Grid-ready data centres

Grid-ready data centres

Data center protection

How high-resistance grounding keeps data centres online

In December 2025, the UK’s National Energy System Operator (NESO) announced the results of its major overhaul of the UK’s grid connection process, removing speculative schemes and introducing a readiness-based system. While this affects all electricity projects, it raises the bar for data centres, which must now demonstrate gridfriendly behaviour from day one. Here, Mike Torbitt, managing director of resistor manufacturer Cressall Resistors, explains how neutral earthing resistors (NERs) support resilient, grid compatible operation.

Data centres have been recognised as Critical National Infrastructure (CNI) since September 2024, placing them on “an equal footing with water, energy and emergency services systems”. While this recognition is invaluable to scaling capacity, NESO’s reforms add a new layer of complexity.

The Connections Reform context

Under the Connections Reform, NESO now prioritises “first ready and needed,” replacing the former firstcome, firstserved approach. Many transmission-connected demand projects – including data centres – have been placed into firm capacity blocks with connection dates extending to 2035, reflecting a more realistic delivery timeline than the prior ambition to connect the full pipeline by 2030. In this context, fault management and predictable, grid friendly operation become prerequisites for connection.

The readiness framework is evidence based. To secure a firm offer, developers must prove deliverability and true grid readiness — not just on paper, but through design maturity, risk controls and credible delivery plans. A robust power and protection strategy is therefore critical, showing the facility will behave predictably during network disturbances and will not trigger unnecessary disconnections.

What is high-resistance grounding?

One mechanism central to grid friendly design is highresistance earthing, also known as highresistance grounding (HRG). Although industry benchmarking shows overall outages are declining, Uptime Institute data indicates power remains the leading cause of impactful incidents when failures do occur, cited by 54 per cent of operators surveyed would be more accurate to the Uptime Institute’s methodology.

In HRG systems, the transformer or generator neutral is connected to earth through a high value resistor. By introducing resistance, HRG limits single line to earth fault current to a small, controlled value — typically a few amps at low voltage or tens to hundreds of amps at medium voltage. The outcome is that a first earth fault becomes an alarm only event rather than an immediate trip, enabling continued operation while teams quickly locate and clear the fault.

This approach avoids the drawbacks of other schemes. Unlike solid earthing, it prevents very high singlelinetoearth currents and the associated incident energy, and unlike ungrounded systems, it keeps the neutral referenced, suppressing transient overvoltages and making faults easier to locate. 

Proper HRG design sets the resistor so the permitted fault current is above the system’s capacitive charging current, yet low enough to reduce equipment stress and arc flash energy for single-line-to-earth faults. In data centres, this keeps the first earth fault ‘alarm only’, sustaining critical services while teams rapidly pinpoint the faulted feeder, avoiding nuisance trips across uninterruptible power supply and generator transitions and supporting gridfriendly operation in the highdensity, alwayson environment.

NER data center protection

The critical component

An NER is the enabling component of a HRG system because it connects the neutral point to earth through a precisely selected resistance. By setting the resistance value correctly, the NER establishes the single line to earth fault current and the associated thermal duty so that protection relays can reliably detect a first fault without forcing an immediate trip. This behaviour keeps the system stable during disturbances and allows operators to locate and clear faults while maintaining service continuity.

For data centres, NERs must be engineered to match real world constraints such as footprint, access routes for installation and maintenance, cooling and ventilation needs, and compliance with relevant international electrical standards. Cressall’s designs prioritise ease of maintenance, high thermal performance and long service life so that facilities can run continuously and recover predictably after fault events or tests.

Selecting the right resistor element is central to performance and cost. Edgewound coils are suited to higher currents, while grid and wire-wound elements serve other ratings efficiently. Cressall manufactures NERs across essentially any system voltage and initial fault current requirement, with rated durations ranging from a few seconds to continuous duty, so that specifications can align with the site’s protection guidelines and operational objectives.

Now that grid connections have been reprioritised, well‑specified NERs within HRG schemes make the first earth fault a managed, alarm‑only condition, keeping services online, demonstrating grid‑friendly behaviour and helping ensure data centre designs do not delay connection.

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Keeping the UK’s most ambitious energy project afloat

KEEPING THE UK’S MOST AMBITIOUS ENERGY PROJECT AFLOAT

DBRs for tidal power projects

HOW RESISTORS ENSURE RELIABILITY IN TIDAL PROJECTS LIKE MERSEY TIDAL POWER

The UK’s clean energy transition is set to take a major leap forward with the Mersey Tidal Power project, a proposed development that could become one of the largest in the world. But what challenges does a project of this scale present for electrical infrastructure? This article explores how resistors can help stabilise the grid and extend component lifespan to ensure the long-term success of tidal projects.

The Mersey Tidal Power project is one of the UK’s most ambitious renewable energy projects to date. Inspired by successful tidal range developments such as La Rance in France and Sihwa Lake in South Korea, it aims to replicate the long-term viability of tidal power on an even larger scale. Using a barrage-style turbine array to harness the immense power of the river Mersey’s tides, the development could generate up to one gigawatt (GW) of clean energy. However, despite its promise, the scale and ambition of the project raises several challenges that require careful consideration.

