National Grid Frequency

[aleggatta]

Most often at the higher end due to the DNOs not normally altering the previously set tapping 240volt of thier local distribution transformers

Mostly due to the transformers not featuring a 230v tapping point, so would result in lots of new transformers being required to replace kit that is not life expired. AFAIK new transformers are all 230/400v windings now as opposed to 240/415, however some locations might still warrent a 240v domestic supply if there are known volt drop issues in the area.

 

[Bletchleyite]

Many years ago I was in the National Grid Control centre, and I saw the data and graphs.

You can see them from the comfort of your computer screen, too:

https://www.gridwatch.templar.co.uk/

Fascinating stuff.

 

[GusB]

You can see them from the comfort of your computer screen, too:

https://www.gridwatch.templar.co.uk/

Fascinating stuff.

Fascinating, and also quite baffling. I've just spent a couple of hours googling, and I'm still none the wiser as far as the technical side of it is concerned. We covered some of the basics in my last year at school, but by the time I got to university I realised that electricity generation was probably a bit beyond me. A field trip to Peterhead power station on a dull, wet November day was probably the moment when I realised I'd picked the wrong course!

 

[Bald Rick]

You can see them from the comfort of your computer screen, too:

https://www.gridwatch.templar.co.uk/

Fascinating stuff.

Yes, and the Drax insights website allows you to more easily see historical data https://electricinsights.co.uk/#/homepage?&_k=92knjh

But being in the control centre itself you get to see it in a LOT more detail.

One thing from the graphs for the last 24 hours: because more wind is coming on line now it was covering nearly half the grid last night. Add in Nuclear, biomass and a few imports and we were very nearly carbon free last night. (AIUI The grid needs to keep some gas stations on line for supply security).

 

[Meerkat]

You are quite correct all domestic generation must disconnect from the mains in the event of mains power-loss to provide protection to the DNO staff carrying out any work on the disconnected mains

Do you mean disconnect the solar from the house mains, or disconnect the house mains from the street (latter meaning house still has power). I guess it’s cheaper to plug solar into nearest bit of house wiring so probably the former?

 

[hwl]

I guess it would be possible in principle for producers of power that feed the grid via inverters to modify their voltage and frequency to simulate the behavior of a rotating generator as discussed above, very much as a VVVF inverter on a traction package does but with a much smaller degree of variability. However I guess nobody thought to specify this so the inverters weren't designed with that capability.

The real challenge is much more complex than outlined above. The inverters can theoretically do that but there needs to be communication and active control. (they have to match grid frequency and timing but do this in a following manner not an active control type manner.)

The other thing not mentioned so far is that when the frequency drops the efficiency of the transmission and distribution networks also drops requiring more power to be generated and inductive loads (motors) also take more current as the frequency drops requiring more power to be generated too... I.e. whene the frequency starts to drop there are unhelpful feed back loop.

 

[InTheEastMids]

Do you mean disconnect the solar from the house mains, or disconnect the house mains from the street (latter meaning house still has power). I guess it’s cheaper to plug solar into nearest bit of house wiring so probably the former?

A rooftop solar array should (via an inverter) be connected by a dedicated cable to the consumer unit with its own fuse/switch.

We're not talking about a physical disconnection here. If I remember correctly, the G83 standard requires that the inverter shuts down if the frequency falls below a threshold. These inverters do not have grid forming electronics and only operate in grid tied mode

 

[HSTEd]

Do you mean disconnect the solar from the house mains, or disconnect the house mains from the street (latter meaning house still has power). I guess it’s cheaper to plug solar into nearest bit of house wiring so probably the former?

The solar system is not allowed to generate into a dead line.
If there is no mains voltage present on the mains it switches off.

This is because the 230V could back feed and cause shocks to people elsewhere in the system working on what they think is an isolated supply.
This is especially true as it can even produce 11kV on the high voltage network by back-feeding through transformers.

 

[DelW]

The pumped-storage scheme that needed the Ffestiniog Railway diverting is TanyGrisiau. Dinorwic is its subsequent, bigger brother, and is at Llanberis. As I understand it, Tanygrisiau was primarily built to smooth-out demand between peak and off-peak loads, using cheap electricity to pump the water up, and then letting the water back down to generate expensive electricity at peak times. However, once it was built, its ability to cope with short-term demand was realised and became more important.

