Electricity Interconnectors

[LNW-GW Joint]

Looks like another five international interconnectors are going ahead, after Ofgem "greenlighting".
With nine links existing and two more under construction, that makes 16 to be in service by 2032.
These will have a combined capacity of 18 GW, but they are 2-way links so GB is never going to have access to all the capacity.
In fact today import and export is, perhaps unusually, closely balanced.

Details from the Ofgem site:

Empowering Great Britain for a clean and flexible energy future with the next generation of interconnectors

We have approved five major new undersea energy links to harness the potential of North Sea wind and help power millions of homes.

www.ofgem.gov.uk

In a major boost for energy security and the shift to clean power, Ofgem has today approved five major new undersea energy links which will further harness the vast potential of North Sea wind and help power millions of homes.
With Great Britain expected to be a net exporter of energy by 2030* the greenlit projects will capitalise on the growing amount of homegrown wind power by providing additional channels for exporting in times of energy surplus and importing during times of more limited domestic supply. Two of the projects will also create Great Britain’s first ever Offshore Hybrid Assets (OHAs) which can directly feed energy generated by offshore wind farms into both our own and European grids.

Summarising:

Existing links from GB:
France - 4GW via 3 links: IFA (Sellindge-Calais, 2GW), IFA2 (Solent-Caen, 1GW), Eleclink (Channel Tunnel, 1GW)
Belgium - 1GW via Nemo (Richborough-Zeebrugge)
Netherlands - 1GW via Nedlink/Britned (Isle of Grain-Maasvlakte)
Denmark - 1.4GW via Viking Link (Bicker Fen-Revsing)
Norway - 1.4GW via NSL (Blyth-Kvilldal)
Ireland - 1GW via 2 links: Moyle (Ayrshire-Antrim) and East-West (Rush-Shotton) links, each 0.5GW

Under construction:
Ireland - 0.5GW via Greenlink (Wexford-Pembroke), starts up 2025
Germany - 1.4GW via Neulink (Isle of Grain-Wilhelmshaven), just started construction, open 2029

New projects greenlit by Ofgem (target completion by 2032):
Germany - 1.4GW via the Tarchon link between Essex and Niederlangen, Germany
Ireland - 0.75GW via the Mares link between Bodelwyddan (North Wales) and Dublin
Ireland - 0.7GW via the LirlC link between Hunterston and Kilroot (NI)

And by interconnecting the GB grid to the off-shore nodes of the Dutch and Belgian networks:
Netherlands - 1.8GW via LionLink between Suffolk and the Dutch off-shore node
Belgium - 1.4GW via the Nautilus link between Isle of Grain and the Belgian off-shore node


Today's snapshot of electricity use is probably not typical (low wind, high gas usage). https://gridwatch.co.uk/
It shows at the moment 3.9GW being imported from France and Norway, with 1GW being exported to Ireland (quite usual), and 1GW each being exported to Netherlands and Denmark (which is quite unusual, maybe reflecting their lack of wind power under the current high pressure dome).
So that's only a net 0.9GW being imported to the GB network (the power companies make money whichever way the power flows).
IFA2 has only just restarted after an extended break, and the Channel Tunnel Eleclink has been out of use for a while.

There are also domestic GB interconnectors, notably the Hunterston-Deeside undersea cable (2.25GW).
Several other domestic interconnectors are planned between Scotland and England via the North Sea.

The cable and construction companies will be busy over the next few years.
They all seem to be foreign-owned, but no doubt there will be significant British content in project delivery..

 

[Bald Rick]

Good summary.

Yes it is unusual to be exporting at that level to the Netherlands and Danes, but this is a sign of things to come with all the wind we have coming on line. We’ve been exporting to Norway recently too.

One hopes that the new XLCC cable factory in Hunterston will pick up much of this work.


No mention of the XLinks project, but I guess that strictly speaking that isn’t an interconnector, just a 4000km, 3.6GW extension lead.

 

[brad465]

No mention of the XLinks project, but I guess that strictly speaking that isn’t an interconnector, just a 4000km, 3.6GW extension lead.

I often wonder why this project is going to the UK, considering there are 3 countries at least that would be closer and cheaper which the cables follow the coastlines of anyway. I'd have thought it would be more sensible to have a link from Morocco to Iberia, then another to the UK, where Spain/Portugal could consume the Moroccan power and the UK could take surplus power from these as a result of receiving the aforementioned supply.

