An Investigation of Thermal Ratings for High Voltage Cable Joints through the use of 2D and 3D Finite Element Analysis

Abstract

The operation of power transmission systems requires accurate current ratings for each component within the system. With improvements in computational power, the application of modelling techniques such as Finite Element Analysis (FEA) has become viable for rating calculations. The influence of modelling assumptions implemented in FEA models for directly buried and force-cooled cable circuits has been previously quantified, but without direct consideration of the joint bay. To provide a rating which covers all potential hotspots requires the ability to model the temperature distribution through a joint bay. With the eventual aim of creating 3D FEA models for water cooled joint bays, this paper reports the development of FEA models for rating joints. By extension of modelling techniques developed previously for rating high voltage cables, a steady state 2D axi-symmetric FEA heat transfer model for a 400 kV cable joint has been developed. This allows examination of the sensitivity of the model to variations in the model parameters. Modelling has been subsequently extended and a 3D FEA model of a single joint built, allowing more realistic representations of the boundary conditions experienced by cable joints in service. Knowledge gained from this process informed the development of a 3D model of an un-cooled straight joint bay. Results confirm that such joint bays are not the limiting factor on circuit rating where sufficient core to core spacing has been provided.