Featured Case Study

Calculation of Steady-state Thermal Fields around Submerged High Voltage Cables

Submerged high voltage (HV) cables generate heat through resistive heating processes. The thermal fields that develop around submerged HV cables can extend several metres beyond the high temperature conductor domain. If several HV cables are laid in close proximity, or if several HV cables cross past each other, also in close proximity, then the interacting thermal fields can generate local temperatures that might exceed allowable limits. In this project, the temperature fields around two National Grid (NG) cables passing beneath (and perpendicular) to two Scottish Power Energy Network (SPEN) cables, were calculated using COMSOL Multiphysics. The cable layering arrangements (and material assignments) are shown in the figure below.

Figure 1: Cable layering arrangements (and material assignments) for the SPEN and NG cable types

The individual SPEN cables were laid inside air-filled uPVC ducts which were arranged in a touching trefoil configuration, inside a sand-duct domain that was submerged underground (surrounded by soil). The NG cables were laid inside air or bentonite-filled HDPE ducts, either inside a concrete duct surround submerged underground, or submerged underground directly. A cable crossing point of interest is shown in the figure below. The generation of heat inside the conductor domain was accomplished with the use of a volumetric heat source boundary condition (i.e. a cable power density). Some predicted results are also shown.

Figure 2: Top to bottom: CAD image of one of the cable crossing scenarios that were studied, along with some predicted thermal fields, some temperature isotherms and a temperature isosurface

We were able to review the predicted model outcomes directly with our client using a custom-built application for simultaneous and interactive results visualisation. The user interface for the application is shown in Fig.3. For a project like this, with complex, 3-dimensional temperature fields, the application results interface provides our client with an insight that is difficult to achieve with 2-dimensional (static) images in a report.