Beatrice Lang
The National Grid is a high-voltage electric power transmission network that supports the UK's electricity market. It connects power stations and major substations, allowing electricity to be distributed from areas of generation to areas of demand. The National Grid company owns and operates the transmission systems, ensuring electricity is delivered safely and reliably across the country. The network consists of over 7,000 kilometres of cables, 90,000 pylons, 346 substations, and 1,500 kilometres of underground cables. It serves the majority of Great Britain and some surrounding islands, excluding Northern Ireland. The National Grid is responsible for maintaining voltage, frequency, and reserve power levels, ensuring electricity is transmitted efficiently and stably.
| Characteristics | Values |
|---|---|
| Network | High-voltage electric power transmission network |
| Area covered | Great Britain, including England, Scotland, Wales, and some surrounding islands |
| Exceptions | Northern Ireland |
| Frequency | 50Hz |
| Voltage | 400 kV, 275 kV, and 132 kV lines in Scotland |
| Number of points of generation | Nearly one million |
| System operator | National Grid Electricity Transmission |
| Electricity System Operator | Maintains voltage, frequency, and reserve power levels |
| Distribution Network Operators (DNOs) | 14 regional companies delivering electricity at a lower voltage to homes and businesses |
| Power sources | Wind, solar, decentralized power sources |
| Power losses | Total distribution loss of about 7.7% |
| Power flow | Average of about 11 GW from the north of the UK to the south |
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What You'll Learn
The National Grid's role in electricity transmission
The National Grid is the high-voltage electric power transmission network in Great Britain, supporting the UK's electricity market. It connects power stations and major substations, ensuring that electricity generated anywhere on the grid can be used to meet demand elsewhere. The network covers England, Scotland, Wales and several surrounding islands, but does not include Northern Ireland, which has a separate electricity system.
The National Grid is made up of high-voltage power lines, interconnectors and storage facilities, which together enable the distribution of electricity. It is a wide-area synchronous grid operating at 50Hz and consisting of 400 kV and 275 kV lines, as well as 132 kV lines in Scotland. It has several undersea interconnectors, including 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.
Electricity is generated in power stations and transported at high voltages across the UK via the National Grid. Before leaving a power station, electricity is transferred at high voltages by using 'step-up' transformers to increase the voltage to around 275,000 V. This high voltage allows for more efficient transmission, as lower currents waste more energy. The National Grid Electricity System Operator (ESO) is responsible for maintaining the correct voltage, frequency and reserve power levels to ensure electricity is transmitted safely and efficiently.
Once electricity reaches a local area, it is delivered at a lower voltage from substations to homes and businesses by Distribution Network Operators (DNOs). These DNOs are separate companies that send electricity from the National Grid to your home, depending on your location. The National Grid is not responsible for issues with the low-voltage distribution networks, which cause most unplanned domestic power cuts.
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How electricity is distributed to homes
The National Grid is the high-voltage electric power transmission network that covers Great Britain, ensuring electricity is delivered safely and reliably across the country. The network connects power stations and major substations, allowing electricity generated anywhere on the grid to be distributed to homes and businesses to satisfy demand.
Electricity is generated in power stations and transported across the UK via the National Grid. Before leaving a power station, electricity is transferred at high voltages of around 275,000 V by using 'step-up' transformers. This high voltage enables the efficient transfer of electrical energy across the grid, as lower currents waste more energy.
The National Grid consists of a high-voltage transmission system that connects power stations to substations and smaller local networks called Distribution Network Operators (DNOs). These DNOs then transport electricity into homes and businesses at a lower voltage. The local distribution system in Great Britain is made up of 14 regional DNO companies, and the specific DNO supplying a home depends on its location.
To ensure the safe and efficient transmission of electricity, the National Grid Electricity System Operator (ESO) maintains the correct voltage, frequency, and reserve power levels. This involves balancing voltage and frequency to prevent unstable electricity that could damage equipment and lead to blackouts. NESO, the National Energy System Operator, is responsible for moving high-voltage electricity from generation sources, such as wind farms, to where it is needed.
The sources of electricity generation in Great Britain have evolved to include more renewable and decentralised power sources, such as wind and solar, alongside traditional large power stations with spinning turbines. The transition to low-carbon energy has resulted in the closure of coal-fired power stations and an increase in renewable power generation, leveraging Great Britain's advantageous position for wind power.
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Voltage and frequency balancing
Voltage is responsible for making electric charges move. By producing reactive power, a generator increases the voltage in the system. Conversely, by switching to absorbing reactive power, the generator can help lower the voltage. This ability to adjust voltage levels is crucial for keeping the grid's electricity safe and efficient.
Frequency plays a pivotal role in ensuring the flow of electricity remains consistent. Electricity in Great Britain operates at a frequency of 50Hz, and any deviation of just 1% above or below this value could cause damage to electrical equipment. Therefore, it is imperative to maintain a stable frequency within a narrow range. Frequency deviations are automatically corrected by generators within seconds, ensuring the electricity supply remains within safe parameters.
