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Posted by Eeyore on April 6, 2009, 2:05 pm
 


Tim Jackson wrote:


Well said Tim, and the EU has a population of > 500 million now. It makes the
USA look like a sideshow.

Graham


Posted by Scott on April 7, 2009, 1:28 am
 
On Mon, 06 Apr 2009 15:05:00 +0100, in alt.energy.homepower, Eeyore


Sorry, China's kicking your ass there.  If 3/5ths makes the US a sideshow,
5/13ths makes the EU look like an also-ran.  Of course we don't buy into the
idea that a greater population makes a superior...anything, now do we?


Posted by Eeyore on April 7, 2009, 2:05 am
 

Scott wrote:


Its electricity usage is rather lower.

Graham


Posted by Tim Jackson on April 6, 2009, 9:27 am
 Neon John wrote:

It may well be that the actual variance is smaller nowadays than when I
was interested in measuring it ??? years ago (it *was* at a particularly
demanding time for the industry), and it may be smaller in the US than
Europe, I wouldn't know.  That is not the point.

The point is that the grid frequency is a process variable of the grid
control systems, and is used to control the power input, it does vary,
and that variance, whether 0.5Hz, 0.1Hz or even 0.01Hz reflects
unanticipated load changes.  The amount of variation depends on the
feedback gain in the control loop, and the stability of the system
depends inversely on the gain. The faster your generators can respond,
the higher gain you can use and the less deviation you get.  The more
mass your generators are spinning the slower the reaction to load, and
the smaller the deviation.

So it makes some sense for non-critical appliances to briefly shut down
if the frequency dips (in terms whatever range of frequencies the grid
is operating), it sheds load far faster than the generator can raise
torque.  Exactly what effect that has on the efficiencies of e system as
a whole, however may be arguable.

Posted by Eeyore on April 7, 2009, 4:30 am
 

Tim Jackson wrote:


" The normal system frequency is 50Hz. As electricity cannot be stored, the
instantaneous generation must match the demand being taken from the system. If
the instantaneous demand is higher than the generation, the system frequency
will fall. Conversely, if the instantaneous generation is higher than the
demand, the frequency will rise. System frequency will therefore vary around
the 50 Hz target and National Grid has statutory obligations to maintain the
frequency within +/- 0.5Hz around this level. However, National Grid normally
operates within more stringent 'operational limits' which are set at +/- 0.2Hz.
"
http://www.nationalgrid.com/uk/Electricity/Data/Realtime/

Real Time Frequency Data - Last 60 Minutes
http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Frequency/Freq60.htm

Graham



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