Managing cable thermal stress through predictive ratings

The majority of high voltage cables are sized and operated by a continuous current rating which is based on the worst-case assumptions. However, the load on the cables themselves may vary significantly depending upon the time and season. In this paper, a dynamic thermal model for a cable in air installation is built using the finite difference method. The real-time load current and ambient conditions are accessible to allow improved cable modelling. This model is then used to support the rating calculations, the accuracy of which is compared with results obtained from laboratory experiments. A prediction system has been developed to predict the rating from any point forward within the next 24 hours.