Environmental controls on the state of HV cables under the seafloor

Abstract

Submarine high voltage (HV) cables are becoming increasingly important to modern power transmission strategies. There has been a large amount of recent investment in projects such as offshore wind farms and international "megagrid" initiatives, of which submarine HV cables are essential components. A lot of research has been carried out into the thermal behaviour of HV cables buried on land. However, the performance of submarine HV cables has not been investigated extensively, despite several key differences between the two respective environments. The amount of power that can be transmitted along an HV cable is often limited thermally by the maximum operational temperature of the cable components. It is therefore crucial to understand how heat is dissipated from HV cables as comprehensively as possible to ensure reliable, economical, and efficient deployment of these assets.

2D finite element method (FEM) simulations have been developed to examine the impact that certain environmental parameters have on the dissipation of heat generated within submarine HV cables into the surrounding burial sediment. Both conductive and convective heat transfer mechanisms are considered by solving coupled heat and fluid flow equations in a representative geometrical framework. The implications of some realistic inhomogeneous burial scenarios are considered, as is the impact of environmental conditions on cable temperature response times. The FEM model suggests that the most influential environmental factor in determining the nature of the heat flow around submarine HV cables is a quantity called the intrinsic permeability. For sediments with a high permeability, convection can make a significant contribution to the overall transfer of heat from submarine HV cables into the surrounding environment, despite being neglected by traditional techniques for assessing heat flow around cables buried on land. Under these circumstances, cable temperatures are typically lower than for low permeability sediments.

Consideration of the additional cooling effect provided by convective heat transfer in these situations may result an increased cable current carrying capacity, or the potential to reduce the amount of conductor material required for manufacture.

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ORCID for Timothy Henstock: orcid.org/0000-0002-2132-2514

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