Frequency response in the UK

[m3ntosan]

Anyone familiar with the ancillary service in the UK?

It looks a bit different than the UCTE/ENTSO one (or maybe just the terms).

Old UCTE:

- Primary response/reserve
- Secondary response/reserve
- Fast tertiary reserve
- Slow tertiary reserve

There's a wikipedia article (find below), but it looks a bit messy to me. And no straight info on National grid site either.


May you grow up to be righteous, may you grow up to be true...

 

[ScottyUK]

Did you find Section CC6.3 in the Grid Code? I agree it is a horrible document to interpret. There is also some Guidance for Generators.


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[m3ntosan]

Yes, thanks. I know the Grid Code. There's something in CC.A.3.4 .. but not very tidy. I guess I should search in some Balancing Market codes for more info.

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[ScottyUK]

Not quite sure what you're asking... can you explain a bit more?


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If we learn from our mistakes I'm getting a great education!

 

[m3ntosan]

I am looking for more info regarding how frequency response works in the UK.

For instance,I was unable to find something about tertiary reserve. What happens when you used all secondary reserve/response capacity?

I've noticed something called STOR - Short term operating reserve (small diesels owned by water utilities, hospitals, police hq, etc.) and I've never heard of something similar in Continental Europe.

Also I've noticed something called High frequency response -is this like fast tertiary reserve - down, for instance when you're using none of the secondary reserve and you get a large consumer tripping, you will be getting a slight increase in frequency, so you have to decrease some generation - part of tertiary reserve agreement? Or it's something mandatory for every generator?

I am sure that I can find the answers in the Grid code, but like you said "it is a horrible document to interpret".

May you grow up to be righteous, may you grow up to be true...

 

[ScottyUK]

I'm not familiar with 'tertiary reserve' but I think it may be what we know as 'spinning spare', i.e. generation capacity available on the system but not actually producing power, e.g. a plant running at 80% of declared capacity. Secondary response is measured over a period of minutes - tens of minutes - and during that time the plants with additional capacity available can be despatched to pick up the shortfall. Secondary reserve buys time for part-loaded plants to pick up the additional load. Between the pumped hydro schemes at Dinowig, Ffestiniog and Cruachan, the mid-merit plants, and the few peaking plants which we have in the UK the system 'should' be able to withstand loss of a major generating station. I know our frequency response performance was analysed by the Grid each time a major frequency excursion occured. I think the most severe disturbance I saw was when the 4GW station at Drax tripped a few years back.

I haven't come across 'STOR' and couldn't find it in the Grid Code. My guess is that it would be inconsequential as most of those examples have generation designed for emergency use as islanded systems and don't typically operate in parallel with the system. I can imagine that some of the embedded generation like CHP and wind power might have some impact, but I've never heard of them being governed by an Ancillary Services agreement.

The high frequency response is a means of dealing with loss of a major load or interconnector which would lead to an over-frequency condition. It's part of the Ancillary Services agreement, and may be mandatory: some Ancillary Services are required as a condition of connection where the behaviour of the generator would otherwise have an adverse effect on system operation, while other Ancillary Services may be provided under commercial terms where they benefit the Grid, such as provision of black start capability. Some examples in BC2.A.2.1.

It is a very detailed document but I find it is difficult to find a clear answer: it is a maze of cross-references which frequently seem to reference themselves in a closed loop while telling you nothing. A technical document written by lawyers.

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If we learn from our mistakes I'm getting a great education!

 

[m3ntosan]

My understanding is that STOR diesels have to connect in minutes and maintain the supply for an hour or so. The idea is that you trip some steel works, cold stores (by agreement - something called Frequency service) to keep the frequency level and you reconnect them back only after the equal demand of steel works is matched by STOR small diesels supply.

OK, so the spinning reserve it's something like fast tertiary reserve - fast hydro and spinning reserve. And standing reserve maybe there's something like slow tertiary reserve, power plants that can go online faster than 7 hours. But in here I've seen standing reserve means only STOR.

Starts to make sense

May you grow up to be righteous, may you grow up to be true...

 

[rmw]

Scotty,

I'm confused by the terminology. Wouldn't "spinning reserve" be the considered the secondary reserve and "non spinning reserve" be tertiary reserve?

And, at least on some of our grids in the USA, spinning reserve units don't have to actually be spinning and connected to be classified as 'spinning' reserve. If it can get on line and get to full power in 10 min, it can be put on the books as spinning reserve. I state that from a general understanding, not an actual code quotation.