The National Grid Electricity System Operator (ESO) is responsible for maintaining the correct voltage and frequency levels. They work closely with power generators and energy storage facilities to provide 'ancillary services', a set of processes that ensure the power system remains stable and balanced. These ancillary services help manage the challenges posed by the increasing integration of intermittent renewable energy sources, such as wind and solar power, which have made the grid more volatile and difficult to balance.
In addition to voltage and frequency regulation, the National Grid also focuses on maintaining system inertia. Inertia helps to maintain stability by acting as stored energy that can be used to dampen sudden changes in system frequency. This inertia is provided by massive turbines spinning at a constant speed, adding resilience to the entire electricity distribution network.
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The role of the National Energy System Operator (NESO)
The National Grid is the high-voltage electric power transmission network that powers the UK's electricity market. It connects power stations and major substations, delivering electricity to homes and businesses.
The National Energy System Operator (NESO) is an independent public body that manages and plans the UK's electricity and gas networks. NESO is responsible for ensuring that the energy system is reliable, efficient, and secure, facilitating the country's transition to net zero.
NESO's responsibilities include real-time system operations and strategic, long-term planning. It provides advice to the government and Ofgem on achieving energy policy goals, including the transition to clean power by 2030. NESO also produces a Strategic Spatial Energy Plan (SSEP) to optimize energy infrastructure and manages the queue of new electricity projects connecting to the grid.
NESO operates as a not-for-profit public corporation, ensuring the delivery of energy to homes and businesses 24/7, 365 days a year. It is the first organization in Great Britain to plan and operate the entire energy system, including electricity and gas system planning.
NESO is committed to supporting its customers and providing the necessary service and support. It offers a dedicated customer support team and a help centre with access to frequently asked questions. NESO also provides transparency through its carbon intensity dashboard and app, allowing users to track the energy mix and monthly energy generation from various sources.
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Power losses and constraint payments
The National Grid is the high-voltage electric power transmission network that supports the UK's electricity market. It connects power stations and major substations, ensuring that electricity generated anywhere on the grid can be used to meet demand elsewhere. The network covers most of Great Britain and some surrounding islands, excluding Northern Ireland.
Power Losses
Although overall losses in the National Grid are low, there are significant further losses in the onward distribution of electricity to the consumer, resulting in a total distribution loss of about 7.7%. Losses differ depending on the voltage at which customers are connected. For high-voltage connections, total losses are about 2.6%, while medium and low-voltage connections experience losses of 6.4% and 12.2%, respectively.
Power losses in the generator transformer are accounted for by the generating company, not the grid system, and do not contribute to grid losses. However, as the sources of electricity generation have expanded to include more renewable sources, such as wind and solar, the grid has faced challenges in effectively incorporating new technologies into legacy systems.
In the context of power sector finances, persistent financial losses have been observed in state-owned power distribution companies, or "discoms," due to structural issues and outdated contracts with generation companies. Delayed subsidy payments from state governments and suboptimal tariff recovery have also contributed to cash flow issues and debt accumulation for discoms.
Constraint Payments
Constraint payments are made when generators above a certain size are instructed by the National Grid to reduce their electricity output due to a lack of transmission capacity, a shortfall in demand, or unexpected excess generation. These payments compensate generators for the reduction in their generation and are considered more cost-effective than building new infrastructure to move power.
Constraint costs have been rising, particularly with the increasing integration of zero-carbon generation in the north and east of Britain. In 2024, constraint costs exceeded £1 billion, with 76% relating to payments to gas generators due to systemic grid limitations.
One proposed solution to address constraint costs and support the Clean Power Plan is to redesign the electricity market around zonal pricing, splitting the market into zones that correspond to transmission constraint boundaries. This approach aims to reduce the price of electricity during constraint events and drive the utilisation of wasted wind power.
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Frequently asked questions
The National Grid is the high-voltage electric power transmission network for Great Britain, supporting the UK's electricity market. It connects power stations and major substations, ensuring that electricity generated anywhere on the grid can be used to satisfy demand elsewhere.
The National Grid distributes electricity through a high-voltage transmission system, connecting electricity from power stations to substations and smaller local networks, called Distribution Network Operators (DNOs). These DNOs then transport electricity to homes and businesses. The voltage and frequency of electricity must be balanced and kept uniform to avoid unstable electricity that could lead to blackouts.
NESO (National Energy System Operator) is responsible for moving high-voltage electricity from generation sources, such as wind farms, through the system to where it is needed. NESO manages the electricity market and balances supply and demand.
Electricity is generated at power stations and stepped up to high voltages of around 275,000 V for efficient transportation over long distances. When electricity reaches homes and businesses, it is stepped down to 230 V.
