A deeper insight into impulse levels selection for long DC extruded cable lines

The selection of both lightning and switching impulse test values for a power DC link are mainly based on numerical simulation and past experience on similar links, since well-established and standardized practices are missing. In this paper, as a continuation of a previous investigation, 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 taking into account the impulse withstand behaviour vs. cable length via the enlargement law and the effect of overvoltage attenuation for surges travelling along the cable. In particular, a deeper analysis into the algorithm of voltage impulse level selection is performed aiming at considering the typical range of variation of all the parameters that take part in this process. The analysis is performed via Monte Carlo simulations considering all the variable involved in the estimation of the impulse withstand voltages. This approach is particular useful since at present standardized impulse voltage levels for HVDC cables are still left to an agreement between manufacturer and user.