This paper details a methodology for investigating the reliability of different offshore grid design options for the connection of offshore wind power to shore. The methodology uses a sequential Monte Carlo-based technique that enables the investigation of realistic offshore phenomena, such as the weather dependency of component repair times. A number of case studies are examined for the connection to shore of a cluster of far offshore wind farms and a cost benefit analysis is performed which compares the capital costs, electrical losses, and reliability of each. There is found to be a clear value in options that have inherent redundancy and alternative protection strategies, which avoid the use of expensive dc circuit breakers, that are shown to be potentially viable. It is also found that low probability, high impact faults, such as transmission branch failures, are a key driver behind overall grid reliability.

Extreme weather events, such as high winds, storms, flooding and temperature extremes, are a major cause of disruption to the supply of electricity to consumers. System operators (SOs) are responsible for ensuring stable real-time operation of large-scale power networks and will act to prevent adverse impacts of such events on consumer supply, contain the extent of supply interruptions that do occur, and restore supply to affected consumers in an efficient and timely manner. SOs will also generally be involved in some way in the long-term planning of the transmission network and generation capacity required to ensure future resilience. In this paper we review some of the strategies adopted by SOs across the globe in ensuring high levels of reliability and resilience to extreme weather, with reference to learning generated from specific recent events. In the face of the potential for both the frequency of such events and for their consequent impacts to increase in the future, we recommend that regulatory control of investment in networks is informed by quantified understanding of the climate-energy interface, including assessment of the potential frequency and impacts of future weather events and shared learning from events experienced by different operators. The statutory role of utilities should include robust assessment of future weather-related risks and appropriate investment in their asset resilience, as well as assisting in the preparedness of supporting agencies to mitigate the impacts of weather-related disturbances on energy consumers.

This paper outlines possibilities for connecting 2.4 GW of power from two separate wind farms at Dogger Bank in the North Sea to the GB transmission system in Great Britain. Three options based on HVDC with Voltage Source Converters (VSC HVDC) are investigated: two separate point-to-point connections, a four-terminal multi-terminal network and a four-terminal network with the addition of an AC auxiliary cable between the two wind farms. Each option is investigated in terms of investment cost, controllability and reliability against expected fault scenarios. The paper concludes that a VSC-HVDC point-to-point connection is the cheapest option in terms of capital cost and has the additional advantage that it uses technology that is commercially available. However, while multi-terminal connections are more expensive to build it is found that they can offer significant advantages over point to point systems in terms of security of supply and so could offer better value for money overall. A multi-terminal option with an auxiliary AC connection between wind farms is found to be lower cost than a full multi-terminal DC grid option although the latter network would offer ability to operate at greater connection distances between substations