Considerations on dielectric design of MVDC gas insulated switchgear

Medium voltage direct current (MVDC) is emerging as a promising enhancement for distribution networks, as well as energy collection for long distance linear renewable source integration. A critical challenge in MVDC systems is the dielectric performance of their components, as field experiences remain limited despite theoretical understanding. MV gas-insulated switchgears (GIS) are at the forefront of this development due to their resilience against humidity and pollution, although the variety of designs and dielectric materials complicates their architecture. The choice of switching concept for interrupting direct current adds further complexity to the dielectric design compared to traditional medium voltage alternating current (MVAC) switchgear. Currently, no standards and nor ratings exist for MVDC switchgear, though technical specifications are being published within the IEC for high voltage direct current (HVDC) applications. This paper presents insights into the design of MVDC SF6-free GIS under project OPHELIA, focusing on two subassemblies with high dielectric stress: bushing and fuse tube. It discusses the measurement of apparent conductivities of insulating materials, considering environmental factors, electrical field simulation in Multiphysics tools like COMSOL. The aim is to raise awareness of MVDC dielectric design specifics and encourage standardization efforts in this area.