The design and installation of offshore wind farms is one of the most exciting and dynamic areas of engineering, with innovation helping to address energy capacity requirements as part of a diverse mix of traditional and renewable developments.
However, unlike traditional power generation assets, offshore wind farm operators do not always have the full range of capabilities to deal with an unexpected high voltage (HV) cable fault.
The subsea (below ground) location of export cables means that the risk profile associated with export cables can sometimes be underestimated, and cables are often expected to faultlessly run for decades, however failures unfortunately do happen and therefore it is vital to consider how to effectively manage a cable failure should the worst happen.
By their very nature, wind farms are located in harsh environments where extreme weather and damp and salty atmospheric conditions inflict significant stress on the components that can ultimately result in an export circuit failure. As mentioned, the subsea location of the cables also adds to the challenges of managing these assets in addition to unknown factors such as cable design, installation damage or the impact of third party vessels affecting cable integrity.
Despite meticulous attention to detail invested during the installation process, wind farms can still experience cable faults, and without a contingency plan in place it can be difficult to address the fault quickly, as it is impossible to predict when a fault may happen.
For offshore wind farms, the challenges of managing subsea cables makes such failures even more damaging to business. An unexpected cable fault could lead to power generation revenue losses amounting to hundreds of thousands of pounds per day. When this significant loss of revenue is considered alongside the cost of reactive repairs, not to mention the damage to an operator’s reputation, a lack of contingency planning to underpin continuous operation of an offshore wind farm can come at a very high price indeed.
Cable concerns
While the design life of subsea cables anticipates a cable failure just once every 30 years, export cable faults have risen by an alarming 500 per cent over the past 12 months. Contingency planning for such failures has never been so important and business critical for all stakeholders.
There is little clarity on the cause of these failures, and, therefore, little reason to suppose that this is a problem that is going to be resolved any time in the near future. EDS has been involved in several subsea cable repairs in both North Sea and Irish Sea offshore locations over the past twelve months. Amongst these was a pre-emptive fix when a potential failure was recognised thanks to remote monitoring; and this demonstrates a considered approach to contingency planning from the operator, which prevented the risk of an unplanned outage, potentially saving hundreds of thousands of pounds in downtime.
HV health checks
Contingency planning ideally starts with the design process, however some operators aren’t aware of the effective monitoring that can also be put in place post installation, which can ensure that any such failures are identified and located immediately thereby reducing the potential loss of generation revenue.
A coherent contingency plan and sustained partnership with a remote-monitoring and asset management engineering specialist is vital for offshore wind farm operators because of the variety of faults that can occur. Onshore export cables may need to be accessed quickly to help locate faults or carry out repairs, so good relationships with the relevant local authority and landowners is vital.
Other potential export circuit faults include cable sealing end failure, surge arrestor failure and cable termination failure, all of which must be factored into a contingency plan that includes regular condition assessments and maintenance regimes.
A streamlined solution
Whilst the risks associated with cable failures have huge revenue and power generation implications, there are solutions and preventative actions wind farm operators can take. By anticipating and preparing for a failure, you’re already in a position to act immediately in an emergency situation.
Technology is now available which can permanently monitor export circuits remotely to ensure a quicker response to any cable failure, as engineers can accurately pin-point where the fault lies if the worst should happen. Knowing where the fault is located immediately saves time and therefore can help minimise consequential loss.
A strategic spares assessment which includes checking the correct storage of all perishable items, is vitally important should the unexpected happen. Spare cable and joints should be stored safely and securely on site with regular inspections to ensure that they are still fit for purpose so that work can be carried out promptly as and when required following a failure. Any spare components and materials must then be replaced in the store as part of ongoing contingency planning.
An alternative solution offered by EDS Group is the innovative Universal Joint, technology which has been engineered in-house. The Universal Joint enables wind farm operators to invest in a permanent universal repair component as part of their contingency planning; ensuring that a versatile and robust engineered solution is available quickly in the event of cable failure. Such failures would normally entail time consuming and expensive repairs to the cable infrastructure, with any delays in specifying and securing supply of the correct components prolonging outage periods and further increasing costs.
Launched at a VBMS event on the future of sustainability in Rotterdam earlier this year, the Universal Joint was widely praised as an innovative solution to a common problem of cable availability, with typical lead times for subsea cable joints often as much as six months.
The new joint has been designed to connect varied cable sizes, as well as cable from different manufacturers, with an off-the-shelf component with no design changes. It will provide a fast install solution that can be completed in less than 48 hours, including base electrical and optical testing to take advantage of small weather windows.
The compact unit will also dramatically reduce the number of components that wind farm operators will need to store for emergency repairs, while facilitating much faster remediation works.
Working with an engineering team that has proven expertise in high voltage management during offshore wind farm installation and maintenance is, of course, critical to the success of the project both during the build phase and throughout its operation. Working with a partner that can offer an interdisciplinary approach to consultancy, installation, HV safety, asset management and fault monitoring ensures a joined-up approach that considers the lifecycle requirements of the offshore wind farm’s HV assets, ensuring that optimum performance is built into all aspects of its operation.
These relationships should be embedded in the contingency plan, which must be communicated effectively across the organisation, so that all members of the team know exactly who to call in an emergency. This helps operators easily source materials quickly by having agreements in place with suppliers and other relevant parties, so you’re not waiting weeks for legal teams to confirm negotiations between contractors and suppliers. This is extremely important to ensure that vessel operators are safe in the knowledge that they can mobilise engineers on site as legalities have already been confirmed.
Working with a trusted engineering contractor can give operators access to innovative technology and in the event of a cable failure, reduces response times as well as the costs of unexpected downtime.
Looking ahead
A high level of advanced engineering goes into the development and installation of wind farms and turbines, resulting in clean energy for millions of households– but if a cable fails, power generation from renewable energy is inevitably curtailed.
As an industry we need to move towards reducing the LCOE (Levelised Cost of Energy), meaning, we have to think about the long term costs of operating our wind farms rather than just the immediate costs. The financial benefits of a full site review and robust contingency plan can often be overlooked.
An effective plan can help to reduce the operational and financial implications of faults, which makes it a vital part of the commercial strategy for any offshore wind farm.
ABOUT THE AUTHOR
Ryan Henderson is Director of EDS Group.
FURTHER INFORMATION
http://www.edshv.com/