Electric field simulation in dc spacers for electrified transportation assets: from voltage transients to steady state

The growing interest in medium voltage dc (MVDC) systems, especially in electrified transportation, opens a cultural and technological gap regarding insulation systems that needs to be filled fast. While, there is a long-term experience in designing ac insulation, only little is known about ageing and diagnostics of MVDC insulation. This paper focuses on the fundamental differences in electric field distribution between ac and dc conditions, as well as during voltage transients and the impact on insulator design. FEA simulations are carried out on a spacer structure to investigate the time dependent electric field intensity during energizing a dc insulator. The temperature dependency of conductivity are also investigated. It is concluded, that the dielectric time constant and temperature can have a strong impact on the field distribution on spacers.