There is also Cruachan pumped storage scheme in the west of Scotland:
https://en.wikipedia.org/wiki/Cruachan_Power_Station

Cruachan Power Station (also known as the Cruachan Dam) is a pumped-storage hydroelectric power station in Argyll and Bute, Scotland. The scheme can provide 440MW of power and has a capacity of 7.1 GWh.

The turbine hall is located inside Ben Cruachan, and the scheme takes water between Cruachan Reservoir to Loch Awe, a height difference of 396 metres (1,299 ft). It is one of only four pumped storage power stations in the UK, and is capable of providing a black start capability to the National Grid.

Construction began in 1959 to coincide with the Hunterston A nuclear power station in Ayrshire. Cruachan uses cheap off-peak electricity generated at night to pump water to the higher reservoir, which can then be released during the day to provide power as necessary. The power station is open to visitors, and around 50,000 tourists visit it each year.

The fourth one mentioned is at Foyers, also in Scotland.

 

[hwl]

Do you mean disconnect the solar from the house mains, or disconnect the house mains from the street (latter meaning house still has power). I guess it’s cheaper to plug solar into nearest bit of house wiring so probably the former?

Both are possible and done but the former is far cheaper than the later hence no surprises what the most common installation type is!

0 - 1.8GW in 16 seconds. Not instant, but prett dam(ned) close!

That is in quick start mode which needs the turbines to spinning (dry) at grid speed (done using grid electricity) before the valves are opened.

Well that depends on the size of the power station....however (back of fag packet estimates follow...)

Currently GB rail takes a little less than 2% of the GB grid supply for traction electricity, or an average of (about) a constant 500MW over the course of a year. In reality this will be about a tenth of that between midnight and 0500, but up to around 800MW at peak times.

Whilst only 36% (2018 figure, it may well be 38% now) of the network is electrified, most of the electric network deals with fast and/or frequent and/or long trains, which are more power hungry than most of the non-electrified network were it to be electrified.

It is therefore reasonable to assume that approximately 75% of all current vehicle miles are electrically propelled. (I’m sure there’s a stat confirming this out there somewhere, but I can’t find it).

68% of passenger vehicle miles were electric at the end of CP4 before the current round of electrification came on line. An updated stat is due shortly...With GW and Scottish electrification schemes and the increased size of Thameslink fleet it will be around 75%.

Therefore if the entire rest of the network was electrified, it would represent an extra 33% power required assuming a like for like service frequency / length / speed. Being bold, let’s assume that electrification delivers longer / faster / more frequent trains, so we actually need an extra 50%. That’s equivalent to an average demand of 250MW over a year, peaking at around 400MW.

In context, the government recently agreed deals for three new wind farms, each with a capacity of around 1,200MW. Hinckley Point and the proposed Sizewell C are each 3,200MW. Drax is almost 4,000MW.

Therefore the answer is “as little as 1/10th of a power station”

Some useful data from the ORR here; it’s a year and a half old, and the amount o power used for electric trains will have risen notably in that time due to the roll out of the new GW fleet and further electrification in the Midlands, NW and Scotland.
https://dataportal.orr.gov.uk/media/1114/rail-infrastructure-assets-environmental-2017-18.pdf

 

[Meerkat]

The solar system is not allowed to generate into a dead line.
If there is no mains voltage present on the mains it switches off.

This is because the 230V could back feed and cause shocks to people elsewhere in the system working on what they think is an isolated supply.
This is especially true as it can even produce 11kV on the high voltage network by back-feeding through transformers.

Thanks. Wonder how many folk are disappointed when having their own generation doesn’t keep the lights on!

 

[RLBH]

Thanks. Wonder how many folk are disappointed when having their own generation doesn’t keep the lights on!

It is rather an obvious thing to expect when you have your own generation! As noted, it can be done that way, but needs a more complex, and therefore more expensive, installation.

I gather that in the US, where power outages due to extreme weather are fairly common, and respect for 'the man' is limited, there are quite a few DIY generator installations - both renewable and diesel - that overlook such regulatory niceties. This makes the life of recovery crews after the said extreme weather even more interesting than it already was.

 

[DaleCooper]

The frequency of the power you get at home should always be within 1% of 50Hz, but the voltage could be 10% over or 6% under 230V.

If I remember correctly the average frequency over a 24 hour period is required to be held to a much closer tolerance than the short term variation of 1%.