 

[Bald Rick]

I often wonder why this project is going to the UK, considering there are 3 countries at least that would be closer and cheaper which the cables follow the coastlines of anyway. I'd have thought it would be more sensible to have a link from Morocco to Iberia, then another to the UK, where Spain/Portugal could consume the Moroccan power and the UK could take surplus power from these as a result of receiving the aforementioned supply.

They’ll have done the maths. I suspect the issue is the variabily on market prices around europe given different prevailing weather conditions; and the need to negotiate transit with 2-3 different system operators .

 

[m0ffy]

Most of the existing links and two of the new links are part-owned by National Grid Ventures - part of the UK’s National Grid PLC. They’re operated as joint ventures between NGV and the connected-state’s transmission network operator.

 

[HSTEd]

I often wonder why this project is going to the UK, considering there are 3 countries at least that would be closer and cheaper which the cables follow the coastlines of anyway. I'd have thought it would be more sensible to have a link from Morocco to Iberia, then another to the UK, where Spain/Portugal could consume the Moroccan power and the UK could take surplus power from these as a result of receiving the aforementioned supply.

Because this would mean that, in the case of a serious shortage of electricity, the intermediate operators would be capable of seizing the supply in Morocco for their own systems.

 

[Ashley Hill]

It seems the export and import of power has been happening for years. I know nothing of the subject but here’s a short “Look at Life” film from 1964 on YouTube called Passport to Power. It explores how power is transferred around various countries according to demand and surplus.

 

[Cloud Strife]

The cable and construction companies will be busy over the next few years.

A good example is in the Baltic States, where they will finally (next February) disconnect themselves from the IPS/UPS grid and join the Continental Europe grid instead, helped by the creation of quite a few interconnects in recent years.

I wonder if there are are plans in the future to synchronise the GB and Irish grids, given the plan to build more and more interconnects?

 

[m0ffy]

I wonder if there are are plans in the future to synchronise the GB and Irish grids, given the plan to build more and more interconnects?

I wouldn’t entirely rule it out, but I would be very, very surprised if this happened. All of the existing and planned interconnectors are DC links, which could not be readily converted to three-phase AC, and that’s before we get to the significant political undertaking involved in becoming one synchronous system.

 

[Merle Haggard]

I wouldn’t entirely rule it out, but I would be very, very surprised if this happened. All of the existing and planned interconnectors are DC links, which could not be readily converted to three-phase AC, and that’s before we get to the significant political undertaking involved in becoming one synchronous system.

Just out of idle interest, do you know the voltage?
Schoolboy physics lessons always suggested trunk electricity transmission was A.C. for sound theoretical reasons.

 

[edwin_m]

Just out of idle interest, do you know the voltage?
Schoolboy physics lessons always suggested trunk electricity transmission was A.C. for sound theoretical reasons.

That was and still is so transformers could be used to step the voltage up to the highest practicable, which minimises resistance losses and conductor sizes, then back down at the other end. For countries with land borders it has historically made technical sense to interconnect and synchronise their grids using the same overhead cables as used domestically. This maximises grid resilience, although there is a limit to how big an AC grid can be due to phase shifts over long transmission distances.

More recently power electronics has advanced enough to convert power to high voltage DC and back to AC again. I can think of three potential (pun intended) reasons to use DC for an interconnector:

• The AC networks either end don't have to be synchronous to each other - the inverter at the end of the link aligns itself to the local grid phase.
• DC has less loss to capacitance, particularly for an underground link where the conductors are close together.
• Underground cables have to be insulated, and the amount of insulation depends on the maximum voltage. The peak voltage of the AC cycle is about 1.4 times the RMS voltage that determines the amount of power transmitted. For DC the peak voltages is the same as the nominal voltage (with allowances for over-voltage in both cases). So DC can have less insulation for the same power, or more power for the same insulation.

Overhead cables aren't practicable for sea crossings other than very short ones, and going underground instead means more reason to use DC rather than AC. So marine interconnectors are almost certain to be DC and therefore it isn't really possible or necessary to sychronise grids which are separated by water.

 

[m0ffy]

That was and still is so transformers could be used to step the voltage up to the highest practicable, which minimises resistance losses and conductor sizes, then back down at the other end. For countries with land borders it has historically made technical sense to interconnect and synchronise their grids using the same overhead cables as used domestically. This maximises grid resilience, although there is a limit to how big an AC grid can be due to phase shifts over long transmission distances.