STABILITY AND RELIABILITY DEMANDS

Unlike other renewable sources, tidal power generation follows a predictable pattern, being governed by the lunar cycle. However, tidal energy still experiences variations in output due to the changing intensity of tidal flows. Managing these fluctuations, particularly at such a scale, requires highly efficient electrical infrastructure.

Any variation in energy production needs to be carefully managed to prevent fluctuations from causing inefficiencies or disruptions in power transmission. Without this precise control, power surges or dips could destabilise the grid, undermining the reliability of the entire energy network.

The Mersey Tidal Power project’s sheer scale also introduces technical demands beyond standard renewable installations. With an expected operational lifespan of over 120 years, all components — especially electrical systems — must be designed to withstand extreme marine conditions. Saltwater corrosion and high mechanical stresses from strong tidal currents place exceptional demands on electrical equipment. Ensuring system longevity requires components that are not only resilient but also capable of maintaining performance over decades of operation.

ANCHORING TIDAL POWER

The success of large-scale tidal energy projects depends on a responsive and reliable electrical system. Dynamic braking resistors (DBRs) play a key role by absorbing excess energy during peak tidal flow. When tidal currents are at their strongest, turbines can generate more electricity than the grid can immediately use. DBRs convert this surplus electrical energy into heat, safely dissipating it to prevent voltage spikes or overloading transformers. By smoothing out power delivery, they help maintain a consistent and reliable supply of electricity, ensuring that tidal energy can integrate seamlessly with the wider grid.

Beyond grid stability, resistors also protect the physical infrastructure of the turbines. Rapid changes in water flow, such as shifts between ebb and flood tides, can create sudden torque variations on turbine blades and drive systems. DBRs help regulate these mechanical stresses by slowing the turbine’s rotational speed in a controlled manner, reducing wear on bearings, shafts and other moving parts. 

Given the vital role that resistors play in tidal power generation, their durability in harsh seawater is essential. High-quality marine braking resistors are engineered to withstand the extreme conditions of tidal power systems, including corrosion, heat and mechanical wear. Designs often incorporate sheathed mineral-insulated elements to protect against physical damage and environmental degradation, alongside marine-grade stainless steel to resist saltwater corrosion. These durable materials allow resistors to maintain peak performance for decades, even in the demanding conditions of tidal power projects.

While the scale of the Mersey Tidal Power project raises technical challenges, the proposed development is a bold testament to the UK’s commitment to clean energy. As the government increasingly supports tidal power as part of its long-term energy strategy, this project could pave the way for widespread adoption of tidal infrastructure. Throughout this transition, resistor technologies are expected to play an important role in ensuring the stability of the grid and the longevity of power generation systems.

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Protecting the backbone of clean energy

Protecting the backbone of clean energy

Protection technology ensures safe, reliable battery storage for renewables

In the UK, the share of electricity generation from renewable sources during the second quarter of 2025 reached a new record level of 54.5 per cent of all generation, according to the Department for Energy Security and Net Zero. But as we shift closer to a net-zero energy system, it becomes critical to have a robust storage solution to harness the energy we produce. Here, Mike Torbitt, managing director of Cressall, explores the technology behind battery energy storage systems (BESS).

The Government’s Clean Power 2030 Action Plan, introduced in December 2024, looks to ensure that clean sources produce “at least as much power as Great Britain consumes in total” and “at least 95 per cent of Great Britain’s generation”. Achieving this will rely on a blend of offshore wind and solar energy deployed at scale.

But this transformation hinges on flexibility. As wind and solar dominate, BESS is becoming the backbone of grid stability, absorbing excess renewable energy and releasing it during demand peaks. Lithium-ion technology leads the way here, comprising 95 per cent of UK BESS projects, thanks to its rapid response and scalability.

The BESS landscape

Higher renewable penetration has driven demand for energy storage. As of September 2025, RenewableUK reports 1,943 active battery storage projects in the UK, with 6.8 gigawatts (GW) of operational capacity — a 509 per cent increase since 2020.

Even larger projects are underway. Tillbridge Solar in Lincolnshire will deliver 1.5 GW of solar PV and three GWh of BESS, while Pembroke Battery in Wales will become the UK’s largest storage facility when construction begins in early 2026.

These assets will provide fast frequency response, peak shaving and renewable firming. Their success, however, depends on safe, reliable integration into medium-voltage (MV) grids. Systems typically connect at 6–36 kV, where grid code compliance, fault studies and earthing design are critical. Without robust protection, the promise of storage could falter under grid physics.

MV challenges

MV grids are faultenergy rich environments. In solidly earthed MV systems, a singlelinetoground fault can drive very high currents, imposing severe thermal and mechanical stress on stepup transformers, converter valves and switchgear. 

For BESS, rapid dispatch and high-power flows amplify risks such as inrush currents, transient overvoltages and earth faults escalating in milliseconds, posing compliance and protection challenges under the GB Grid Code. Without controlled earthing, fault magnitudes can exceed clearing times and equipment limits, risking outages and costly repairs.

