Re: The Spanish Grid Drop-out - recently released information.

On 15/05/2025 5:14 am, Carlos E.R. wrote:

On 2025-05-14 16:16, Glen Walpert wrote:

On Tue, 13 May 2025 07:50:36 -0700, Don Y wrote:
>

On 5/13/2025 6:26 AM, Glen Walpert wrote:

I don't think that using broadcast radio for real time mains grid
control is a good idea. It would be far too unreliable.

>
Point to point RF links have been in use in (mostly hard wired) grid
control SCADA (System Control And Data Acquisition) systems for at
least 30 years, which is when a former employer did some work on a
SCADA upgrade project for the Egyptian Electrical Authority.  A search
on 'SCADA radio link' will turn up several vendors.

>
And they used these to control instantaneous frequency and phase?  Or,
just coarse data collection and /supervisory/ control?

>
SCADA is used to monitor and control the grid, where control is done in
real time by adjusting the set points for real and reactive power at all
controlled power sources.  A small percentage of sources being
inaccessible degrades control by an insignificant amount.
>
Real power is regulated by the prime mover governors, which must be
operated in droop mode in order to share the load (the speed set point is
reduced with increasing load).  The grid Hz/Gw figure which has been
mentioned is not directly related to generator inertia, where
insignificant energy is stored, it is the aggregate droop setting of the
prime mover governors feeding the grid.  After speed/frequency shift (the
governors only measure shaft speed) due to a load change the grid control
center adjusts the governor set points to bring the frequency back to
normal.
>
Voltage regulation is entirely separate and is done by setting the
reactive power output of sources, again by adjusting set points in real
time over SCADA (or one of the other approved standard comm protocols).
This is a bit complex for a quick explanation but is described in detail
in any decent text covering synchronous generator control.
>
Voltage regulation is more likely to be a stability issue than frequency.
If you take two widely separated generators or sets of locally paralleled
generators at two power plants which are optimally tuned for stand alone
operation and connect them with a long transmission line, voltage will
begin to oscillate due to the time delay in locally detecting changes in
the other plants output.  Detuning the regulators to achieve stability
results in inadequate response to load changes - thus central control of
both plants over SCADA.
>
Large generator voltage response time is limited by the L/R time constant,
which will be in the 10's of seconds, over a minute for some large multi-
pole hydroelectric generators.  Inverters can respond much faster, with
potentially worse stability issues, and dividing power sources into many
small units does not make stability any easier, you still can't set
optimal tuning parameters for widely separated groups of sources which
will be both stable and fast, central control of some percentage of source
set points is required.  This problem and it's solution is well understood
and the current generation of inverters are designed to allow remote
control of set points.
>
In the US more than 2/3 of all solar power is utility owned 10 MW or
larger and all of this is under central grid operator control, so no
stability issues there.
>
More intermittent power sources need more batteries, which are being
deployed by utilities as fast as they can be manufactured, being far
cheaper then peaking gas turbines, the most expensive of power sources.
>
<https://www.tdworld.com/distributed-energy-resources/energy-storage/news/
55287560/us-energy-storage-industry-commits-100-billion-investment-in-
american-made-grid-batteries>

 Wouldn't it be easier to have the entire distribution network using DC?
 just saying with a glass of wine in my hand :-)

That's probably correct, but it wouldn't be cheaper. It's probably true that taking DC down to the sub-station level could be cheaper, with today's technology, if you were starting from scratch, but since that kit is already there you would be throwing away a lot of big expensive transformers from the next level up, and replacing them with a lot of big, expensive - if less expensive - inverters. It would take a lot of capital investment to make the switch, and the people who operate the grid are adminstrators rather than entrepreneurs.
--
Bill Sloman, Sydney