A Parallel Resonance Investigation in Stockholm's Future Cablified Transmission Grid: A Prospective Study on Transformer Energization

As part of a planned grid expansion in the Stockholm region it is expected that a significant amount of HV cables will be installed. Due to concerns for possible low-order resonances, caused by the large amount of cables, studies have been conducted to investigate the risk of temporary overvoltages following transformer energization in the future power system around Stockholm. It was found that the system has a first parallel resonance point close to 150 Hz which is a possible concern when energizing transformers. However, time domain simulations showed that, despite several worst-case assumptions, the risk of severe overvoltages in the studied cases is small, especially when considering the inclusion of loads.