Low frequency high voltage offshore grid for transmission of renewable power

Abstract

AC Power transmission using underground cables at 50 or 60 Hz is limited by the charging current and thus the distance. Often this is the reason to change to the DC technology. However, there is an intermediate solution of low frequency operation allowing longer distances from offshore platform to the onshore station. The railroad frequency of 16.7Hz at the voltage level of 145 kV is fully developed, field proven and in broad commercial use. A higher transmission voltage of 220 kV seems doable. Also 3 core AC submarine cables are commercially available, and can be used without any changes at reduced frequency. This paper presents a preliminary basic design of the low frequency offshore link and discusses the pros and cons in terms of technical feasibility for offshore installations as well as operational aspects.