Control Of The National Grid (Great Britain)

The National Grid is the high-voltage electric power transmission network supporting the UK's electricity market, connecting power stations and major substations, and ensuring that electricity generated anywhere on the grid can be used to satisfy demand elsewhere. The network serves the majority of Great Britain and some of the surrounding islands. It does not cover Northern Ireland, which is part of the Irish single electricity market.

The National Grid is a wide area synchronous grid operating at 50 hertz and consisting of 400 kV and 275 kV lines, as well as 132 kV lines in Scotland. It has several undersea interconnectors: an AC connector to the Isle of Man, and HVDC connections to Northern Ireland, the Shetland Islands, the Republic of Ireland, France, Belgium, the Netherlands, Norway, and Denmark.

Ownership

Since the privatisation of the Central Electricity Generating Board in 1990, the grid in England and Wales is owned by National Grid Electricity Transmission. In Scotland the grid is owned by ScottishPower Transmission in the south, and by SSE in the north. Infrastructure connecting offshore wind farms to the grid is owned by offshore transmission owners.

National Grid Electricity Transmission is the transmission system operator, responsible for operating the grid across the whole of Great Britain, while the government-owned National Energy System Operator (NESO) is responsible for managing the electricity market and balancing supply and demand.

History

At the end of the 19th century, Nikola Tesla established the principles of three-phase high-voltage electric power distribution while he was working for Westinghouse in the United States. The first use of this system in the United Kingdom was by Charles Merz, of the Merz & McLellan consulting partnership, at his Neptune Bank Power Station near Newcastle upon Tyne. This opened in 1901, and by 1912 had developed into the largest integrated power system in Europe. The rest of the country, however, continued to use a patchwork of small supply networks.

In 1925, the British government asked Lord Weir, a Glaswegian industrialist, to solve the problem of Britain's inefficient and fragmented electricity supply industry. Weir consulted Merz, and the result was the Electricity (Supply) Act 1926, which recommended that a "national gridiron" supply system be created. The 1926 act created the Central Electricity Board, which set up the UK's first synchronised, nationwide AC grid, running at 132 kV, 50 Hz.

The grid was created with of cables – mostly overhead – linking the 122 most efficient power stations. The first "grid tower" was erected near Edinburgh on 14 July 1928, and work was completed in September 1933, ahead of schedule and on budget. It began operating in 1933 as a series of regional grids with auxiliary interconnections for emergency use. Following the unauthorised but successful short term parallelling of all regional grids by the night-time engineers on 29 October 1937, by 1938 the grid was operating as a national system. The growth by then in the number of electricity users was the fastest in the world, rising from three quarters of a million in 1920 to nine million in 1938. The grid proved its worth during the Blitz, when South Wales provided power to replace lost output from Battersea and Fulham power stations. The grid was nationalised by the Electricity Act 1947, which also created the British Electricity Authority. In 1949, the British Electricity Authority decided to upgrade the grid by adding 275 kV links.

At its inception in 1950, the 275 kV Transmission System was designed to form part of a national supply system with an anticipated total demand of 30,000 MW by 1970. The predicted demand was already exceeded by 1960. This rapid growth led the Central Electricity Generating Board (created in 1958) to carry out a study in 1960 of future transmission needs.

Considered in the study, together with the increased demand, was the effect on the transmission system of the rapid advances in generator design resulting in projected power stations of 2,000–3,000 MW installed capacity. These new stations were mostly to be sited where advantage could be taken of a surplus of cheap low-grade fuel and adequate supplies of cooling water, but these sites did not coincide with the load centres. West Burton's 4 × 500 MW machines, in the Nottinghamshire coalfield near the River Trent, is an example. These developments shifted the emphasis on the transmission system from interconnection to bulk power transfers from the generation areas to the load centres, such as the anticipated transfer in 1970 of some 6,000 MW from the Midlands to the home counties.

