More insight into the effects of load cycles and electrothermal stress on HVDC extruded cable reliability in the prequalification test

The long-term prequalification (PQ) test of HVDC extruded cable systems according to CIGRE Technical Brochure (TB) 496 consists of a one year long series of “24 hours” load cycles. The duration of this load cycle test relies on a design life of 40 years at constant rated voltage and on an IPM voltage-time characteristic, without any explicit consideration of thermal and synergistic electro-thermal aging effects related to load cycles. Here, as a sequel of a former investigation, a previously proposed method for estimating failure time percentiles of HVDC extruded cables that accounts for the time-varying temperature during the PQ test load cycles is refined. Moreover, the application of the method is broadened for assessing the sensitivity of a typical HVDC cable design to the electrothermal stress levels within insulation thickness, as well as to the variation of insulation resistivity dependence on temperature and electric field.