Data centres, battery storage and large industrial sites are increasingly connecting at extra high voltage, where a single project can rely on a dozen organisations working to one programme. Ben Croxford, chief operating officer at Eclipse Power, explains why bringing in experienced engineering support early has become critical to delivering EHV projects.

 

The UK is re-engineering its power transmission network to meet the grid’s biggest challenge – and its greatest opportunity – since it was first built. At once, the electricity network needs to step up to support the clean power we need to displace fossil fuels across transport, heating and industry, and scale to enable the investment and growth opportunities that come with decarbonisation and the expansion of AI.

 

The scope of the grid reinforcements and the number of projects being proposed have together contributed to skills and supply chain shortages, along with well-publicised grid connection queues. But the nature of the projects awaiting connection has changed almost as rapidly as the queue itself has formed.

 

Developments such as hyperscale data centres, port electrification projects and utility-scale renewable and storage installations need grid connections measured in tens or even hundreds of megavolt amperes (MVA). At this scale, energisation usually means connecting to the extra high voltage (EHV) network – above 22 kilovolts (kV) and up to 132kV in England and Wales – or directly to the 275kV and 400kV transmission system. It also means a degree of complexity, and a level of engineering diligence that goes beyond what’s needed at lower voltage levels. Protection design, system studies, outage planning and compliance with network codes all become more demanding, and mistakes take longer and cost more to put right.

 

From projects to programmes

An EHV connection differs from a distribution connection in scale, in risk, and particularly in the number of parties involved. In the UK, a single EHV scheme can depend on the transmission owner, the local distribution network operator (DNO) and an independent distribution network operator (IDNO). In addition, it’s likely to involve independent connection providers (ICPs), planners, landowners, environmental specialists, several contractors and an equipment supply chain. This complexity means that large connections can be less like projects, and more like programmes.

 

That has real consequences for delivery. A customer can have its design complete, its equipment installed and commissioning ready to begin, and still see its energisation date move because a DNO reinforcement or a transmission outage hasn’t lined up with everything else. The earlier a potential clash is spotted, the better the chance of protecting that date, which is why so much of the work on an EHV project is about keeping every party working towards the same milestones.

 

The push to connect sooner tends to add complexity of its own. Developers are phasing their build programmes, accepting flexible or non-firm arrangements, or reshaping the size of their connection to secure earlier capacity. Each of those choices creates new decisions that run through design, commercial agreements and, eventually, operation. Even making the wrong decision on something less obvious, such as whether a site is charged under the common or EHV distribution charging methodology (CDCM or EDCM), can lead to an unwelcome cost years later.

 

The people problem

While lead times for major plant and switchgear remain long across both distribution and EHV work, people are a tighter constraint still. In our experience, most power engineers build their careers in distribution and work their way up, so fewer people have deep experience at the highest voltages. One specialist recruiter reports employers competing for ‘a relatively small pool of experienced professionals across HV engineering’, with EHV design, protection and commissioning roles all in demand. Energy & Utility Skills expects the power sector to need almost 157,000 new entrants by 2030. A successful EHV programme needs the right designers, project managers, commissioning engineers and operators across its whole life.

 

Hyperscale data centres show just how complex EHV projects can become. A campus might need only a fraction of its eventual capacity on the day it opens, with the rest following over several years as data halls are built and fitted out. That means designing the network for its end state, while energising it in phases – each one relying on contracted dates, plant deliveries and outages all staying to schedule. With Ofgem proposing commitment fees and progress milestones for data centre connections, a phase that slips could soon carry consequences well beyond a delayed opening.

 

Given the competition for grid connection, many of these sites may be designed and built on private networks that share a single grid point among multiple users. Data centres, industrial tenants, on-site battery storage and generation can all sit behind one connection, which raises questions that go well beyond the sizing of cables and transformers. Multi-tenant sites need clarity on who owns and operates the network, whether it’s adopted by an IDNO or run privately under a licence exemption, how each user is metered and charged, and how the whole system is protected.

 

Add the redundant supplies that data centre operators usually expect – which can mean more than one connection point and yet more parties to coordinate – and the task scales well beyond simply connecting a customer. In our experience, we’re often asked to support developers to start off with a full understanding of options and how complex they can become, as decisions made at this stage can be the hardest to unpick once construction is underway.

 

What engineering expertise brings

It’s here that EHV engineering expertise shows its value – long before anyone breaks ground. Experienced partners can understand how the customer’s business works commercially and operationally, and what it needs from the connection. They’ll ask questions such as whether speed is worth more than capital cost, whether the customer wants to own the asset, and how much risk it can carry. The options can then be compared honestly, with clarity on who carries which risks.

 

From there, expertise shows up in value engineering that challenges the design and specification, so customers pay only for what they need without compromising safety or reliability. A partner experienced in EHV can help manage the relationship with DNOs, transmission owners and the National Energy System Operator (NESO), dealing with the complexity that often causes EHV projects to stall.

 

On one transmission-connected scheme, for example, that has meant coordinating between several contractors and the transmission owner, including a modification application and a letter of comfort. On a data centre project, the work can extend well beyond electrical design to resolve considerations such as the cable route and landowner easements. Partners whose engineers have worked on previous EHV schemes, or at DNOs, NESO and National Grid, are often best placed to keep those conversations moving. That’s certainly been our experience at Eclipse, where many of the team have come from these backgrounds.

 

The benefits of expertise don’t stop at energisation. Where an IDNO adopts a network, it can own, operate and maintain it for the long term and pay an asset value back to the customer, which reduces its upfront capital and means it doesn’t need to staff or contract high voltage operations itself. Once the network is live, condition-based inspection lets the operator gather performance data without taking assets out of service, so intrusive maintenance happens only when it’s needed. Careful outage planning helps too: on a 132kV battery storage network, for example, the operator can time its own work to coincide with a pre-planned upstream DNO outage so the customer is affected only once. Meanwhile, innovations such as drone thermography to find hot joints and verify repairs can help keep maintenance proactive and reduce the risk of unplanned outages.

 

Bring the expertise earlier

For developers moving into EHV, our advice is to involve experienced engineering support as early as possible, ideally before the connection strategy is fixed. Decisions made at offer stage shape design, delivery and operation for decades, and the assumptions agreed then should carry all the way through to the connection and interface agreements, the handover into operation, and the tariff and metering arrangements on day one.

 

Looking further ahead, we see a strong case for connecting more very large loads directly from transmission voltage, with independent and private networks playing a bigger part in delivery. Regulation is starting to reflect this. Following its call for input earlier this year, Ofgem said in June that it is prioritising work on an independent transmission owner (iTO) licence, building on the established IDNO model. It plans to consult on initial proposals this autumn, and the government has since committed to reforming the rules on self-build connections. The details are still to be settled, but it’s an area where practical EHV experience will count for more, not less.

 

The UK’s energy transition will bring more large, technically demanding connections, reflecting exciting prospects for the developers behind them. The projects that connect on time and on budget will be those that appreciate the complexity of EHV work, and build in the right expertise from the very start.