Accelerated Life Test of Eco-Friendly PP-TPE Insulating Material Using Frequency Acceleration

An accelerated life test was performed under 600 Hz power frequency at 90 °C with an electrode specially designed for a flat specimen to derive the long-term reliability and lifetime index required for power cable development using PP-TPE (Polypropylene-Thermo Plastic Elastomer) insulation materials. It was difficult to ensure failure data for life because failure did not occur well in the accelerated life-test to which the constant-stress test was applied at a low electric field, so it was converted to the step-Stress test and performed. As a result, the lifetime index of PP-TPE was determined to be around 12 to 13 which was comparably lower than that of XLPE (Cross-Linked Polyethylene) having the index of 15. However, the number of failures shows that PP-TPE is smaller than XLPE and is rather more voltage endurance than XLPE, and it is judged that it is difficult to evaluate the characteristics simply with the lifetime index. The cause of initial failure was interpreted as the presence of large TPE lumps in the specimen or low dispersion of TPE. In the future, it is judged that a clearer lifetime index should be derived through long-term ageing experiments on model cables with a thickness of several mm.