3.5 South Wales and South England boundaries

The region includes the high demand area of London, generation around the Thames estuary and the long set of circuits that run around the south coast and South Wales. Interconnection to Central Europe is connected along the south east coast and this interconnection has significant influence on power flows in the region by being able to both import and export power with Europe.

The figure shows likely power flow directions in the years to come up to 2030. 

 

The arrows in the diagram are meant to give illustration to power flows and an approximate scale to the flow magnitude in winter peak when importing energy to the UK on the interconnectors

The South of England transmission region includes boundaries B13, B14, LE1, SC1, SC1.5, SC2, SC3 and SW1.

Regional Drivers

European interconnector developments along the south coast could potentially drive very high circuit flows causing circuit overloads, voltage management and stability issues.

The Leading the Way scenario suggests that 14GW of interconnectors and energy storage capacity may connect in the south. 

As interconnectors and storage are bi-directional, the south could see their capacity provide up to 14GW power injection or 14GW increased demand. This variation could place a very heavy burden on the transmission network. 

 

Most of the interconnectors will be connected south of boundary SC1 so the impact can be seen later in the chapter in the SC1, SC1.5 and SC2 requirements. 

If the south-east interconnectors are importing from the Continent and there is a double-circuit fault south of Kemsley, then the south–east circuits may overload and there could be significant voltage depression along the circuits to Lovedean. 

With future additional interconnector connections, the south region will potentially be unable to support all interconnectors importing or exporting simultaneously without network reinforcement. Overloading can be expected on many of the southern circuits. 

The connection of the new nuclear generating units at Hinkley may also require reinforcing the areas surrounding Hinkley. With new interconnector and generation connections, boundaries SC1, SC1.5, SC2, SC3, LE1 and B13 will need to be able to support large power flows in both directions which is different from today when power flow is predominantly in one direction. 

South Wales has seen some generation closures recently, freeing some transmission capacity, but the power export capacity out of the area remains tight. If there is growth in generation capacity in the area, the transmission capacity could be limiting.

In a highly decentralised scenario like Leading the Way, local generation capacity connected at the distribution level in this region could reach up to 14GW by 2040. Of that capacity, a typical embedded generation output on average might be around 5-10GW. 

This will vary depending on factors like wind speeds, and how other local generators decide to participate in the market and capacity available on the distribution networks.

The transmission network in the south is heavily meshed in and around the London boundary B14 and the Thames estuary, but below there and towards the west the network becomes more radial with relatively long distances between substations. 

The high demand and power flows may also lead to voltage depression in London and the south-east. The closure of conventional generation within the region will present added stability and voltage depression concerns which may need to be solved through reinforcements.

In the future, the southern network could potentially see a number of issues driven by future connections. If the interconnectors export power to Europe at the same time that high demand power is drawn both into and through London then the northern circuits feeding London will be thermally overloaded. 

The NOA 2020/21 will assess the likelihood and impact of the above mentioned potential scenarios and accordingly recommend preferred reinforcements for the South of England transmission region

Boundary Regions

Click on the regions below to expand the boundary and understand its capability and challenges.

If you would like to learn how to interpret the graphs, click the button below.

Find out more

The graphs show a distribution of power flow for each scenario, in addition to the boundary power transfer capability and NETS SQSS requirements for the next twenty years. 

Each scenario has different generation and demand so produces different boundary power flow expectations. 

From applying the methodology in the NETS SQSS for wider boundary planning requirements (as discussed in section 2), we determine: 

  • the economy criteria - solid coloured line
  • security criteria - dashed coloured line
  • current boundary capability – solid black line

The current boundary capability is expected boundary capability for the coming 2020/21 year’s winter peak study. This will change over time as the network, generation, and demand change, all of which are uncertain and so a straight back line shows the present capability.

The calculations of the annual boundary flow are based on unconstrained market operation, meaning network restrictions are not applied. This way, the minimum cost generation output profile can be found. 
We can see where the expected future growing needs could be by looking at the free market power flows in comparison with boundary capability.

Using the B6 boundary charts as an example below, there are four charts – one for each of the scenarios in the FES.

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On each graph, the two shaded areas provide confidence as to what the power flows would be across each boundary:

  • the darker region shows – 50% of the annual power flow or the 75th percentile in the range of power flows
  • the lighter region shows – 90% of the annual power flows or the 95th percentile in the range of power flows

From the regions, we can show how often the power flows expected in the region split by the boundary are within its capability (black line). 

