Examining the Operational and Environmental Benefits of Using High-Voltage AC Transmission Systems to Supply Onshore Grid Power to Offshore O&G Installations

Abstract

Abstract This paper will discuss the feasibility of transmitting grid-supplied power to offshore platforms at long step-outs using high-voltage AC (HVAC) transmission systems. In recent years, in an effort to reduce their environmental footprint, an increasing number of operators have considered supplying offshore installations with power from mainland electrical grids using high-voltage subsea cables. This is particularly the case in places like The North Sea, where there is a widespread push for O&G producers to ditch on-platform generators in favor of cleaner sources of electricity (hydro, wind, etc). On account of their low electrical losses and high transmission capacity over long distances, subsea DC transmission lines have traditionally been utilized to supply power to offshore platforms — especially for structures at long step-outs from shore (>50 km). However, because these systems require the installation of a DC to AC power converter on the platform (along with other ancillary equipment), they pose significant challenges with regards to space, weight, and cost. This paper will examine how flexible AC transmission systems can be used to eliminate this problem by supplying offshore installations long distances from shore with reliable and eco-friendly grid-supplied power. It will outline the advantages of deploying an AC transmission system over conventional on-platform gas turbine generators – some of which include reduced CO2 and NOx emissions, increased availability, and less maintenance. A case study will be presented on Total's Martin Linge platform in the North Sea, which currently employs the longest subsea AC power link in the world at 163 km (Power Martin Linge, 2015). The AC transmission system helps reduce Martin Linge's CO2 emissions by two million metric tons through elimination of on-platform generators. The paper will focus on the technologies and methodologies that were used on Martin Linge and will discuss the role that power grid simulation and modeling played in lowering the cost for critical power infrastructure, ensuring onshore grid stability, and minimizing overall project risk. The paper will conclude by discussing how producers can use flexible AC transmission systems in other regions of the world to reduce the environmental impact of their offshore installations by capitalizing on clean, reliable grid-supplied power.