 

[OneOffDave]

It is rather an obvious thing to expect when you have your own generation! As noted, it can be done that way, but needs a more complex, and therefore more expensive, installation.

I gather that in the US, where power outages due to extreme weather are fairly common, and respect for 'the man' is limited, there are quite a few DIY generator installations - both renewable and diesel - that overlook such regulatory niceties. This makes the life of recovery crews after the said extreme weather even more interesting than it already was.

I've worked in a number of environments where we needed uninterruptable power and one of the most expensive bits of the system was the auto switchgear to disconnect us from the mains when the mains supply failed and ensure that the on site generation didn't kick in until that had happened. Battery based UPS on key equipment covered that switch over phase. A bit of a sledgehammer to crack a nut at the domestic level

 

[hwl]

I've worked in a number of environments where we needed uninterruptable power and one of the most expensive bits of the system was the auto switchgear to disconnect us from the mains when the mains supply failed and ensure that the on site generation didn't kick in until that had happened. Battery based UPS on key equipment covered that switch over phase. A bit of a sledgehammer to crack a nut at the domestic level

Exactly but something that should be able to be addressed to an extent if there is seen as being a sufficient market for it.

 

[axlecounter]

The alternators will produce an output with a frequency that is tied directly to their rotating speed.
If you remove more energy from the alternators than is provided to them by whatever they are coupled to, they will slow down and thus the output frequency will drop.

This is traditionally the method used to control grids, the governors on steam turbines would be set to monitor grid frequency and increase turbine power if the frequency falls, or reduce power if it rises.
This allows the grid to be controlled without any communication between generating plants.

With my very limited understanding, this raises the question: why would the frequency drop when (if) power is generated (only) by non-rotating or better asynchronous generators? Shouldn’t in that case the voltage alone drop?

Very interesting topic.

 

[hwl]

With my very limited understanding, this raises the question: why would the frequency drop when (if) power is generated (only) by non-rotating or better asynchronous generators? Shouldn’t in that case the voltage alone drop?

Very interesting topic.

No, it is a lot more complicated than that.

for example see the second half of one of my previous comments
https://www.railforums.co.uk/threads/national-grid-frequency.193206/page-2#post-4236474

...
The other thing not mentioned so far is that when the frequency drops the efficiency of the transmission and distribution networks also drops requiring more power to be generated and inductive loads (motors) also take more current as the frequency drops requiring more power to be generated too... I.e. whene the frequency starts to drop there are unhelpful feed back loop.

With AC the energy delivered can be though of as the area between the sine curve and 0, which is defined by 3 components the voltage, current (the PF is unlikely to be 1 so the common area of the voltage and current curves) and frequency which are not independent of each other.
If the voltage start to drop so will the frequency which has further nasty feedback issues. With inductive loads as the frequency drops the PF also drops.

The NG report is very clear there is no real substitute for rotational inertial to keep the frequency stable.

The equipment at the windfarm connection substation protection equipment tried to follow the modified lightening strike + grid voltage curve profile in a lagging way which got out of control and eventually shut down when trying to fight (with several hundred MW) the grid on single "struck" phase and ending up very out of phase before shutting down.

 

[Goofle]

There is an interesting near-realtime chart showing how and when it is used at
https://www.gridwatch.templar.co.uk/
Regards, Paul.

Am I reading this right in saying that only about 1.5% of demand is supplied by coal fired power stations??

 

[GRALISTAIR]

I just wanted to say @a_c_skinner thanks for starting an absolutely fascinating and informative thread that of course is related to railway electrification etc.

 

[Mordac]

At the moment. If you want more background data over more extended periods of time, the Department for Business regularly publishes a bulletin called Energy Trends: https://www.gov.uk/government/collections/energy-trends

 

[Kingspanner]

Am I reading this right in saying that only about 1.5% of demand is supplied by coal fired power stations??

Yes you are. Since the government announced that they would not allow unabated (i.e. without carbon capture and storage) coal generation after 2025, coal plants have gone off-line and stayed off as soon as major overhauls or other repairs become necessary. The latest coal fired station to go is Cottam https://www.bbc.co.uk/news/av/uk-en...fired-power-station-turned-off-for-final-time
Coal cannot compete on price against nuclear or wind, and cannot compete on emissions against gas. The only room is when demand is very high and all other generation is flat out.

