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?

Andy