at least for a coal
/oil / nuclear station you will have been heating the boiler for several hours
and the turbine and generator will be at or around full speed and getting ready
for synchronisation and load.

For a black start the DC supplies (from batteries) are used to start either
diesel generators or distillate fuelled gas turbines. That powers the AC
station bus supplies usually at 11kV or 3.3kV, with transformers for 415v and
lower supplies. From that point you can operate everything on site such as fans
pumps and valves etc.

In normal operation with a live grid the site would take a station transformer
backfeed to power everything until the main generator comes on load at which
point each individual generator transformer HV side (at 400 or 275kV) then feeds
a unit transformer that supplies 11kV to a AC bus for that specific unit. The
connection between the common station supply and unit supply is then severed.

There are some variations on this standard configuration at nuclear sites


But if you think that's dodgy they fill the stator with water and circulate
hydrogen in the gap between the stator and rotor to keep it cool.

Why Hydrogen?...

To cool the rotor and reduce windage losses compared to air cooling

Most large (as in 60MW+) power station generators from the late 50's onwards are
hydrogen and water cooled.

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