If the capability of the boundary is lower than the two regions over the next 20 years, there might be a need for reinforcements to increase the capability. 

However, if the line is above the shaded regions, it shows that there should be sufficient capability here and that potentially no reinforcements are needed from a free market power flow perspective until the shaded regions exceed the capability (black line).

Close panel
Boundary B13 – South West

 

Wider boundary B13 is defined as the southernmost tip of the UK below the Severn Estuary, encompassing Hinkley Point in the south west and stretching as far east as Mannington. The southwest peninsula is a region with a high level of localised generation and demand.

Boundary flows and base capability

The boundary capability is currently a voltage compliance limit at 2.1GW for a double-circuit fault on Alverdiscott–Taunton circuits causing low voltage at Indian Queens substation.

It can be seen that until new generation or interconnectors connect there is very little variation in boundary requirements, and that the current importing boundary capability is sufficient to meet the short-term needs.

The large size of the potential new generators wishing to connect close to boundary B13 is likely to push it to large exports and require additional boundary capacity.

Boundary B14 – London

 

Boundary B14 encloses London and is characterised by high local demand and a small amount of generation. London’s energy import relies heavily on surrounding 400kV and 275kV circuits. 

The circuits entering from the north can be particularly heavily loaded at winter peak conditions.

The circuits are further overloaded when the European interconnectors export to mainland Europe as power is transported via London to feed the interconnectors along the south coast.

Boundary flows and base capability

The boundary capability is currently limited by thermal constraints at 11.6GW for a double-circuit fault on the Grain–Kingsnorth and Grain–Tilbury circuits.

As the transfer across this boundary is mostly dictated to the contained demand, the scenario requirements mostly follow the demand with little deviation due to generation changes.

The boundary requirements are close to each other across all four scenarios for security and economy required transfer. In both criteria, the required transfer is above 90% flows, meaning planning for these values covers all possible flows.

Boundary SC1 – South Coast

 

Boundary SC1 runs parallel with the south coast between the Severn and Thames estuaries.

At times of peak winter GB demand, the power flow is typically north to south across the boundary, with more demand enclosed in the south of the boundary than supporting generation.

Interconnector activity can significantly influence the boundary power flow. The current interconnectors to France, the Netherlands and Belgium connect at Sellindge, Grain and Richborough respectively

Boundary flows and base capability

The boundary capability is currently limited by voltage compliance at 4.1GW* for a double-circuit fault on the Kemsley–Clevehill and Kemsley–Canterbury circuits for interconnector import sensitivity. When the interconnector is exporting, voltage collapse occurs at 6.0GW of transfer. This happens after Bramley–Fleet double-circuit contingency.

*Positive values represent exporting power flows out of the south east area enclosed by the boundary, 

The interconnectors to Europe have a significant impact on the power transfers across SC1. A 2GW interconnector such as IFA can make 4GW of difference on the boundary from full export to full import mode or vice versa.

The biggest potential driver for SC1 will be the connection of new Continental interconnectors. With their ability to transfer power in both directions, boundary SC1 could be overloaded much more than normal with conventional generation and demand.

Across all four scenarios in the FES, the SQSS security required transfer follows a generally flat pattern, whereas the economy required transfer moves from exporting to importing in around 2023. The volatility of interconnector activity can be seen in the required transfers as the requirements swing from power flow south and north.

The SQSS calculation of required transfers does not place high loading on the interconnectors so the transfers are not seen to peak at very high values.

Boundary SC1.5 – South Coast

 

Boundary SC1.5 is a new boundary created between SC1 and SC2 to capture issues to the west of Nursling. The boundary crosses over the double circuits between Nursling – Mannington, Bramley – Fleet and Cleve Hill – Canterbury

At times of peak winter GB demand, the power flow is typically north to south across the boundary, with more demand enclosed in the south of the boundary than supporting generation.

Interconnector activity can significantly influence the boundary power flow. There is a new interconnector connecting at Chilling this boundary captures..

Boundary flows and base capability

The boundary capability is currently loading limited at 4.8GW*.

*Positive values represent exporting power flows out of the south east area enclosed by the boundary.

The interconnectors with Europe have a large impact on the power transfers across SC1.5 as a 2.0GW interconnector can make 4.0GW of difference on the boundary if it moves from import to export.

