Lightning and switching impulse levels selection for long DC cable lines

The impulse test levels play an even more important role for the design of HVDC cables than for HVAC cables. Nevertheless, the selection of both lightning and switching impulse test values for a given power DC intertie are mostly based on numerical simulation and on past experience on similar interties rather than on well-established and standardized practices. In this paper the selection of lightning and switching impulse voltage levels to be applied on short cable lengths in the prequalification and/or type tests is addressed for long DC cable lines (longer than 50 km) taking into account the impulse withstand behaviour with cable length via the enlargement law and the effect of over-voltage attenuation for surges that travel along the cable.