As grids add high voltage direct current (HVDC) links to ferry offshore wind and remote solar, and as BESS ties into converter stations or MV collectors, abnormal conditions like DC faults reflected into AC neutrals demand predictable neutral behaviour. Limiting ground fault current is essential to maintain converter transformer integrity and prevent cascading trips.

Making BESS safe

This is where neutral earthing resistors (NERs) do the quiet, but crucial work. By inserting a defined resistance between the transformer neutral and earth, an NER limits earth fault current to a level that protection relays can detect and clear selectively, without tripping the entire plant.

NERs prevent transformer insulation damage, reduce arc flash hazards, minimise voltage stress on equipment, enable controlled fault detection and isolation and maintain system stability during fault conditions. Cressall supplies NERs tailored for MV and HV duty in renewables and storage, with engineering guidance that highlights how DC and AC NERs protect converter transformers and maintain system integrity during abnormal events — requirements that map directly to MVconnected BESS. 

Every Cressall NER is designed to IEC and IEEE standards, factory tested under fault current conditions and built with stainless steel elements for outdoor durability. They are rated for continuous operation in harsh environments, ensuring reliability in demanding renewable installations.

In practice, this means fewer catastrophic stresses on transformer windings and converter components, better adherence to grid code protection settings and smoother interconnection approvals. 

The UK is reshaping its energy system, but success depends on more than megawatt-hours. Behind every project is a layer of protection technology that keeps the grid stable. As the UK races toward Clean Power 2030, NERs are foundational, turning unpredictable faults into manageable events, making MV-connected BESS bankable and resilient.

To learn more about Cressall’s NERs for BESS applications, please visit the website

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Wasted wind and the UK’s curtailment challenge

WASTED WIND AND THE UK’S CURTAILMENT CHALLENGE

Why clean energy goes unused and how technology can help

According to the Times, in 2025 UK households effectively paid £810 million for Scottish wind farms to stand idle, highlighting a growing problem in the country’s renewable energy sector. Here, Mike Torbitt, managing director of Cressall, explores the causes behind the UK’s wind curtailment issue and explains how resistor technology can help stabilise the grid and make the most of renewable energy.

How curtailment works

Curtailment happens when wind farms are asked to reduce or shut down generation of electricity, even where generation conditions are optimal. The reason is rarely the turbines themselves. It usually happens when the grid cannot take in the amount of power being generated, or there is no demand for it at that time.

On paper it sounds like an occasional technicality. In practice, it has become a regular issue of the UK’s energy system. Every time turbines are switched off, revenue is lost, bills rise and carbon savings are wasted. For consumers, that means paying for energy that never reaches their homes — a frustration that grows as wind makes up more and more of the power mix.

Most of the UK’s wind power comes from Scotland, where land and wind resources are plentiful. The challenge is transporting that electricity to where it’s needed. Transmission south of the border is limited so when output surges, the system cannot always absorb it. In June 2025, the Financial Times revealed that wind farms were paid to switch off 13 per cent of the time they could otherwise have been producing. 

The costs are also mounting. Operators are compensated for shutting down, but those payments ultimately come from household energy bills. Environmentally, the waste is even starker: each megawatt-hour curtailed means another load of carbon that could have been avoided — the equivalent of the electricity used by around 330 homes. 

The scale is particularly clear in Scotland: according to Recharge News, the nation’s grid-constrained producers curtailed 37 per cent of their output in the first half of 2025. That amounts to about 1.5 terawatt-hours of lost clean energy — enough to power 1.2 million homes for a year. 

How to capture lost power

There is no single solution to preventing curtailment, but there are possible ways forward. New grid infrastructure and cross-border interconnectors would allow Scottish surplus wind to reach areas of higher demand. Vast storage schemes, from factories producing batteries to pumped hydro, would be capable of soaking up excess power and delivering it at the appropriate moment. More advanced control systems would also even out the peaks and troughs of supply and demand. 

Protective technologies have an important function in surge control in renewable energy. Resistors act as thermal valves for high-voltage systems, dissipating excessive electrical power as heat to prevent overvoltage or equipment loss. Dynamic braking resistors (DBRs), for example, can be connected to generator circuits or inverters to absorb sudden spikes in power output, helping to stabilise voltage and maintain grid frequency.

Elsewhere, neutral earthing resistors (NERs) limit fault currents in high-voltage direct current (HVDC) systems and protect transformers and switchgear against thermal and mechanical stress. Properly engineered NERs ensure that the system can safely tolerate transient faults without triggering unnecessary trips, maintaining grid reliability and stability.

By incorporating DBRs and NERs, energy systems can safely handle the variable nature of renewable generation, absorbing or redirecting excess energy rather than wasting it. This improves overall grid efficiency and allows a higher proportion of renewable energy to reach consumers.

Curtailment is not just about wasted energy. It’s about missing the opportunity to cut carbon, lower bills and strengthen the UK’s energy security. With the right infrastructure and the right protective systems in place, the country can capture far more of the renewable power already being produced. 

Cressall provides expert NER and DBR resistor solutions to help grids safely manage renewable energy surges. For more information and to view technical datasheets, visit the website.

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