On Transient Electrical Cable Stresses in Next Generation Multiterminal HVDC Systems

This paper examines transient cable voltage stresses in multiterminal (MT) HVDC systems, with a particular focus on DC circuit breaker integration. The bipolar HVDC configuration with dedicated metallic return (DMR) and modular multilevel converter (MMC) technology is considered. The scope of this paper is driven by recent grid planning initiatives of German transmission system operators (TSOs). To provide a first indication of cable overvoltages in next generation MT systems, a detailed parametric study is conducted by means of electromagnetic transient (EMT) simulations. It is observed that the integration of DC circuit breakers can significantly reduce maximum cable overvoltages compared to MT systems without DC circuit breakers. For the MT system considered, the peak voltage levels are in a comparable range to those for point-to-point schemes in bipolar configuration. Although the integration of DC circuit breakers does not result in higher peak values, novel voltage waveshapes are observed for certain fault events. The obtained overvoltages provide an indication of potential cable stresses in future multiterminal systems and represent a profound basis for more targeted discussions with cable manufacturers.