The volatility of interconnector activity can be seen in the wide spread of expected boundary flows depicted by the central darker band. Transfers (shown above) do not place high loading on the interconnectors so the transfers are not seen to peak at very high values.

Boundary SC2 – South Coast

 

SC2 is a subset of the SC1 boundary created to capture transmission issues specifically in the south part of the network between Kemsley and Lovedean.

The relatively long 400kV route between Kemsley and Lovedean feeds significant demand and connects both large generators and interconnection to Europe. A fault at either end of the route can cause it to become a long radial feeder which puts all loading on the remaining two circuits which can be restrictive due to circuit ratings and cause voltage issues.

Additional generation and interconnectors are contracted for connection below SC2 which can place additional burden on the region.

Boundary flows and base capability

The boundary capability is currently voltage stability limited at 4.8GW*

*Positive values represent exporting power flows out of the south east area enclosed by the boundary. 

The interconnectors with Europe have a large impact on the power transfers across SC2 as a 2.0GW interconnector can make 4.0GW of difference on the boundary if it moves from import to export.

The volatility of interconnector activity can be seen in the wide spread of expected boundary flows depicted by the central darker band  similar to SC1.5. 

Transfers do not place high loading on the interconnectors so the transfers are not seen to peak at very high values here either.

Boundary SC3 – South Coast

 

Boundary SC3 is created to capture transmission issues specifically in the south-east part of the network.

The current and future interconnectors to Europe have a significant impact on the power transfers across SC3. The current interconnectors to France, the Netherlands and Belgium connect at Sellindge, Grain and Richborough respectively.

Boundary flows and base capability

The boundary capability is currently limited by thermal loading about 6.2 GW for a double-circuit fault on the Grain–Tilbury–Kingsnorth circuits.

The current and future interconnectors to Europe have a significant impact on the power transfers across SC3 with their ability to transfer power in both directions.

Across all four scenarios in the FES, the SQSS security required transfer follows similar patterns and is mainly lower compared to the economy required transfer. In general, the economy required transfer faces a decline over the time, albeit it does not reflect the interconnectors uncertainties. The uncertainty of interconnector activity can be seen in the wide spread of the boundary flows depicted by the central darker band.

Boundary LE1 – South East

 

 

Boundary LE1 encompasses the south east of the UK, incorporating London and the areas to the south and east of it.

LE1 is characterised by two distinct areas. Within London, there is high local demand and little generation. The remainder of the area contains both high demand and high levels of generation.

In particular, there are a number of gas power generators in the Thames estuary area and an interconnector to the Netherlands, while connected to the south east coast are a number of wind farms, interconnectors to France and Belgium, as well as nuclear and gas power stations.

LE1 almost exclusively imports power from the north and west into the south east, and the purpose of the boundary is to monitor flows in this direction. With the existing and proposed interconnectors importing power from the Continent, power flows enter London from all directions, to the extent that flows across LE1 reduce and limited constraints are seen similar to those by B14 on the south coast boundaries.

However, with increased number of interconnectors, and (in some scenarios) increased likelihood of them exporting power in future years, LE1 can become a high demand area, with any locally generated power feeding straight into the interconnectors.

As such, the circuits entering LE1 from the north can become overloaded as power is drawn into and through London toward the south and east.

Boundary flows and base capability

The boundary capability is currently limited by thermal constraints at 7.6GW with overloads of the Rayleigh Main–Tilbury circuit.

Across all four scenarios in the FES, the SQSS economy required transfer grows beyond existing boundary capability from 2023 and the expected power flows are less than the required transfer and the uncertainty of interconnector activity can be seen in the wide range of the boundary flows

Boundary SW1 - South Wales

Boundary SW1 encloses South Wales is considered a wider boundary. Contained within the boundary is a mixture of generation types including gas combined cycle, coal, wind and solar. Some of the older power stations are expected to close but new generation capacity is expected to connect, including new generators powered by wind, gas, solar and tidal.

South Wales includes demand consumptions from the major cities, including Swansea and Cardiff, and the surrounding industry.

Boundary flows and base capability

The capability of SW1 is 2.9GW which is restricted by a thermal limits caused by the Imperial Park – Melksham circuits.

The SQSS boundary requirements are higher than the boundaries present boundary capability but the majority of the expected power flows stay within the capability. Therefore some constraints can be expected and some additional boundary capability may be beneficial.