Design and Implementation Challenges for Extra High Voltage Gas Insulated Switchgear, Transformers and Subsea Cables at Offshore Platforms

Abstract

Use of GIS to handle bulk power distribution has now become popular in offshore facilities due to the inherent advantage of a compact design. This paper highlights the challenges faced during GIS (and associated items) design based on experience on recent offshore projects and recommendations are proposed for methodical approach. Handling of bulk power at Extra High Voltages poses numerous risks to both personnel as well as assets. This paper discusses the key design parameters, industry standards, interface requirements with transformers/subsea cables/platform structure and installation challenges. Design engineer must be familiar with industry codes so that all design requirements, including proper selection of GIS configuration, are considered from early stages of the project. Omissions or oversight in this regard can impact the whole project. Duration for design, procurement, installation and commissioning phases must be adequately accounted for. Specialist studies such as insulation coordination, very fast transient and touch potentials shall be carried out in addition to usual power system and arc flash studies. Special consideration must be given in case of ring configuration with regard to logic diagrams and differential protection based on multiple CT locations and interconnections. Requirement of voltage selection scheme requires extensive wiring for synchronization function. Relay & CT selection shall be made considering required protection functions, interface with remote location and communication interface with Electrical Control & Monitoring System. Interfaces with transformers and subsea cables shall be in strict compliance with industry standards such as IEC 62271-209 & 211. Requirement of additional surge arrestors shall be verified. GIS exerts large static and dynamic forces on platform steel structure. These are also sensitive to forces during platform lifting and transportation. Support structure suitably shall be designed to mitigate the same. This paper addresses concerns and interface requirements to be considered during design of GIS which will benefit the design engineers, Client personnel and Structural designers along with Project Management Team for safe and smooth execution. Note: Data / details used in this paper are typical for the GIS handled by our Company that may vary based on the makes, models and ratings of GIS.