National Grid has completed infrastructure upgrades at three of its key substations, installing advanced equipment designed to enhance voltage control and strengthen overall network stability.

The project involved the installation and connection of shunt reactors—high-voltage electrical devices that absorb excess reactive power within alternating current (AC) transmission networks—at the Cottam, Wylfa, and Willington substations. Each individual unit weighs approximately 130 tonnes, measures over seven metres in length, and stands nearly four metres high. The introduction of these reactors will allow for more efficient management of the electricity grid.

The key benefits of shunt reactors include:

• Reliable voltage regulation: Shunt reactors can either inject reactive power or absorb surplus, helping manage voltage on the network.

• Enhanced performance: By stabilising voltage, shunt reactors contribute to improved system reliability and operational efficiency across the network.

• Flexibility: They also play a key role in integrating renewable energy by managing voltage fluctuations associated with variable power flows.

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• Asset protection and longevity: Effective reactive power management reduces electrical stress on system assets such as transformers, switchgear, and cables, helping extend their life and lower maintenance costs.

The National Energy System Operator (NESO) holds the responsibility for managing voltage across the transmission system and maintaining appropriate levels of reactive power. Rising levels of renewable energy generation alongside shifting electricity demand patterns are driving changes in reactive power requirements. National Grid's new reactors are set to play an important role in system management, assisting NESO in minimising overall grid balancing costs for consumers.

The deployment of the equipment serves specific regional functions at each location:

• At Cottam, in Nottinghamshire, the shunt reactor was installed to manage voltage stability following the decommissioning of Cottam Power Station.

• At Wylfa, Anglesey, the shunt reactor will support the North Wales network and aid the Dinorwig to Pentir project—which is replacing infrastructure originally installed in the 1970s and adding additional capacity to the network between Dinorwig and Pentir substation—by maintaining voltage stability.

• At Willington, in Derbyshire, the shunt reactor is being used to support expansion of the substation.

The installation schedule saw the Cottam unit energised in March, followed by Wylfa in April, and Willington coming online in May. These upgrades form part of a broader, substantial investment by National Grid into its transmission network, with £31 billion of investment planned over the next five years to modernise and upgrade its infrastructure.

Paul Gallagher, Operations Director at National Grid, said: "Shunt Reactors may be a lesser-known part of our network, but they play a vital role in ensuring electricity supplies are stable and reliable.

"I would like to thank all of the teams involved in delivering this complex activity, which involves a considerable amount of planning and coordination, both on time and on budget.

"It is just one part of the wider work that we are doing to maintain and upgrade the network, ensuring it is resilient and fit for the future to support growing energy demands."