The Influence of Space Charges on the Life Exponent from Accelerated Life Tests on PP-based HVDC Cable Insulation. Part 2: Binary Blends and Final Comparison with Ternary Blends

The goal of this investigation is to validate the IPM-Arrhenius electro-thermal life model by means of the results of Accelerated Life Tests performed at different voltages and temperatures on polypropylene blends put forward in the NEWGEN project. Part 1 of this study focused on theoretical arguments and on this validation of such IPM on a ternary blend developed in a first stage. Part 2 (this paper) is devoted to a binary blend developed in a next stage to improve the performance of PP blends from the manufacturing viewpoint. As observed in Part 1 for ternary blends, also the values of life exponent of the IPM found for binary blends in this Part 2 of the investigation are fairly high, thus proving the good voltage endurance of all these PP blends. Again, also for binary blends failure times are scattered and depend strongly on electric field and temperature, as expected. Here, the different behavior of the life exponent of the IPM versus temperature found for blends without and with space charge suppressing additive is explained theoretically and experimentally relying on the influence of space charges. Indeed, space charges lead to an increase of the local field enhancement factor with field and temperature. This raises the life exponent with temperature for the binary and ternary blends without space charge suppressing additive, while the life exponent of the binary blend with space charge suppressing additive decreases with temperature as expected. Thus, the additive performs well also from the viewpoint of the life exponent of the IPM.