“DNV Technical Seminar on Electrical Systems for Offshore Wind”: Electrical Components as an integral part of wind farms

During the technical seminar organized on 20 May 2022, experts from the offshore wind energy sector shared their knowledge on grid connections, offshore substations and electrical components. Aleksander Gul, Project Manager at Hitachi Energy Poland Sp. z o.o., presented the key power components in offshore substations on examples of projects from Great Britain, including Hornsea 1 and 2 projects. The cooperation of a static semiconductor reactive power compensator (STATCOM) with a machine compensator was presented. The speaker presented the benefits of such a configuration – including maintaining the short-circuit current necessary for the operation of protections, quick voltage recovery and reducing the voltage drop at distant short-circuits. These elements are responsible for dynamic voltage regulation and active power supply at the point of connection of the offshore farm to the National Power System. During the presentation, the improved STATCOM with energy storage and new components were also shown.

Frank de Wild, Principal Consultant at DNV, addressed the topic of electric cables and their long-term current carrying capacity. The speaker highlighted the disadvantages of currently used methods of cable cross-section selection, such as lack of the variability of cooling conditions, an increase in ambient temperature surrounding the cables plunged in the seabed, or deterioration of heat transfer due to organisms covering the surfaces of exposed cables. All these factors mean that currently cable connections are not designed optimally. As a result, cross-sections can be oversized which affects the cost of the cable, but underestimating the cross-section can result in premature failures and even greater losses for the operator.

“The environment has a much greater impact on, say, these limitations than the power cord itself, so controlling and understanding the cable environment leads to a real impact and understanding of current ratings”, de Wild said.

Before laying the cables, it is crucial to research the connection routes and their proper preparation. Factors such as ambient temperature, cable burial depth and heat resistance must be taken into account. Moreover, different parameters of a cable change with its length. De Wild provided an analysis of the cumulative probability of a thermal bottleneck.

A crucial aspect is to determine the measurement errors of the parameters of the installation environment for power cables. The measurement errors in tests performed in offshore conditions can be large, he noted. Companies do not always analyze or take under consideration these errors when they occur, and this is crucial when considering the variability of factors within the cable.
In an interview with the participants of the seminar, it was emphasized that the costs related to cables (e.g. potential repairs) can be reduced by the appropriate design of the cable line. The design should include the analysis of the cable route, cooling conditions and other factors that may affect its long-term load capacity.