On Wednesday, April 20, 2022 at 2:44:26 AM UTC-7, palli...@gmail.com wrote:
> Martin Brown wrote:

> > They have always allowed the mains frequency to drift slightly with time
> > to accommodate minor imbalances in the load at peak times.
> ** Bullshit.

Maybe; the 'drift slightly with time' sounds vague.
> > Heavy load means lower frequency
> ** Bullshit.

Not so. Rotating machinery generates that frequency, and heavy load
on the generators does slow their rotation; regardless of control settings,
the feedback gain cannot be infinite (that causes more problems than it solves).

On 2022-04-20 19:59, whit3rd wrote:
> On Wednesday, April 20, 2022 at 2:44:26 AM UTC-7, palli...@gmail.com wrote:
>> Martin Brown wrote:
>
>>> They have always allowed the mains frequency to drift slightly with time
>>> to accommodate minor imbalances in the load at peak times.
>> ** Bullshit.
>
> Maybe; the 'drift slightly with time' sounds vague.
>
>>> Heavy load means lower frequency
>> ** Bullshit.
>
> Not so. Rotating machinery generates that frequency, and heavy load
> on the generators does slow their rotation; regardless of control settings,
> the feedback gain cannot be infinite (that causes more problems than it solves).
>

On the European mains network, the proportionality constant is
about 20GW/Hz. All sufficiently large generating facilities are
supposed to adjust their power output to drive the long-term
average frequency to its nominal value. A Swiss source provides
the reference frequency.

Jeroen Belleman

On Wednesday, April 20, 2022 at 4:49:38 AM UTC-4, Martin Brown wrote:
> On 18/04/2022 15:43, Ricky wrote:
> > On Monday, April 18, 2022 at 5:45:31 AM UTC-4, Martin Brown wrote:
>
> >> The calculation that wasn't allowed for in the UK is that with
> >> domestic generation on home roofs and on a sunny day when you shed
> >> "load" you will also shed a whole bunch of local solar PV
> >> generation as well.
> >
> > Let's leave the small, domestic systems out of the conversation.
> But they are critical to understanding one of the key modes of failure
> that took down so much of the UK grid. Roughly 2% of roofs have solar
> panels on each producing 4kW in good sunlight and at a time when average
> household load is about 200W so per thousand homes you have:
>
> 200kW load and 80kW local solar PV. The system tried to stabilise itself
> by shedding 1MW of load but at the same time it lost 400kW of local
> generation as well and so had to keep on dropping chunks off supply. It
> was always behind the curve at every step of the way. The algorithm
> expected to overshoot and then be able to reconnect. It didn't happen.
>
> As the number of homes with solar PV increases it becomes harder and
> harder to ignore this effect at >5% they become net exporters at least
> when the sun is shining.

I don't care about the issues in the UK. You and others have stated many times that the UK grid is bollixed up beyond all redemption. So not much to learn from it for a real grid.

> > The particular point someone was making was that no inverters used
> > with wind power (or solar farms) has the ability to help stabilize
> > the grid, because there is no rotating inertia. It was not claimed
> > that this was not possible, but it was implied by pointing out no one
> > had done this yet and it would be a very useful feature.
> There is some rotating inertia in the spinning wind turbine blades but
> nothing like as much as there is in a big mechanical steam turbine but
> enough to keep going provided that you allow the frequency to drift.
> > Seems to me it would require some way of increasing the power output,
> > which means the facility has to run below optimal efficiency to have
> > anything in reserve.
> One way to build some resilience is to have local battery storage that
> is immediately available to boost output when there is a sudden change
> in load. US & Australia has a fair sized one to control peak loading.
>
> https://www.bbc.com/future/article/20201217-renewable-power-the-worlds-largest-battery
>
> UK has one but it is a complete toy and wasn't in the right place to do
> any good last time. UK has a structural problem in that most power is
> generated in the north and shipped down to the south to be used. The
> upshot of this if they lose either of the big N-S EHT supergrid lines
> then the south is very short of electricity and something has to give.
>
> Pumped storage reservoirs are our most effective load balancing tool for
> immediate generation of more power. Routine balancing is done by
> adjusting power delivered the ultimate sink loads (on very favourable
> intermittent tariffs). Unfortunately if you have already asked them to
> power down you don't have that option (as has occurred some winters).

Yes, yes, yes, but not what we are discussing.

> > The advantage of natural inertia, is the continuous nature. As much
> > energy as is needed is available if you are able to tolerate the
> > reduction in frequency. Of course, there is a limit to the inertia
> > available, but it seems to do the job pretty well in most cases,
> > while currently we seem to get nothing from solar and wind power
> > facilities.
> You can still simulate inertia by allowing the inverter to drift further
> off frequency than the standard rules would normally allow. Something
> like this tweak has been done to avoid quite so much chaos next time.
>
> I presume that they have fixed the assumptions that caused the load
> shedding algorithms to misjudge how much *absolute* load they would
> have to drop to obtain a net saving of 1MW in future. It was a pretty
> catastrophic mode of cascade systems failure for what should have been a
> routine lightning strike with local cutout protection and recovery.
>
> I don't think it would be such a problem in the USA since peak solar PV
> output and peak domestic aircon requirements more or less balance it
> out. In the UK there is hardly any domestic aircon so that in sunny
> weather most of what is generated by domestic PV is exported to the grid
> (especially in the late afternoon).
>
> A stupid feature of the UK's "green" feed in tariff makes it cost
> effective to have solar PV power and turn it into domestic hot water!
> After market gizmos abound to do this automatically. You are deemed to
> export half of what you generate irrespective of using it or not.

Yes, you keep telling us how bad the UK grid is. I agree.

