Variable AC transmission frequencies for offshore wind farm interconnection


A frequency of approximately 10–16.7 Hz has a comparable cost of energy with VSC-HVDC to over 200 km.

Higher than nominal frequency at longer transmission distances incur substantially greater costs with extra cables.

The variation of size and cost with frequency for the offshore platform installations and transformers.


Non-standard AC transmission frequencies have been suggested in literature as a potential competitor to VSC-HVDC transmission for offshore wind farms integration (>100 km). Transmitting at lower than standard 50/60 Hz frequency provides the advantage of longer transmissible range for bulk AC power transfer and potentially lower losses in associated wind farm components. A higher than nominal frequency reduces the size of the required transformers and offshore platforms, potentially reducing cost substantially. This paper examines the selection of non-standard AC transmission frequencies from 1 to 100 Hz presenting a techno-economic analysis and methodology for comparing AC to standard benchmark VSC-HVDC technology in terms of power loss, size/volume of components, CAPEX and operation/maintenance metrics. It is shown at frequencies lower than 20 Hz, cost of energy is comparable to standard VSC-HVDC; due in part to lower number of cables required to carry full load power and the removal of the offshore VSC-HVDC converter station. The key contribution of this work is exploring the potential extended range of transmission capability for non-conventional AC frequency approaches that display comparable power loss and CAPEX/OPEX to VSC-HVDC based transmission for offshore wind integration.


  • Variable AC transmission for offshore wind interconnection;
  • Low frequency AC transmission

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