On 02/05/13 23:14, Andy Champ wrote:
On 02/05/2013 11:54, The Other Mike wrote:
The voltage at the generator terminals is for all practical purposes
(at least
in the context of this discussion) held at a constant level
regardless of load,
as is everything across the super grid until the first transformer
that has tap
changers.

Voltage to consumers can be reduced without the generators changing
their own
terminal voltage. It happens many times a day as load changes (mainly
industrial
load)

During the day a transformer may be on tap x of 20, at night on tap y.
During ALL this period the generator is at a constant voltage (around
15kV, the
400kV grid system is at 400kV, the 275kV grid system at 275kV and the
132kV grid
system at 132kV Below that distribution voltage level of 132kV the
voltage on
all the lower voltage grids can vary and can be reduced in a number
of stages to
lower demand whilst keeping voltage to the consumer within the
statutory voltage
limits of 216V - 253V. This is an existing control regime that has
existed for
half a century in the UK.

It doesn't matter if the load on the grid is 30GW 50GW or 60GW, wind
turbines
are swinging output up and down like a whores drawers, the frequency
is low or
high, the voltage at the generator terminals will*always* be
controlled towards
a predefined setpoint defined by the manufacturer of the generator
maybe 50
years ago.

http://books.google.co.uk/books?id=L7o4TitajRIC&pg=PA11&dq=automatic+voltage +regulator&hl=en&sa=X&ei=TjGCUZ_FDoXy7Abtp4DoDQ&ve d=0CEEQ6AEwAQ#v=onepage&q=automatic%20voltage%20re gulator&f=false



scroll to page 13

Frequency is determined by the speed of rotation. If speed of
rotation starts
dropping more steam is admitted It's very similar in response to
cruise control
on a relatively flat road.

If more steam is admitted then more fuel has to be burnt to maintain
the steam
pressure and temperature.

I have no trouble understanding how intermittency will cause stability
problems. However...

Google won't let me read enough of that book

So the fiddle with the exciter current to maintain a fixed output
voltage, regardless of load? Surely at some point they must run out
of steam...

What actually controls the grid frequency? Is it the tap changing at
the 132kV step down?

noo.


The way it goes is this. You start your powerstation and then when its
in phase with the grid, you connect it. At this point if you pull torque
off it. it will be a motor driven BY the grid, and as you increase
torque on it, it will start to phase lead the grid slightly and push
power onto it. You can control the voltage using the exciters - you
match that to the grid voltage.

If you open up the steam and push too much power all the grid speeds
up. Since voltage is both exciter current AND RPM, the voltage also
rises. so under normal loadings the load will affect voltage and
frequency together. The job of the grid controllers is to keep that
within limits. By (I think: this is where it gets hazy) running a real
time auction on prices. If the load goes up. the prices rises and
generators who want to deliver at that price open the throttles and do
so, Except intermittent renewables of course. they are outside any
market, getting more or less their FITS and ROCS and so its always
profitable for them irrespective of market price. Making life harder for
everyone else.

I am not sure what would happen if you changed excitation current on a
running jenny drastically. My gut feeling is that it would be a Very Bad
Thing, but I cant work out what would happen. It feels like the jenny
would go badly out of phase and start pushing massive currents through
itself without generating power and would go up in smoke. But I cant
quite remember the sums or pictire it.

the balancing system is interesting.

Nuclear generators have almost no incremental fuel costs at all. They
may not be profitable running at low electricity process at night, but
they dont save anything by switching off. That's more than anything is
why they run the baseload. Every other power station at some point will
say 'its cheaper NOT to burn the fuel and throttle back' that never
happens with nuclear. They can and are throttled a bit, but too much
throttling mucks up the reaction and leads to poisoning IIRC. However
one muke is cvurently on reduced power to save fuel till its next
reload, so they can do that.

At the other end of he spectrum intermittent renewables are
'irresponsible' with 'private incomes' of FITS and ROCS. SDo they will
be and are profitable irespective of market price of electricity and
they cant be turned down anyway. Just turned off altogether. So they are
always generating whatever the source will alllow as well.

Hydro is interesting. Most sites are more limited by water, than by
capacity. So they run a crafty game selling their precious water power
at the peak of demand. Day mainly. If te das however are full to
bursting, they might as well get what they can, so you see more hydro
after periods of heavy rain in offpeak times.

Coal seems to run as hard as it can, most of the time because coal is
cheaper than gas. Gas is the first to be taken off the grid when the
wind is blowing for example. One reason why renewable UK's predictions
about wind displacing coal and gas in the ratio they are on the grid,
one for one are ********. Also its a lot longer to get a coal plant up
than gas so they are generally not shut down but throttled back at night
when all the gas - or most of it - has been shut down. It looks like
some are closed over weekends though.


Gas is used sparingly because gas is expensive and gas sets are fast to
start, so in general they are off at night with just a few ticking over.
by day they are used to cover peaks because they can be ramped up and
down fast. In general wind and gas are playing in complementary fashion
in the UK, leaving coal and nuclear to cover the baseload. ..by and
large wind and solar do nothing for coal consumption but a lot for gas
usage. However its arguable as to whether this actually saves any gas
overall - the extra ramping involved in the gas probably negates any
actual reduction in the amount of electricity they generate.

returning to topic, the fact is that whereas voltage is locally
interesting and reflects the local power being drawn, and the local
impedance of the source, it doesn't really reflect overall national
demand. Frequency does. If you want a smart meter that doesn't have to
be taught anything about local conditions to modulate overall grid
demand, then you will use frequency.

But the real issue is how much load you could take off the grid anyway.
And as you will;l realise its at best 10% if that, and then only for a
few hours max.

To generate 30% of put electricity from renewables (and save about 5% of
fuel if that) we would need some way of handling a random 0-40GW
negative load on the grid. with our 8GW of nuclear, that would mean on
windy summer nights we would be throwing away up to 15GW of wind because
it cant be stored and we wouldn't need it. But on cold winter days with
no wind we might be short by 50GW and no amount of smart grid is going
to suddenly reduce demand from 55GW to 8GW or anything like it. That's
not even enough to run the trains.

SO it is easy to see that smart grids do feck all to actually cope with
renewable intermittentcy, in exactly the same way that renewable energy
does feck all to reduce carbon emissions.

They both represent solutions to the problem of appearing to Do
Something About Climate change whilst making a ****ing big profit and
not actually doing anything at all. All they have to do is convince an
unsophisticated electorate with no real idea about how anything works,
with a plausible narrative that conforms to their belief systems A
country full of harrys, in fact.

Its pure political fraud. But then, what isn't?

Of course in the end you have to keep the lights on, which is why twenty
dirty coal plants are being rush built in germany to paper over the
cracks in renewable energy.

So they can say 'we are generating 80% of our electricity with
renewables' and fail to mention that they haven't actually reduced
carbon emissions one iota. In fact, they have increased them.

But Greens are that ****ing stupid they will believe that they have,
which is all that matters.



Andy


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.