Reliability analysis of design options for offshore HVDC networks

There is growing interest in developing offshore HVDC networks to connect both offshore wind power and provide interconnection between regions. There are a number of technology, topology and protection options available to developers each with varying levels of design complexity, capital cost and system redundancy. This paper highlights some of the available options and outlines a methodology for investigating the performance of a number of these through an investigation of their reliability against a lifetime of expected fault conditions, principally through a calculation of the expected level of curtailed energy associated with each network design. A number of case studies are investigated to provide a comparison between options including designs with and without HVDC circuit breakers and with varying levels of interconnection and system redundancy. The paper shows that there are potentially significant benefits in terms of reduction in curtailed energy through use of redundant paths for power transmission in the network design and that these can in certain cases outweigh the increased capital expenditure associated with their implementation. An investigation into the need case for HVDC circuit breakers is carried out through a comparison with an alternative sectionalised HVDC network topology and the impact on system reliability is found to be negligible in comparison to the cost of the breakers. Offshore network reliability is also found to be highly sensitive to input assumptions for failure and repair rates and the variability within the results was found to be large meaning it could be difficult to accurately predict the reliability of future offshore network implementations.