HTS cable and protection system study for UK's 275 kV transmission network

The global shift towards zero carbon emissions has led to an increased demand for electricity, (e.g., For electrification of heat, transportation, etc.). High-temperature superconductor (HTS) cables offer a high-capacity and small-footprint solution compared to traditional cable technologies, making them ideal for densely populated areas. HTS cables, however, possess different electrical characteristics compared to conventional cables. This paper presents a specific case study of a 12.9 km long 275 kV HTS cable connecting Birkenhead Substation and Lister Drive Substation in the U.K. A dynamic electrical model incorporating the varying resistance of the HTS cable was constructed. The HTS cable model was integrated into an equivalent test network, representing conditions at the target site, to analyse its behaviour and impact on conventional power system protection performance via simulation case studies. The results indicate that differential protection operates reliably, while distance protection is impacted by the varying resistance. However, the proposed HTS cable design at the specified location presents a relatively small change in HTS cable resistance. The impact on distance protection was therefore minimal and can be addressed by considering HTS properties when determining distance protection settings. The study was conducted by considering manufacturer-supplied HTS parameters, network parameters reflective of an actual location in the U.K. grid, and protection requirements specified in the U.K. grid code. The study provides valuable insights into practicality and protection strategies for reliable HTS cable operation in a real-world transmission network. The findings can inform future HTS cable designs and installations globally, as well as provide a framework for further research in this area.