Comparison of the AC breakdown voltage of various polymers intended to the conception of a new generation of piercing connectors – influence of geometrical, electrical and climatic factors

The AC breakdown voltage (BDV, 50 Hz) of various polymers is investigated regarding the influence of several constraints: (i) the effect of the electrodes geometry (namely cylindrical, spherical or pyramidally capped point/point) that simulates the interaction between the metallic constituents of the connector (piercing teeth and metallic plates) and those of covered cables (such as the conductor or the presence of voids); (ii) the rate-of-rise of voltage (RRV) and the connection of electrodes to the H.V. source; (iii) the thermal ageing at higher temperatures (namely, 100, 130 and 150 °C) and; (iv) the thermo-hygro ageing under salt rain. The aim of such a study is to identify suitable organic materials that could be intended for the conception of a new generation of piercing connectors that will be used on overhead covered cables. Regarding BDV tests, used polymers cover (i) thermoplastics (namely, polyamide 6, polyamide 66, polyarylamide, polycarbonate, high density polyethylene and polyphenylene sulfide); and (ii) unfilled/fireproofed EPDM rubbers. The obtained results clearly show that breakdown voltage (BDV) with spherical electrodes exhibits the highest values. It is also evidenced that the connection to the H.V. source and the influence of the electrode dimension to the BDV value is significant. Results show that the spherical-pyramidally capped point electrodes exhibit higher BDV than that for the spherical-cylindrical ones for PA 66/50 PC/40, PARA/50 and HDPE. Furthermore, thermal ageing affects seriously BDV of EPDM based materials while polyphenylene sulfide is less damaged due to its highest thermal stability. As concerns thermo-hygro ageing, the moisture absorption is responsible for the significant BDV decrease of polyamide materials (PA 6/50 and PA 66/50).