Valhall

The Valhall HVDC project is a pioneering power transmission system that supplies electricity from the Norwegian mainland to the Valhall oil field in the North Sea. This project is a crucial component of BP's Valhall redevelopment initiative, which aims to extend the field's operational life until 2050.

Project Overview

The Valhall HVDC system consists of a 292-kilometer submarine cable that transmits 78 MW of power from Elkem's 300 kV onshore substation at Lista to the offshore Valhall complex. This power-from-shore solution replaced the previous gas turbine generators on the platform, significantly reducing carbon dioxide emissions by more than 300,000 tonnes and nitrogen oxide emissions by 250 tonnes annually from the field center.

Technical Specifications

The HVDC Light technology, developed by ABB (now Hitachi Energy), is used in this project. The system converts AC power from the onshore substation to DC power at 150 kV for transmission through the subsea cable. At the offshore end, it is converted back to AC at 11 kV to power the entire Valhall field.

The converter stations at both ends of the transmission line use Voltage Source Converter (VSC) technology. The offshore converter is based on a two-level bridge design with a floating capacitor midpoint, switching between 0 kV and -150 kV. This design optimizes the use of the coaxial HVDC cable and minimizes induced ground currents, eliminating the need for cathode protection in the offshore environment.

Benefits and Capabilities

The Valhall HVDC system offers several advantages over conventional power generation methods:

Improved operational efficiency and reduced costsEnhanced control of AC voltage and frequency offshoreAbility to perform direct online starts of large asynchronous machines (up to 15 MW)Resilience against mainland AC system disturbances

The system's performance has been verified through extensive simulations using EMTDC (Electro Magnetic Transient Stability Program), which modeled various faults, disturbances, and large motor starts.

Project Timeline and Implementation

The decision to implement the power-from-shore solution was made in 2005 as part of the Valhall Redevelopment project. The Norwegian government approved the project in 2007, and the system began operation in 2013.

Key Contractors

Several companies played crucial roles in the Valhall HVDC project:

ABB (now Hitachi Energy): Responsible for system engineering, design, and supply of the HVDC Light converter stations

Nexans: Manufactured and installed the 292 km HVDC subsea cable and a separate fiber-optic cable

Fabricom and Wood Group: Awarded the front-end engineering design (FEED) contract

Impact on Valhall Field Operations

The HVDC system powers the entire Valhall complex, which consists of multiple platforms including the new combined Process and Hotel Platform (PH). The PH platform, commissioned in 2013, has an oil production capacity of 120,000 barrels per day and can handle 143 million standard cubic feet of gas per day.

The power-from-shore solution has enabled BP to continue operating the Valhall field efficiently while significantly reducing its environmental footprint. This project demonstrates the feasibility of using HVDC technology for powering offshore oil and gas installations over long distances, setting a precedent for future developments in the industry.