Abstract

The design, installation and operation of offshore high power static (seabed) cables are mature technology areas. However, the key missing component in the power transmission system is the water-column portion of the cable that links the floating facility with the static cable on the seabed, the electrical equivalent of a pipeline riser. When such dynamic power cable enabling technology matures it will allow the removal of power generation equipment from platforms, interconnection between offshore installations, utilization of stranded gas for power generation (GTW - Gas to Wire) and its transmission by subsea power networks to the customer, and the transmission to land of power from offshore deep water renewable energy devices.

This paper reviews recent developments in dynamic power cable technology. It discusses the range of configurations and technical requirements required to deliver a fit-for-purpose deep-water product. In particular, mechanical fatigue is addressed together with the need for field specific designs to optimize configurations. Conclusions from the PowerCab JIP recently completed by BPP-Cables are presented. The JIP delivered a prototype 100MW 132kV dynamic AC power cable optimized for extended service life with account taken of the manufacturing and installation issues. The cable has been fatigue tested to verify electrical and mechanical performance in conditions representative of the West of Shetlands.

Introduction

In recent years, there has been a significant increase in the need to transmit subsea electrical power over greater distances at higher power ratings and in ever more challenging environments. A key component of the required technology is the water column power cable, which must be electrically, and mechanically fit-for-purpose throughout the field life. This paper gives an overview of the recent developments in high voltage power cable engineering with respect to dynamic deep-water applications. In addition, the design drivers in relation to the failure modes of subsea power cables and umbilicals are presented. Further, the various associated technology developments are briefly reviewed.

Typically, four modes of operation are involved, as described below:

  • from shore to floating platform

There is a growing need to transmit power from shore to offshore developments. This is primarily to reduce the total CO2 output for a given project in countries such as Norway, where the onshore electricity supply is generated from low-carbon technologies such as hydroelectric, replacing inefficient offshore generators to yield significant CO2 and cost reductions.

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