More recently power electronics has advanced enough to convert power to high voltage DC and back to AC again. I can think of three potential (pun intended) reasons to use DC for an interconnector:

• The AC networks either end don't have to be synchronous to each other - the inverter at the end of the link aligns itself to the local grid phase.
• DC has less loss to capacitance, particularly for an underground link where the conductors are close together.
• Underground cables have to be insulated, and the amount of insulation depends on the maximum voltage. The peak voltage of the AC cycle is about 1.4 times the RMS voltage that determines the amount of power transmitted. For DC the peak voltages is the same as the nominal voltage (with allowances for over-voltage in both cases). So DC can have less insulation for the same power, or more power for the same insulation.

Overhead cables aren't practicable for sea crossings other than very short ones, and going underground instead means more reason to use DC rather than AC. So marine interconnectors are almost certain to be DC and therefore it isn't really possible or necessary to sychronise grids which are separated by water.

That’s the long and the short of it. Back-to-back AC-DC-AC connections are quite commonly used to connect asynchronous systems on the same land mass (such as the various balancing systems in the US).

 

[Merle Haggard]

That was and still is so transformers could be used to step the voltage up to the highest practicable, which minimises resistance losses and conductor sizes, then back down at the other end. For countries with land borders it has historically made technical sense to interconnect and synchronise their grids using the same overhead cables as used domestically. This maximises grid resilience, although there is a limit to how big an AC grid can be due to phase shifts over long transmission distances.

More recently power electronics has advanced enough to convert power to high voltage DC and back to AC again. I can think of three potential (pun intended) reasons to use DC for an interconnector:

• The AC networks either end don't have to be synchronous to each other - the inverter at the end of the link aligns itself to the local grid phase.
• DC has less loss to capacitance, particularly for an underground link where the conductors are close together.
• Underground cables have to be insulated, and the amount of insulation depends on the maximum voltage. The peak voltage of the AC cycle is about 1.4 times the RMS voltage that determines the amount of power transmitted. For DC the peak voltages is the same as the nominal voltage (with allowances for over-voltage in both cases). So DC can have less insulation for the same power, or more power for the same insulation.

Overhead cables aren't practicable for sea crossings other than very short ones, and going underground instead means more reason to use DC rather than AC. So marine interconnectors are almost certain to be DC and therefore it isn't really possible or necessary to sychronise grids which are separated by water.

Thanks for the explanation. Back in my schooldays you could only convert the voltage of A.C. currents...
Synchronising with the network itself is obviously essential, but what determines that network's particular timing? Do networks rely on a rotating generator? To be clear, I'm thinking of the point in real time at which a particular stage in the cycle occurs, not the periodicity. There seemed to be the suggestion in the 'meltdown' of e.m.u.s' computer systems on the G.N. the other winter, that all the electronically-produced A.C. 'hangs' on a rotating generator to set frequency and by inference the timing.

As an aside, it occurs to me that the replacement of the present distribution network that is radiating from power stations with one, for instance, from off-shore wind power could also be D.C.. Either less intrusive overhead lines or underground would seem to be possible.

 

[BingMan]

That’s the long and the short of it. Back-to-back AC-DC-AC connections are quite commonly used to connect asynchronous systems on the same land mass (such as the various balancing systems in the US).

The problem with running, say, the GB and Irish grids with an AC interconnect is the difficulty in resynchronising them in order to reconnect after the interconnect has being down.

This can be a problem even with the GB grid if it ever gets split into two separate parts

 

[Ediswan]

Synchronising with the network itself is obviously essential, but what determines that network's particular timing? Do networks rely on a rotating generator? To be clear, I'm thinking of the point in real time at which a particular stage in the cycle occurs, not the periodicity. There seemed to be the suggestion in the 'meltdown' of e.m.u.s' computer systems on the G.N. the other winter, that all the electronically-produced A.C. 'hangs' on a rotating generator to set frequency and by inference the timing.

This is rarely discussed. I believe (no source) the traditional way, with heavy lumps of rotating metal, was that a slight over-supply increased the rotational speed and a slight under-supply reduced it. The exact phase angle of the grid at any given moment came from this, not controlled directly. I do not know how this is handled now there is a diversity of supply technology.

