Benefits and drawbacks of selected condition monitoring methods applied to accelerated radiation aged cable

The cable constructed from two ethylene-vinyl acetate copolymer (EVA) based jackets and chemically crosslinked polyethylene (XLPE) insulation was accelerated aged by gamma rays with two dose rates up to 1.4 kGy (6.0 kGy/h) and 1.2 kGy (0.6 kGy/h). Several condition monitoring methods were evaluated and compared: tensile tests, gel fraction and oxidative induction temperature (OITp) measurements, degree of swelling, and isothermal thermogravimetric analysis TGA under air flow. The influence of dose rate, oxygen availability and crosslinking of polymeric constituents on the data obtained were analyzed and discussed. The experiments confirmed that the oxidative degradation extent enhanced the effects measured, particularly those determined by isothermal decay in aerobic conditions. It was found that isothermal thermogravimetry in air is promising potential diagnostic method which could replace currently applicable criteria based on mechanical tests. However, this method is not universal and it is recommended for severely oxidized polymer materials.