Thermal rating implications of the co-location of HV cable circuits in tunnels

Within the past decade, the number of operational cable tunnels in the UK has increased significantly. As the quantity of available tunnel space has increased, the way in which the installations are used is beginning to evolve, notably with regard to the installation of transmission and distribution circuits within the same tunnel environment. This complicates the calculation of the thermal rating, making it difficult to apply standard methods. To address this problem a new rating method has been developed which facilitates a more in depth analysis of the applicable current ratings. This paper presents an analysis of the considerations to be made for both continuous and post-fault rating scenarios, identifying several key trade-offs which allow optimization of the cable asset use.