ABSTRACT
A new platform will be built adjacent to theexisting Valhall facilities in the North Sea betweenNorway and Scotland.The new platform as well as all the existingequipment on the Valhall field will be suppliedwith electric power from shore, PFS, through aHVDC Light transmission. This is the first timeHVDC is used to supply an entire offshore acsystem.This paper discuss the background for choosingHVDC Light, the features of the new system andthe present design of the Power From Shore whichis about to proceed into the detailed design phase.
1. INTRODUCTION
The existing Valhall complex consists of fivebridge-linked platforms. In addition, three wellheadplatforms, Hod, Valhall Flank South and North,have been installed about 6 km each, from theValhall complex. The Valhall facilities are subjectto reservoir compaction resulting in seabedsubsidence (about 25 cm per year) and as a resultthe water depth at site has increased by about 5meters. Based on wave consideration and impact onair gap and operation of the original facilities it hasbeen recommended to replace the production andcompression platform and the living quarterplatform with a new facility in 2009.Figure 1. The existing Valhall complex.This new facility will be supplied with electricpower from shore (PFS) through a High VoltageDirect Current (HVDC) Transmission utilizing thelatest development in power electronics andcomputerized control and protection systems. TheHVDC Light transmission system will includeonshore and offshore converter stations joined by a292 km cable. The transmission system will convertac power from Elkem’s 300 kV sub-station at Listato dc power at 150 kV, transmit it through the subseadc cable and convert it back to ac at 11 kV atthe new platform to feed the entire Valhall field.Figure 2 . Single Line Diagram of PFS withHVDC.The system for Valhall will replace offshore gasturbines and deliver up to 78 Megawatt power torun the complete field. This will make Valhall oneof the most environmental friendly fields offNorway´s shores. Following the final installationBP will also achieve a safer and more effectivesource of power supply, resulting in lessmaintenance and a lighter platform solution.HVDC transmissions have been built for more thanhalf a century with a capacity of a single converterup to about 1500 MW at a transmission voltage upto +-600 kV. Applications have normally been bulktransmissions from distant power generation, longunderground or sub-sea cable transmissions orasynchronous ties between different power systems.Applications to feed power to or from offshoreinstallations, using HVDC, have been discussed formany years. However, due to the nature ofconventional HVDC which requires certain strengthof ac system, to operate, this has not been feasiblein the past. Not until the HVDC Light technologywas developed by ABB about ten years ago. Thenew technology is based on transistors as opposedto the conventional HVDC, which use thyristors.


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