Impact of increasing Underground Cable Penetration in the Swiss Transmission Grid

Switzerland’s AC 220/380 kV transmission network. Driven by growing societal and authoritative demands, these cables introduce challenges such as lowered system resonances causing temporary overvoltages, amplified harmonics affecting power quality, higher reactive power demand, and increased restoration complexity.

An extensive EMT study using detailed network models and CIGRE guidelines confirmed resonance shifts, harmonic amplification, and TOV risks during transient events, prompting

Swissgrid to anticipate mitigation measures including harmonic filtering, reinforcement of operating principles, and supplementary devices. The study also identified significant reactive power compensation needs, highlighting space and cost implications for substations.

In addition, as cable integration further adds complexity to restoration planning, especially for reconstruction cells and black-start operations, entirely new strategies may be required. To safeguard grid reliability, Swissgrid prioritizes meticulous planning, proactive mitigation measures, and ongoing research into alternative technologies to mitigate transient phenomena in future transmission grid architectures.