On Fri, 03 May 2013 09:46:04 +0100, Andy Champ wrote:

On 03/05/2013 00:17, The Natural Philosopher wrote:
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.

OK, I think I get it. It's being a small fixed amount ahead of the grid
phase that means you are pushing power in. If you shove less steam into
the turbine you'll lead by less, and be putting less current in even
though your RMS voltage is the same.

But no-one answered my question - what has overall control of the grid
frequency? Some guy with a meter and a phone, calling the CCGT stations?

There is a mark one eyeball in use although this is a last resort

Unless there is a failure of duplicated data comms links no one uses the phone
to dispatch generation in the UK. The vast majority is predetermined a number of
hours or days ahead by keyboard pressing.

In terms of what controls the frequency there is legislation, a number of UK
Grid Codes that all generators have to comply with, upfront commercial
agreements between the Grid System Operator (National Grid) and a number of UK
Generation operators, and prediction processes at Grid System Control to get the
load and demand matched at all times

In the case of commercial agreements a generator may opt to support frequency
between the standard limits of 49.5 to 50.5 Hz and get paid nothing by the Grid
System Operator, but if they offer to support system frequency from say 49Hz to
51Hz they get paid more during the time that response is required.

How this is achieved in practice is the setting the generator governors* to
achieve the desired dynamic frequency response. The target value is **always**
50Hz. The response either side of that programmable depending on the commercial
arrangements.

* now just a couple of near anonymous boxes in a rack each with a processor
driving an actuator on a steam valve or a fuelling valve.


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