The Effects of Transient Overvoltages on the Reliability of HVDC Extruded Cables. Part 1: Long Temporary Overvoltages

Extensive simulations have been carried out so far of transient voltages superimposed onto the DC voltage of HVDC cable transmission systems. With the advent of VSC HVDC cable systems, attention has turned to long Temporary Over-voltages in such systems. Preliminary experiments on the possible adverse effects of these long TOVs on the insulation of VSC HVDC cables have started, but no simulation models for estimating their effect on cable life and reliability have been developed yet. This investigation fills this gap by carrying out the simulative evaluation of the life lost by HVDC extruded cables subjected to long TOVs (Part 1) and switching impulses applied during Type Tests (Part 2), so as to compare the severity of these two transient voltages superimposed onto the DC voltage of HVDC extruded cables. This Part 1-paper is focused on estimating the severity of TOVs on extruded cable insulation by: calculating the electric field during the TOV; comparing it with the field during Type Test load cycles; using Miner's law of cumulated damage to calculate the life lost during the TOV, thereby also locating the most severely stressed point of insulation. In Part 2-paper, a similar evaluation for switching impulses and an overall comparison are performed.