--

Rick C.

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On Wednesday, April 20, 2022 at 1:59:24 PM UTC-4, whit3rd wrote:
> On Wednesday, April 20, 2022 at 2:44:26 AM UTC-7, palli...@gmail.com wrote:
> > Martin Brown wrote:
>
> > > They have always allowed the mains frequency to drift slightly with time
> > > to accommodate minor imbalances in the load at peak times.
> > ** Bullshit.
> Maybe; the 'drift slightly with time' sounds vague.
> > > Heavy load means lower frequency
> > ** Bullshit.
> Not so. Rotating machinery generates that frequency, and heavy load
> on the generators does slow their rotation; regardless of control settings,
> the feedback gain cannot be infinite (that causes more problems than it solves).

No, that's not quite right. It is the balance between load and supply that causes the frequency drift. Too much energy feeding into the generators and the frequency increases as the excess is absorbed by the rotational inertia. Too little energy feeding into the generators and the frequency decreases as the inertia is drawn down to supply the excess load. The difference in source and load match determines the derivative of the frequency.

--

Rick C.

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On Wed, 20 Apr 2022 10:59:20 -0700 (PDT), whit3rd wrote:

> On Wednesday, April 20, 2022 at 2:44:26 AM UTC-7, palli...@gmail.com
> wrote:
>> Martin Brown wrote:
>
>> > They have always allowed the mains frequency to drift slightly with
>> > time to accommodate minor imbalances in the load at peak times.
>> ** Bullshit.
>
> Maybe; the 'drift slightly with time' sounds vague.
>
>> > Heavy load means lower frequency
>> ** Bullshit.
>
> Not so. Rotating machinery generates that frequency, and heavy load on
> the generators does slow their rotation; regardless of control settings,
> the feedback gain cannot be infinite (that causes more problems than it
> solves).

Right. In single generator operation the governor will be set to
constant frequency mode, and will hold a constant frequency at all
loads. But in order to parallel generators and share the load in a
stable manner the governors must be placed in droop mode, where a
percentage of power level is subtracted from the governors set point.
When paralleled with a much larger bus, the governor cannot regulate
generator speed, that is locked to the grid, it regulates real power
output instead. Connect initially with no load and slightly higher speed
at matched phase and the generator picks up a minute load, then if droop
is set at 5% for instance cranking up the governor speed knob 5% will
give you full load. So all rotating generators on the grid provide more
power as frequency drops and less as it rises, more power delivered tends
to up frequency, less reduces. Power delivery is set by the central grid
operator for all large generating stations in order to match the load and
thus keep frequency ~constant.

There is a similar situation with voltage regulation, in single generator
operation the field exciter regulates voltage. When paralleled with an
"infinite bus" the exciter can no longer regulate voltage, it
automatically (via aux contacts on the paralleling breaker) goes into
reactive power regulating mode, initially set at zero reactive power if
voltages were matched when paralleling and left there unless the utility
pays for reactive power. Multiple generators at the same location are
cross compensated to share reactive power, and reactive power on the grid
is balanced by the grid operator. There are some interesting stability
issues with reactive power since it has twice the effect on rotating
generator voltage as real power, but this is well understood if not easy
to remedy - as static synchronous generators increase in % total grid
power and need to contribute reactive power it will be necessary to turn
some control of them over to the grid operator, as is already being done
in some places, and as was done long ago to stop power sloshing between
rotating generator power plants on the same grid.

(Grid goes undervoltage, SSG's up reactive power, grid voltage goes up,
SSG's drop reactive power, grid goes undervoltage, etc. Better control
strategy will stop this.)

On Wednesday, April 20, 2022 at 6:21:31 PM UTC-4, Glen Walpert wrote:
> On Wed, 20 Apr 2022 10:59:20 -0700 (PDT), whit3rd wrote:
>
> > On Wednesday, April 20, 2022 at 2:44:26 AM UTC-7, palli...@gmail.com
> > wrote:
> >> Martin Brown wrote:
> >
> >> > They have always allowed the mains frequency to drift slightly with
> >> > time to accommodate minor imbalances in the load at peak times.
> >> ** Bullshit.
> >
> > Maybe; the 'drift slightly with time' sounds vague.
> >
> >> > Heavy load means lower frequency
> >> ** Bullshit.
> >
> > Not so. Rotating machinery generates that frequency, and heavy load on
> > the generators does slow their rotation; regardless of control settings,
> > the feedback gain cannot be infinite (that causes more problems than it
> > solves).
> Right. In single generator operation the governor will be set to
> constant frequency mode, and will hold a constant frequency at all
> loads. But in order to parallel generators and share the load in a
> stable manner the governors must be placed in droop mode, where a
> percentage of power level is subtracted from the governors set point.
> When paralleled with a much larger bus, the governor cannot regulate
> generator speed, that is locked to the grid, it regulates real power
> output instead. Connect initially with no load and slightly higher speed
> at matched phase and the generator picks up a minute load, then if droop
> is set at 5% for instance cranking up the governor speed knob 5% will
> give you full load. So all rotating generators on the grid provide more
> power as frequency drops and less as it rises, more power delivered tends
> to up frequency, less reduces. Power delivery is set by the central grid
> operator for all large generating stations in order to match the load and
> thus keep frequency ~constant.

The part I'm not clear on is how this is combined with the financial side of things. There are various load accounts and what you describe is generation essentially in bulk. No generator is outputing a specific amount as contracted for by customers. So how does the billing work? If user A, B and C have contracted with supplier K, but supplier K is having to output power according to central control, who is paying supplier K for all the MWh being pumped out if it doesn't match what his customers A, B and C are asking for?

--

Rick C.

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