Feature

Electrical connection systems for offshore windfarms and marine applications


Chris Plant, Mike Foster

It isn't just transmission that needs to be looked at carefully when delivering renewables in challenging environments and special applications. Chris Plant and Mike Foster introduce a project investigating sub-sea electrical and fibre-optic connector technology.

The ambitious plans for the installation of large offshore wind farms raise important questions about what other lessons need to be learnt from the installation of smaller wind farms over the past 7 years. or so

The physical installation of cabling, which has been problematic during a number of projects, is recognised as an area in which improvements must be made to reduce the cost and risk of installing large numbers of turbines in deeper water.

A joint industry project between Tronic Ltd (part of the Expro Connectors & Measurements Division) and the UK's Lancaster University, was established to investigate the potential application of sub-sea electrical and fibre-optic connector technology within the renewables industry.

This research-led project investigated the current state of both the offshore wind industry and tidal/wave energy devices, and showed that connector technology has the potential to revolutionise cable installation operations for offshore wind turbines, and that it should be regarded as an important part of any wave or tidal energy device's development.

The problem with cable installation

The cable installation techniques used during the construction of offshore wind farms are recognised by many people within the offshore wind industry as an area of high risk, with a number of high-profile cable failures due to the J-Tube pull; significant design activity is currently underway in an attempt to reduce the risk of cable damage.

Cabling is also an area that is exposed to significant weather window restrictions, due to the requirement for a number of personnel transfers onto the turbine foundations and the nature of the J-Tube pull, which requires the cable installation vessel to be in close proximity to the turbine foundation.

By changing the process by which offshore wind turbines are connected to the grid, connectors can remove these numerous time- and risk-intensive offshore operations, moving them onshore into a more controlled and safe environment. The remaining operations could be designed to be carried out by smaller remote operated vehicles (ROVs), thus removing the need for large work-class ROVs and divers to be present during the cable installation process.

Systems currently used within the Oil and Gas Industry are not directly suitable for the offshore wind industry, due to the demanding environment in which these connectors operate, however lessons learnt during the development of high power sub-sea electrical connectors can be applied to the development of a system – specifically designed to meet the requirements of the offshore wind industry.

Such a connector would meet the same electrical requirements as the cable, and could be regarded – once installed – as part of the cable. However, if an inter-array cable were to be damaged, its replacement would be greatly simplified by the use of connectors, allowing a cable to be disconnected and replaced without access to the turbine, and a safe operating distance from the turbines.

Remaining offshore operations are simplified with the use of connectors; they allow a greater standoff distance to be established between vessels and turbines and reduce the number of people that must be transferred to turbines during the cable installation process. There is significant interest in a system that can improve the cable installation procedure within the industry, and Tronic are keen to engage with potential users of a connector system to speed the development of a suitable product for the industry.
Cost benefits

The changes to the installation procedure discussed will have a number of benefits, almost all of which have direct financial implications; perhaps the most important to cable installation companies is the reduced exposure to weather windows. By moving operations onshore and the remaining offshore operations away from the turbine foundations, the cable installation process can be completed in a wider weather window.

The ability to use smaller ROVs has a consequential benefit of allowing the use of smaller classes of vessels during cable installation operations, thus reducing the cost of vessel hire, and the losses if a vessel is idle during a period of weather disruption. Further cost reduction is achieved through the removal of the cable pull into the base tower, and the moving of cable termination process (both fibre-optic and electrical) onshore, making them easier, and removing the need for personnel to be sent offshore.
What next for the research?

Connectors developed for the offshore wind industry will bare little resemblance to those used in the oil and gas industry; they will have to be built using volume production techniques and designed for quicker termination, using new techniques not suitable for use in the water depths experienced in the oil and gas industry. They will also need to be value engineered to meet mechanical requirements that differ from the onerous specifications used within the oil and gas industry.

During this process, the input of parties involved in the offshore wind farm industry will be an important factor in determining the success of the connector family developed for this application. The development of a connector for such a different market requires the development of a new knowledge base within Tronic, a development not possible without the input of companies with experience of the industry.

Tidal and wave energy devices could also benefit through the use of electrical connectors, and for many device designs a reliable and capable connector system – both for communications and power transmittal – are often essential for the correct operation of the device.

Within the renewables industry there is a lack of awareness about the availability of connectors, as well as the difference in specification between the connectors currently offered to the offshore oil and gas industry and the connectors that would be required by a tidal or wave energy project. The maturity of the tidal and wave energy device market is a problem at this time; the number of devices manufactured currently is not large enough to justify the development of a connector developed specifically for the market.

This, in turn, forces tidal and wave energy device developers to consider current oil and gas products, the prices of which are a major stumbling block in the path towards adoption of electrical connectors as standard technology in the renewables industry. This is an issue which can only be solved by engagement between a connector supplier such as Tronic (Expro Connectors and Measurements) and a device developer.

About the authors:

Chris Plant is from the UK's Lancaster University, and Mike Foster works for Tronic Ltd (part of the Expro Connectors & Measurements Division).

 

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This article is featured in:
Energy infrastructure  •  Other marine energy and hydropower  •  Wave and tidal energy  •  Wind power

 

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