Therefore many CT peakers are sitting there stone cold drawing pay as spinning reserve due to their ability to get up and on in 10 or less.

rmw

 

[ScottyUK]

Hi rmw,

I'll let the authors of the Grid Code answer this one...

Secondary Response
The automatic increase in Active Power output of a Genset or, as the case may be, the decrease in Active Power Demand in response to a System Frequency fall. This increase in Active Power output or, as the case may be, the decrease in Active Power Demand must be in accordance with the provisions of the relevant Ancillary Services Agreement which will provide that it will be fully available by 30 seconds from the time of the start of the Frequency fall and be sustainable for at least a further 30 minutes. The interpretation of the Secondary Response to a -0.5 Hz frequency change is shown diagrammatically in Figure CC.A.3.2.

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If we learn from our mistakes I'm getting a great education!

 

[m3ntosan]

rmw,

Not every spinning reserve is qualified for secondary response. And not every generation owner wants to participate because secondary response is used very often by the system operator.

Secondary reserve is definetly a spinning reserve.
Fast tertiary reserve may be spinning reserve and hydro/GT.
Slow tertiary reserve - generation units that could start in less than 7 hours - coal fired.

May you grow up to be righteous, may you grow up to be true...

 

[m3ntosan]

Later edit: Secondary response is used very often by the AGC, not the system operator itself

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[rmw]

I have been doing some research and I can't substantiate what I stated above. My day job takes me into the world of peakers a lot these days and I have had the comment made to me more than a few times that the ability to get on and up to full load within 10 minutes meant the difference between having to actually run (be spinning and synchronized) or just be ready.

It may that these statements were made to me by operator level personnel who mixed terminology or who themselves didn't understand the actual difference between spinning reserve or supplementary reserve or non spinning reserve.

As a ME, my main task was to insure that there was no impedement to their getting there in 10 minutes, not worring about how they were billing or being paid for their existence.

But, having had peaker operators actually state to me that they wanted to stay under 800 operating hrs per year to keep them from having to install, operate and maintain CEMS equipment told me that they were getting their revenue somewhere other than running the units (multiple unit site-not a small investment of capitol.)

Everything I have been able to find on the net today tells me that to be classified 'spinning' the unit has to be synchronized among other requirements regarding time of response.

Notwithstanding that, it has been more than a few that have stated that their units were classified as 'spinning reserve' by virtue of their ability to get up and on in 10 minutes. And, some of these were utilities with huge consequential units in the 800 to 1300 MW range.

I am confused about what those comments might have meant now. I have heard it way too many times to have heard it wrong once or twice.

rmw

 

[m3ntosan]

Here's what RTE France thinks about secondary and tertiary reserve; maybe it helps you gain a better understanding.

• The aim of secondary control is to bring the frequency back to the reference frequency (50 Hz in general, 49.99 or 50.01 Hz in case of a "time adjustment") and the cross-border exchanges back to their scheduled values. This goal is met by modifying the set point capacity of the generation units subject to secondary power frequency control by means of a signal calculated on a centralised basis at the national dispatching centre.

• Tertiary control consists in activating balancing bids
to readjust the generation schedules on some sets in order to reconstitute the secondary reserve, or even part of the primary reserve when it is started, so as to provide protection against a new contingency. The corresponding actions are all under the control of control operators at the dispatching centres.

Tertiary reserve
The upward or downward tertiary reserve is the power that can be brought on line in less than half an hour. It is set up on the basis of balancing offers submitted on
the balancing mechanism which have a mobilisation time
compatible with the utilisation envisaged within the scope of the normal operation of this mechanism.

It consists of two parts:
• rapid tertiary reserve: power reserve that can be mobilised in less than 15 minutes, for a guaranteed period of at least one hour for each activation at least twice a day.
The purpose of the rapid tertiary reserve, which has a minimum value of 1,000 MW, is to supplement the contributions to secondary frequency control.Must make it possible to compensate for the outage of the largest connected generation set (which may be about 1,500 MW).
• additional tertiary reserve: power reserve which can be mobilised within a period between 15 minutes and half an hour, for a guaranteed period of at least six consecutive hours for each activation and at least once a day.
The additional tertiary reserve, which has a minimum value of 500 MW, is intended to reconstitute the rapid tertiary reserve.

Deferred reserve

Power which can be brought on line within a time of over half an hour and the use of which is ensured for a given consecutive duration. The deferred reserve makes it
possible, whenever necessary, to reconstitute the desired upward (or downward) level of tertiary reserve, therefore the operating margin level.



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