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66kV cables: catalysing industry for a step-change to higher voltage cables

In 10 years, the Offshore Wind Accelerator (OWA) has run over 150 projects supporting innovations that have led to both a significant reduction in the cost of energy and risk, whilst making offshore operations safer. To mark this milestone in R&D collaboration, we have selected 10 high impact innovations to showcase the breadth and depth of the programme.

66kv-cables

Electrical systems is one of the research areas of the OWA. It has had significant success through championing the use of higher voltage cables carrying 66kV of electricity.

Previously, the cables used to connect each turbine in a wind farm to the offshore substation, known as inter-array cables, carried 33kV.

With wind turbines becoming increasingly larger and offshore wind farm projects growing bigger, the use of 33kV was becoming a limiting factor. A large number of cable strings are required to enter each offshore transformer, which means the total length of cable required is greater. More cabling means higher cost. Not only that, but the longer the cable and lower the voltage, the greater the potential for electrical system loss, leaving considerable potential to make the whole system more efficient.

Higher voltage cabling gave the potential to connect wind farms with fewer cable strings, reducing both the cost and the total electrical system loss.

The OWA decided to intervene.

Our early conversations established that moving to a higher voltage cabling would mean fundamentally changing nearly all the electrical components of the system and redesigning all the key technical components, such as the cables, switchgear, transformers, wind turbine structures and offshore substations.

We did a cost-benefit analysis and a detailed qualitative comparative study of the supply chain, health and safety, and operation and maintenance considerations, and developed a roadmap to take the technology from conception to commercialisation.

Today, the 66kV cabling carries double the power with only a small increase in upfront cost. It connects more turbines than the 33kV could, loses less electricity throughout the system, and saves on installation costs.

Increasingly, the industry was agreeing that higher voltage cables were needed, however suppliers could not develop new cables without certainty of use, and developers needed new cables tested and validated before stating whether they would use 66kV.

To combat this chicken-and-egg scenario we launched a competition and invited applicants to develop 66kV cables at a competitive cost.

Four designs made it through, developed by JDR, Nexans, and Prysmian. We tested them, qualified them, and brought them to market readiness. The first 66kV cable became commercially available in 2016.

This work – of staking time, resources, and energy investigating an as-yet-unproven technology, encouraging and incentivising independent organisations and researchers to work on it, and seeing it through to the market was only made possible by the OWA.

Today, the 66kV cabling carries double the power with only a small increase in upfront cost, which helps to make the windfarm as a whole cheaper in the long run. It connects more turbines than 33kV could, loses less electricity throughout the system, and saves on installation costs because less cabling, transformers and fewer substations are required. In short, it makes offshore wind cheaper and more efficient. The OWA made this happen faster than it otherwise would.

This article is part of 10 years, 10 innovations: A summary of the impact of the Offshore Wind Accelerator

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