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