 

[edwin_m]

This is rarely discussed. I believe (no source) the traditional way, with heavy lumps of rotating metal, was that a slight over-supply increased the rotational speed and a slight under-supply reduced it. The exact phase angle of the grid at any given moment came from this, not controlled directly. I do not know how this is handled now there is a diversity of supply technology.

I think there was another thread on this recently. From what I recall, traditionally they had some sort of meter to show the phase difference to the grid, tweaked the generator manually until it was close enough, then closed the contactor. Modern electronics will detect the phase automatically, just as an AC train does with regenerative braking, but there is an increasing issue with less mechanical inertia from fewer big generators making it more difficult to maintain phase stability.

 

[BingMan]

I think there was another thread on this recently. From what I recall, traditionally they had some sort of meter to show the phase difference to the grid, tweaked the generator manually until it was close enough, then closed the contactor. Modern electronics will detect the phase automatically, just as an AC train does with regenerative braking, but there is an increasing issue with less mechanical inertia from fewer big generators making it more difficult to maintain phase stability.

I recall from my days with the CEGB in the seventies that we had a device called a synchroscope.
It was a dial with two hands. One rotated at a fraction of the frequency of the grid, the other at the same fraction of the frequency of the generator you were wanting to connect to the grid. You adjusted the frequency of the generator until it was almost but not quite the same as the grid, Then when the two hands coincided you hit the contactor.
Connecting an out of phase genny would destroy it and I think that there was electronic protection to prevent that

 

[m0ffy]

I recall from my days with the CEGB in the seventies that we had a device called a synchroscope.
It was a dial with two hands. One rotated at a fraction of the frequency of the grid, the other at the same fraction of the frequency of the generator you were wanting to connect to the grid. You adjusted the frequency of the generator until it was almost but not quite the same as the grid, Then when the two hands coincided you hit the contactor.
Connecting an out of phase genny would destroy it and I think that there was electronic protection to prevent that

I seem to recall the practice was (is?) for the generator to be slightly ahead of grid frequency. FWIW, one of my colleagues mis-synchronised a generator, ripping it from its concrete base.

 

[Merle Haggard]

This is rarely discussed. I believe (no source) the traditional way, with heavy lumps of rotating metal, was that a slight over-supply increased the rotational speed and a slight under-supply reduced it. The exact phase angle of the grid at any given moment came from this, not controlled directly. I do not know how this is handled now there is a diversity of supply technology.

That was how I understand it as well; heavy rotating masses with high inertia/momentum that the other sources rely on to provide the phase and timing.
My puzzle is what happens as these are closed down; in the 100% renewable electricity generating world, will there be any???

 

[m0ffy]

Yes. NESO (the National Energy System Operator, successor to National Grid ESO), is commissioning grid-stabilising flywheels for this purpose, according to this link:

Energy grid blackouts to be warded off with flywheel storage

Britain’s new National Energy System Operator (NESO) is reportedly drawing up a plan to fit a string of huge flywheels to the grid to store power and ward...

www.proactiveinvestors.co.uk

That was how I understand it as well; heavy rotating masses with high inertia/momentum that the other sources rely on to provide the phase and timing.
My puzzle is what happens as these are closed down; in the 100% renewable electricity generating world, will there be any???

 

[Merle Haggard]

Yes. NESO (the National Energy System Operator, successor to National Grid ESO), is commissioning grid-stabilising flywheels for this purpose, according to this link:

Energy grid blackouts to be warded off with flywheel storage

Britain’s new National Energy System Operator (NESO) is reportedly drawing up a plan to fit a string of huge flywheels to the grid to store power and ward...

www.proactiveinvestors.co.uk

Thank you, interesting.
Now I'm not shooting the messenger but the report seems (I may have misunderstood it) to conflate two mutually-exclusive objectives. If these flywheels are to provide the reference point of frequency and timing, they must always run at constant speed, but, if they are used to generate electricity (when other sources are down) using their momentum this will slow them down - the electrical energy comes from the conversion from kinetic energy.

 

[edwin_m]

Thank you, interesting.
Now I'm not shooting the messenger but the report seems (I may have misunderstood it) to conflate two mutually-exclusive objectives. If these flywheels are to provide the reference point of frequency and timing, they must always run at constant speed, but, if they are used to generate electricity (when other sources are down) using their momentum this will slow them down - the electrical energy comes from the conversion from kinetic energy.

