Evaluation of fault current limitation techniques in urban meshed 110-kV subtransmission networks

In the municipality of Helsinki, plans to expand its subtransmission network in the next few years predict excessive high short-circuit levels in numerous substations. The existing network embodies overhead lines (OHL) and underground cables (UGC), in many occasions assembled in parallel, as well as combined heat and power (CHP) facilities. Furthermore, it is characterized by meshed topology, which ensures system flexibility and improved reliability; however, this configuration favors propagation of fault currents and voltage sags across the grid. To minimize damage from these, the present study investigates prospective fault current limitation techniques, including the superconducting fault current limiter (SFCL), regarding the features of the Helsinki subtransmission network. This paper inspects the optimal location of these solutions and performs economic assessment. Moreover, it examines the benefits of the employed techniques, assesses whether they achieve the desired operational performance, and quantifies total costs, accrediting load growth for a 40-year period.