 

[Goofle]

Yes you are. Since the government announced that they would not allow unabated (i.e. without carbon capture and storage) coal generation after 2025, coal plants have gone off-line and stayed off as soon as major overhauls or other repairs become necessary. The latest coal fired station to go is Cottam https://www.bbc.co.uk/news/av/uk-en...fired-power-station-turned-off-for-final-time
Coal cannot compete on price against nuclear or wind, and cannot compete on emissions against gas. The only room is when demand is very high and all other generation is flat out.

Thank you - an interesting (and surprising!!) web page!

 

[HSTEd]

With my very limited understanding, this raises the question: why would the frequency drop when (if) power is generated (only) by non-rotating or better asynchronous generators? Shouldn’t in that case the voltage alone drop?

Very interesting topic.

For one thing, because they have been built to ensure that voltage remains largely constant and use frequency to signal a need for generation.

However, the frequency in non-rotating systems will still be somewhat supported by large synchronous (and to a lesser extent induction) motors connected as loads.

But non-rotating systems are notoriously unstable in this regard.

 

[a_c_skinner]

Well thanks to GRALISTAIR for the approval! As we are tolerating a pretty broad definition of what is on topic can I ask another:

How do they keep all the sources of power in phase?

Like other contributors I'm glad this wasn't how I was destined to earn my living. I never got beyond "that's clever" when looking at diagrams of three phase transformers.

 

[HSTEd]

How do they keep all the sources of power in phase?

Synchronous motors/generators want to stay in sync with the power supply phase. If they do not enormous currents will flow in the armature that will try to force the armature back into phase.

So once you carefully sync up the generator to the grid, and close the circuit breakers then they should tend to stay locked together unless something drastic happens.

 

[pj334]

Am I reading this right in saying that only about 1.5% of demand is supplied by coal fired power stations??

As Kingspanner said, coal power is in deep decline and will soon be no more. The bad news is that it is being replaced by gas fired combined cycle turbine generators (CCGT), which of course is a fossil fuel. These are typically being used to provide up to 50% of the total electrical demand. They each emit huge volumes of CO2, but because we don't see it (unlike smoke from a coal fired station), it is not so obvious. I was once informed that one set produces 200 tons of CO2 per hour; CO2 gas is not heavy so that must equate to a very large volume.

 

[hwl]

How do they keep all the sources of power in phase?

Mostly by getting them to match what is already running (as HSTEd posted the detail while I was typing), which works as long as you don't have black start and have a decent amount of inertia.

 

[hwl]

As Kingspanner said, coal power is in deep decline and will soon be no more. The bad news is that it is being replaced by gas fired combined cycle turbine generators (CCGT), which of course is a fossil fuel. These are typically being used to provide up to 50% of the total electrical demand. They each emit huge volumes of CO2, but because we don't see it (unlike smoke from a coal fired station), it is not so obvious. I was once informed that one set produces 200 tons of CO2 per hour; CO2 gas is not heavy so that must equate to a very large volume.

CCGT and wind are both running at about 30% of total so far today so quite a bit of coal is being replaced by wind.

 

[GRALISTAIR]

--- CO2 gas is not heavy so that must equate to a very large volume.

Well depends how you define it.
Air = 1.27 g/l
Nitrogen = 1.2506 g/l
Oxygen = 1.429 g/l
Argon = 1.784 g/l
CO2 = 1.98 g/l

So in terms of air quite a dense component.

As Kingspanner said, coal power is in deep decline and will soon be no more. The bad news is that it is being replaced by gas fired combined cycle turbine generators (CCGT), which of course is a fossil fuel.

True but it (natural gas) is cleaner - Coal is not pure carbon but it has high carbon content. When it burns it produces CO2. When gas burns (mainly methane) which is CH4, so when 1 molecule burns it produces 1 molecule of CO2 and 2 molecules of water.

 

[hwl]

Well depends how you define it.
Air = 1.27 g/l
Nitrogen = 1.2506 g/l
Oxygen = 1.429 g/l
Argon = 1.784 g/l
CO2 = 1.98 g/l

So in terms of air quite a dense component.



True but it (natural gas) is cleaner - Coal is not pure carbon but it has high carbon content. When it burns it produces CO2. When gas burns (mainly methane) which is CH4, so when 1 molecule burns it produces 1 molecule of CO2 and 2 molecules of water.

With energy from the water as steam partially recoverable in CCGTs...