Continued reinforcement and extension of the 275 kV systems was examined as a possible solution. However, in addition to the technical problem of high fault levels, many more lines would have been required to obtain the estimated transfers at 275 kV. As this was not consistent with the Central Electricity Generating Board's policy of preservation of amenities, a better solution was sought. Consideration was given to 400 kV and 500 kV schemes: both gave a sufficient margin for future expansion. The decision in favour of a 400 kV system was made for two main reasons. Firstly the majority of the 275 kV lines could be uprated to 400 kV, and secondly it was envisaged that operation at 400 kV could begin in 1965 compared with 1968 for a 500 kV scheme. Design work was started and in order to meet the programme for 1965 it was necessary for the contract engineering for the first projects to run concurrently with the design. One of these projects was the West Burton 400 kV Indoor Substation, the first section of which was commissioned in June 1965. From 1965, the grid was partly upgraded to 400 kV, beginning with a line from Sundon to West Burton, to become the Supergrid.

In the 2010 issue of the code that governs the National Grid, the '' Grid Code'', the Supergrid is defined as those parts of the British electricity transmission system that are connected at voltages in excess of 200 kV.

The 2.2 GW undersea Western HVDC Link from Scotland to North Wales was built in 2013–2018. This was the first major non-alternating current grid link within Great Britain, although interconnectors to foreign grids already used HVDC.

2020s - Great Grid Upgrade

In the 2020s National Grid announced the Great Grid Upgrade, a series of 17 projects to increase the capacity of the grid to receive supply from offshore sources and to meet increasing demand, such as that from electric cars.

In 2021 a new non-lattice design of electricity pylon, the T-pylon, was built near East Huntspill, Somerset for the new 35 mile Hinkley Point C to Avonmouth connection. In 2023, the National Grid began removing equipment made by China's NARI Technology over national security concerns.

In 2024, the Department for Energy Security and Net Zero established the publicly owned NESO to acquire the electricity system operator license from National Grid plc. National Grid remains the transmission system operator.

Characteristics of the grid

The contiguous synchronous grid covers England (including the Isle of Wight), Scotland (including some of the Scottish islands such as Orkney, Skye and the Western Isles which have limited connectivity), Wales, and the Isle of Man.

Network size

The following figures are taken from the 2005 Seven Year Statement.
* Maximum demand (2005/6): 63  GW (approx.) (81.39% of capacity)
* Minimum demand (2020 May): 15.3 GW
* Annual electrical energy used in the UK is around
* Capacity (2005/6): 79.9 GW (or 80 GW per the 2008 Seven Year Statement)
* Number of large power stations connected to it: 181
* Length of 400 kV grid: 11,500 km (circuit)
* Length of 275 kV grid: 9,800 km (circuit)
* Length of 132 kV (or lower) grid; 5,250 km (circuit)

Total generating capacity is supplied roughly equally by renewable, gas fired, nuclear, coal fired power stations. Annual energy transmitted in the UK grid is around , with an average load factor of 72% (i.e. 3.6×10¹¹/(8,760 × 57×10⁶).

Decarbonisation

Decarbonisation plans in 2020 from the UK government and National Grid initially set a stretch target to be carbon neutral or negative by 2033, earlier than the UK's national target to achieve this by 2050. National Grid also aimed to have the capability to be 'zero carbon' as early as 2025, meaning that if energy suppliers are able to produce sufficient green power, the grid could theoretically run without any greenhouse gas emissions at all (i.e. no carbon capture or offsetting would be needed as is the case with 'net zero'). In 2020, about 40% of the grid's energy came from burning natural gas, and it was not expected that anywhere close to sufficient green power would be available to run the grid on zero carbon in 2025, except perhaps on the very windiest days. Analysts such as Hartree Solutions considered in 2020 that getting to 'net zero' by 2050 would be challenging, even more so to reach 'net zero' by 2033.

