Managing technology step-outs and optimising process performance of starter-helper-generator VFDs on gas-turbine driven LNG trains

The oil and gas industry is considered conservative. However, a few members of the industry came together to design and implement one of the world´s largest, most technologically advanced variable frequency drive (VFD) systems in liquefied natural gas (LNG) processing. Operating in one of the world´s most demanding environments in Ras Laffan, Qatar, the systems show that large electric drives provide significant benefits through process productivity and flexibility [1]. Additionally, this project depended on many of the well-known advantages of VFDs, including motor soft-starting, adjustable process speeds, load flexibility, high availability and regenerative braking. The benefits also include energy efficiency and low impact on the power system, the machine and the environment. This paper discusses a starter-helper-generator application on the world´s largest LNG mega-trains. When the project was conceived there was no standard product available at the required power level that could meet all the project criteria. The project team adopted a process to select the most appropriate VFD technology base, identify where this technology had to be extended (or step-out) and mitigate risk. This equipment has now been in successful operation for more than four years and the paper concludes with a discussion of lessons-learned.