Can the cable cope? Delivering power consistently still relies on cable

It’s hardly a secret that one of the biggest challenges facing the developers of data centre facilities is that of power. Most often raised is the issue of grid capacity and the wait time for grid connections. 

Less often is the spotlight turned on the power cable system. Which, given that the entire operation of the data centre turns on the reliability of this element, is perhaps surprising.

Many facility owners are content to leave the specification and procurement of high voltage power cable to the contractors. As a manufacturer, we’d make the case for at least an understanding of the issues involved in achieving the right result at the best cost.

Cable sizing

Connecting high energy use data centres to the grid may involve cable designed to operate at voltages as high as 132kV. It’s essential to design the cable system for the specific power needs of the individual data centre. 

Data centres can run on a single supply circuit designed to handle the maximum power requirements, but this can mean that the systems are running at the top end of their performance window, which could unnecessarily stress the system. Consideration should be given to running a double circuit system. In this arrangement, the power load is shared between the two circuits while also building in a degree of redundancy. In the event of a problem with one circuit the other can handle the full load requirements while repairs are completed.

As the complexity of the data centres escalates, specification of the cables should take into account a reasonable expectation of future power demands. This allows the designer to make the right choice of cable right from the start.

No such thing as a standard cable

Establishing the power requirement is the first stage, but cables for this purpose are not “off the shelf” items. 

With data centre developments increasingly being planned for centres outside of the traditional distribution network, the length of cable run from facility to grid connection can increase significantly. The installation route will need to be planned accurately and the cable manufactured to specific lengths to minimise the number of joints. 

For higher voltage cables the ground conditions will affect the design of the cable itself. Routing that needs to go under a road or river, for example, will need to factor in the derating effect of having to go deeper under the obstacle.

For these reasons, every high voltage power cable will be manufactured to a bespoke design to suit the load and the environment of the route.

This process has been in operation for decades, and each Network Operator will have its own specifications relating to cable design. Each new connection will need to integrate effectively with the existing infrastructure. In certain cases this may mean using specialist joints to connect modern XLPE cable with legacy oil-filled cables.

Only manufacturers approved by the local DNO will be permitted to connect to their network.

The impact of installation

The reliability of the cable system is very dependent on the quality of the installation. Pulling cable through the ducts is itself a skilled operation – the force required to pull the cable must be carefully balanced to its construction. For example, the radius of the bends in the ducts, the height changes over the pull and the conductor material are all factors that need careful consideration to ensure the cable is not overstressed, affecting the long-term performance of the cable.

Cable and accessories are manufactured in a highly controlled environment, with significant quality control processes at every stage of manufacture. Jointing of the accessories, other hand, is down to the skills of the individual operatives working on site, often in less than ideal conditions and under time pressure.

It pays to design the cable system with as few joints as possible, and only to employ jointers who have completed rigorous training programmes specific to the cable and accessory types used in the UK. No cable manufacturer will be able to provide a warranty for complete system unless they also provide the design and jointing services.

Preparing for the worst

A properly designed, expertly installed cable system should perform faultlessly for decades. But, as some recent high-profile circuit failures have demonstrated, there is always the potential for problems.

As a manufacturer, we would always advise on contingency planning from the start. This would include precautions such as:

1. Installing an asset monitoring system alongside the cable. Included as part of the initial installation. The additional cost is minimal, and systems offered by Prysmian such as PRY-CAM will provide consistent real-time monitoring. 

This measures the loading of the cable and identifies any areas of weakness in the cable, joints or terminations, usually in the form of discharge  – potentially in advance of any catastrophic failure. This allows for remedial action and circuit outages to be planned in advance. In a worst-case scenario, such monitoring can assist in locating any fault, allowing for fast resolution.

2. Holding back-up cable and cable accessories in store. Without this precaution it could take weeks for a factory to be able to schedule the manufacture of replacement products to specific design for repairs.

3. Building in redundancy. Most data centres will use battery back-up or independent power generation, and we would also advice using a double circuit for mains power supply for resilience.

Looking to the future

While the energy used in manufacturing and installing power cable will be dwarfed by the operational energy needs of a data centre, there are still significant and positive choices to be made.

The first is to design the cable for optimal efficiency of the whole system. Resistive loss from heavily loaded systems causes energy waste and increases the cost of delivering energy. 

Then there are manufacturing changes that will have a significant impact on the embodied carbon or associated greenhouse gas emissions, and the types and source of the materials used in the cables themselves. 

Prysmian focuses on the use of traceable copper with recycled content and zero-carbon aluminium. The company also has a programme in place to reduce CO2 emissions from our own manufacturing processes.  With a target of net zero emissions by 2035, we are already making progress and have reduced our Scope 1 & 2 emissions by 37% compared to a 2019 baseline. Our aim is for 90% reduction by 2035.

We believe that clean, traceable, renewable electrical power is the resource for the future. Building the infrastructure to support that transition is our field of operation and no organisation has more experience of working with the UK transmission and distribution network than Prysmian.