On 20/05/18 22:25, Steve Walker wrote:
On 20/05/2018 21:31, Vir Campestris wrote:
On 20/05/2018 19:14, Steve Walker wrote:
I don't know about power station generators, but when I was involved
in testing a couple of 3-phase, 60Hz, 11kV, 24MW generator sets for
North-sea oil rigs, they consisted of an RB211, exhausing into a
DR-61 turbine and direct driving (according to the manufacturer's
nameplate) a "Brush AC Generator".

Oooh an expert

Not much of one.

I always assumed that in those kind of tasks they just used the
turbine that normally drives the fan (which I assume isn't there!) Why
not? Doesn't it extract enough power?

That's basically it.

From memory (this was nearly 25 years ago), an RB211 (for aircraft)
actually has three compressor stages (low, medium and high pressure), on
three co-axial shafts, driven by three turbines. The turbines are sized
to power the appropriate compressor stage and you get a lot of hot, fast
moving exhaust. The reaction to the exhaust escaping backwards is to
push the engine forwards.

An RB211 (for industrial use) only has two compressor stages (medium and
high pressure), on two co-axial shafts, driven by two turbines -
probably because the air at ground level is dense and the first stage is
redundant. Again, the turbines are sized to power the appropriate
compressor stage and you get a lot of hot, fast moving exhaust. In this
use, it is actually termed a gas generator (or was by the company I
worked for) and you don't want the GG to move. Instead it is bolted down
and the exhaust is directed into a power-turbine, which is driven by the
gas, before exhausting to a heat recovery plant. The power-turbine
drives whatever load you have attached.

There is no direct connection between the load and the GG. It is
impressive how well the control system (Woodward governor on those sets)
ramped up the fuel control to bring the power turbine up to running
speed with only a tiny overshoot and then settled to constant speed.
Although slamming a 10MW motor online REALLY made the revs/frequency
drop for a short while!

It amused me at the time that the Rolls-Royce manuals referred to
allowing the engine to cool before turning it off, by "taxiing for 3
minutes."

SteveW

A bog standard open cycle gas turbine then..




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