I read it that they do the same as the traditional spinning generators. If either supply or demand changes suddenly they feed power to or from the grid to keep the frequency nearer 50Hz than would otherwise be the case, hopefully for long enough that the grid operator can address the problem by switching other suppliers on or off.

In principle I think the various inverters feeding the grid could be specified to increase power and advance their phase a tiny bit if the frequency is currently below 50Hz, and reduce and retard it a tiny bit if over. But there might be practical problems with this, such as setting off a frequency oscillation if everyone does that at the same time.

 

[Merle Haggard]

I read it that they do the same as the traditional spinning generators. If either supply or demand changes suddenly they feed power to or from the grid to keep the frequency nearer 50Hz than would otherwise be the case, hopefully for long enough that the grid operator can address the problem by switching other suppliers on or off.

In principle I think the various inverters feeding the grid could be specified to increase power and advance their phase a tiny bit if the frequency is currently below 50Hz, and reduce and retard it a tiny bit if over. But there might be practical problems with this, such as setting off a frequency oscillation if everyone does that at the same time.

Thank you for the reply, but... Perhaps I'm being slow (or difficult...); the traditional generators have an external source of power so can keep rotating at the right speed when demand changes. The flywheels, however, are powered by line current, so when this fails and they are used to generate electricity how will they maintain critical speed? I accept that, if no load is applied and line power is lost, they will only lose speed very slowly indeed. It's how they both retain speed and produce electrical energy that I can't grasp. But perhaps it's only for a few seconds, as you suggest, while alternatives are loaded, and even with a load the slowdown is within acceptable boundaries.

Designing a several hundred tonne flywheel to take the stresses of the sudden application of a load will be an interesting exercise for someone. There's a lot of kinetic energy in the rim, and lots of metal wanting to go in a straight line.

 

[edwin_m]

Thank you for the reply, but... Perhaps I'm being slow (or difficult...); the traditional generators have an external source of power so can keep rotating at the right speed when demand changes. The flywheels, however, are powered by line current, so when this fails and they are used to generate electricity how will they maintain critical speed? I accept that, if no load is applied and line power is lost, they will only lose speed very slowly indeed. It's how they both retain speed and produce electrical energy that I can't grasp. But perhaps it's only for a few seconds, as you suggest, while alternatives are loaded, and even with a load the slowdown is within acceptable boundaries.

Designing a several hundred tonne flywheel to take the stresses of the sudden application of a load will be an interesting exercise for someone. There's a lot of kinetic energy in the rim, and lots of metal wanting to go in a straight line.

They will change speed when generating (or absorbing) grid energy, and the grid frequency will therefore change. But by much less than if they weren't there.

 

[Merle Haggard]

They will change speed when generating (or absorbing) grid energy, and the grid frequency will therefore change. But by much less than if they weren't there.

Thanks, understand.

 

[BingMan]

I seem to recall the practice was (is?) for the generator to be slightly ahead of grid frequency. FWIW, one of my colleagues mis-synchronised a generator, ripping it from its concrete base.

At the old Agecroft power station there was a room with hunks of generator embedded in the wall ,ceiling and floor. A lesson to usto be very carefull of the synching.

 

[Ediswan]

At the old Agecroft power station there was a room with hunks of generator embedded in the wall ,ceiling and floor. A lesson to usto be very carefull of the synching.

At the risk of going off topic ... when that process goes wrong, does all the energy come from within the power station, or does some also get pulled in from the grid ?

 

[edwin_m]

At the risk of going off topic ... when that process goes wrong, does all the energy come from within the power station, or does some also get pulled in from the grid ?

I'd guess from the grid, considering the generator is designed to handle whatever power the turbine can send it.

 

[ninja-lewis]

Just out of idle interest, do you know the voltage?
Schoolboy physics lessons always suggested trunk electricity transmission was A.C. for sound theoretical reasons.

HVDC links are between 100 kV to 800 kV with the current UK links ranging from 200 kV to 600 kV.

The Chinese have a 1,100 kV UHVDC link stretching 2,046 miles to transfer 12 GW.

 

[mbonwick]

That was how I understand it as well; heavy rotating masses with high inertia/momentum that the other sources rely on to provide the phase and timing.
My puzzle is what happens as these are closed down; in the 100% renewable electricity generating world, will there be any???

Yes, one of the 4 units in Cruachan pumped hydro scheme is now contracted as inertia rather than generation. So rather than providing power, the turbine is powered to 600rpm.