Effective Power Transmission from Offshore Wind Farms

Abstract

To cover future requirements for the offshore wind industry, which demands new innovative technology, a system approach to the transmission / export system has been investigated. Testing, modelling and manufacturing have been carried out to scale cable technology to higher voltage levels. This includes material testing, sample testing, and ultimately the manufacturing of full-scale cable system prototypes. Such prototypes comprise a multitude of different cable accessories, which together have been subjected to rigorous type-and pre-qualification tests per the present industry standards. Subsea HVAC transmission systems are well known, but exhibit different types of transmission losses, especially pronounced for high voltage and longer lengths. Such losses can to some extent be minimized through cable design and a tailored phase compensation system. A recently qualified 145 kV AC system is currently undergoing testing in order to scale this for higher voltages. Subsea HVDC cable systems exhibit far fewer transmission loss types but do require converter stations compromising complex electronics at both ends. Such converters are both costly, large, and add a link length independent loss penalty. A recently qualified 525 kV extruded HVDC system, now capable of operating at higher rated temperature, is a new enabler for large bulk power flow at 1.2 GW per single pole and beyond. Thereby, the technology has been scaled from dry 145 kV cable system to 245 kV AC or, from static 320 kV DC systems to a robust 525 kV DC offshore wind system. Based on successful test results, further prototypes are also to be manufactured in 2023. Floating offshore wind parks currently only exist at lower power levels and voltages. This paper presents how the required high power systems can be enabled using novel technology combined with technology proven for other use.