More insight into the extension of pre-qualification test for HV and EHV AC extruded cable systems

In a previous paper by the same authors, a new method was proposed for the estimation of time to failure percentiles and life fraction lost in the so-called “Extension of Prequalification (EQ) test” according to CIGRE TBs 303. On these grounds, an alternative to the EQ test was proposed, referred to as “Improved Extension of Qualification (IEQ) test”, thereby taking into account the electrothermal endurance features of a given extruded cable design. Here the new method is investigated in more depth by broadening the previous sensitivity analysis. First of all, temperature transients calculated resorting to a thermal transient model of the cable layers and its surrounding environment are added to the parametric temperature transients previously considered. Moreover, a moderate synergism between the electrical and thermal stress is added to the maximum synergism that was solely treated before: in this way, more sound and accurate indications are derived about the test voltage levels to be chosen in the IEQ test for the various cable designs. Finally, two different designs of HV cables are considered in addition to the two designs of EHV cables previously treated.