Abstract

Subsea export power transmission cables for offshore wind farms are being installed more extensively year-on-year due to the increasing demands for power output from renewable sources. With the increasing number of installations, the number of cable failures during installation has increased. One failure mode involves the temporary or permanent radial deformation of armour wires otherwise known as armour wire bird caging which occurs from a combination of twist, bending and compression loads which build up in a cable. This failure mode can lead to significant remediation costs and schedule delays for projects affected.

In this paper, the authors present a method for predicting armour wire bird caging for generic installation configurations based on a review of the root causes from several historical bird caging failure instances. Various numerical models and analyses which simulate the installation conditions are described. The models simulate key response mechanisms including bending-induced twist and inter-layer separation within a cable. Cable loading conditions are compared with cable bird caging limits and the parameters which influence the onset of bird caging are identified. Based on a range of sensitivity analyses, handling curves to assist with installation are developed and a full-scale test validation programme is proposed. This work was performed for a project which received financial and technical support from The Carbon Trust’s Offshore Wind Accelerator (OWA), a collaborative R&D programme funded by nine leading offshore wind developers (EnBW, Equinor, Innogy, Ørsted, RWE, SPR, Shell, SSE, Vattenfall) and the Scottish Government.

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