There has been sustained progress towards carbon neutrality, with carbon intensity falling by 53% in the five years to 2020. The phase-out of coal has been completed: in 2020, only 1.6% of the UK's electricity came from coal, compared with about 25% in 2015. 2020 also saw the UK go more than two months without needing to burn any coal for electricity, the longest period since the Industrial Revolution. On 30 September 2024, on the closure of the last coal-fired power station, UK electricity became coal-free.

In July 2024, The Royal Academy of Engineering released a report into the progress of National Grid's decarbonisation strategy. The report "Rapid Decarbonisation of the GB Electricity System" stated the government’s mission to provide clean power by 2030 sharply raises the level of ambition from an already challenging 2035 target. A revised strategy in 2024 meant that the UK government now aimed to reach this goal by 2030, advancing from the original target of 2035. This change in delivery date was made possible by recent infrastructure investments, and a proposed £77 billion to enhance the electricity transmission network between 2026 and 2031. Months prior to this, an announcement was made about the creation of Great British Energy, a government-backed renewable energy firm. Its creation, and projects that it would have a minority stake in, would play a large role in reaching the government's 2030 target. Investments of £8.3 billion were planned by GBE in offshore wind, hydrogen power, carbon capture and nuclear power developments before 2030.

The 2030 decarbonisation target has also been made possible by the scaling of capacity in offshore wind, while onshore wind and solar sites have been identified to increase the usage of those sites. Public information programs and campaigns have been introduced to try and change user habits in electricity consumption, which can mean using large sources of power outside peak hours. Reductions in the costs of electric vehicle charging overnight is one such scheme that had large take-up in 2024.

Despite progress, there are still some challenges that remain to achieve carbon neutrality by 2035 and net zero by 2050. Development and the installation of transmission energy infrastructure is essential to achieving these goals. System flexibility is a concern: for example, solar is less effective during long periods of heavy rain, thus other green energy solutions are needed to meet the demand. Should clean energy fail to achieve this flexibility, the British media suggested blackouts could be possible, although the ''Daily Telegraph'' stated in January 2025 that large-scale blackouts remain unlikely. Regulatory reforms and energy storage innovations would also play a major role in ensuring clean energy always provides the grid with enough power.

Losses

Figures are again from the 2005 Seven Year Statement.
* Joule heating in cables: 857.8 MW
* Fixed losses: 266 MW (consists of corona and iron loss; can be 100 MW higher in adverse weather)
* Substation transformer heating losses: 142.4 MW
* Generator transformer heating losses: 157.3 MW
* Total losses: 1,423.5 MW (2.29% of peak demand)

Although overall losses in the National Grid are low, there are significant further losses in onward electricity distribution to the consumer, causing a total distribution loss of about 7.7%. Losses differ significantly for customers connected at different voltages; connected at high voltage the total losses are about 2.6%, at medium voltage 6.4% and at low voltage 12.2%.

Generated power entering the grid is metered at the high-voltage side of the generator transformer. Any power losses in the generator transformer are therefore accounted to the generating company, not to the grid system. The power loss in the generator transformer does not contribute to the grid losses.

Power flow

In 2009–10 there was an average power flow of about 11 GW from the north of the UK, particularly from Scotland and northern England, to the south of the UK across the grid. This flow was anticipated to grow to about 12 GW by 2014. Completion of the Western HVDC Link in 2018 added capacity for a flow of 2.2 GW between Western Scotland and North Wales.

Because of the power loss associated with this north to south flow, the effectiveness and efficiency of new generation capacity is significantly affected by its location. For example, new generating capacity on the south coast has about 12% greater effectiveness due to reduced transmission system power losses compared to new generating capacity in north England, and about 20% greater effectiveness than in northern Scotland.

Interconnectors

There is a 40MW AC cable to the Isle of Man, and a 260km 600MW HVDC cable to the Shetland Islands.

The UK grid is connected to adjacent European electrical grids by submarine power cable

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