Troll A 3&4

The Troll A 3&4 HVDC project is a significant power-from-shore system implemented on the Troll A platform, the world's largest offshore gas platform operated by Statoil (now Equinor) in the North Sea. Located approximately 70 km west of the Kollsnes onshore gas treatment plant near Bergen, Norway, this project represents the second power-from-shore system delivered to the platform by ABB (now Hitachi Energy).

Project Overview

The Troll A 3&4 project was commissioned in 2015 and provides a total of 100 MW of power to the platform. It consists of two transmissions rated at 50 MW each, complementing the earlier Troll A 1&2 project completed in 2005, which comprised two 44 MW transmissions. Together, these four transmissions form a comprehensive power supply system for the platform.

Technical Specifications

The 2-level VSC technology used in this project operates at a direct voltage of ±60 kV. The system is configured as a symmetrical monopole, which is characteristic of VSC installations. The power is transmitted through subsea cables connecting the onshore station at Kollsnes to the offshore platform.

Key Components

The project includes both onshore and offshore converter stations. At the Kollsnes onshore station, rectifiers connect to the existing 132 kV network through standard power transformers and breakers. HVDC cables then transmit the power to the inverter station on the Troll A platform.

On the platform, the inverter stations are directly connected to very high voltage (VHV) cable-wound motors, eliminating the need for transformers. These VHV motors, rated at 50 MW each on the mechanical shaft, drive the compressor systems. The motors' outgoing shafts are coupled to gearboxes to achieve the required rotational speeds.

Purpose and Benefits

The primary purpose of the Troll A 3&4 system is to power two new compressor drive systems on the platform. These compressors are crucial for maintaining gas production as reservoir pressure decreases over time. By implementing this power-from-shore solution, Statoil has achieved several benefits:

1. Increased gas production capacity2. Reduced carbon emissions by utilizing Norway's predominantly renewable electricity grid3. Improved efficiency and reliability compared to offshore gas turbine generation4. Freed up valuable platform space by eliminating the need for local power generation equipment

Control and Operation

The entire system is governed by the Hitachi's MACH control system, which manages both the power transmission and the VHV motors. This integrated control approach ensures optimal performance and coordination between the onshore power supply and the offshore compressor operations.

Environmental Impact

By utilizing power from shore, the Troll A platform significantly reduces its carbon footprint. This aligns with Norway's commitment to sustainable energy practices, as 96% of the country's electricity comes from renewable sources. The elimination of offshore gas turbine generators also results in more gas being available for sale and reduces local emissions from the platform.

Industry Significance

The Troll A 3&4 project, along with its predecessor Troll A 1&2, represents a pioneering application of HVDC technology in offshore oil and gas operations. It has paved the way for similar projects in the North Sea, demonstrating the viability and benefits of power-from-shore solutions for offshore platforms. This technology has since been applied to other projects such as BP's Valhall and Equinor's Johan Sverdrup, solidifying its position as a key innovation in the offshore energy sector.