Hakim Janah

Evolution of AC breakdown strength of XLPE HV cable after long term test and correlation with physical properties

A dry cured XLPE (cross-linked polyethylene) cable with 15 mm insulation thickness was aged for several years at 135 kV (corresponding to 13 kV/mm maximum stress) on site with load cycles. Electrical tests were carried out on unaged and aged cables. These cables were investigated in their radial direction by cutting thin films on a lathe. Some characteristics of aged insulation such as crystallinity, interfacial diffusion, bow-tie tree distribution, and AC breakdown strength were studied and compared with those of the unaged insulation. Radial breakdown strength obtained from thin films was compared with test results from cables. It was shown that ageing can have a very different influence on electrical characteristics along the radial axis of insulation due to competing factors such as crystallinity, mechanical stresses, and diffusion at semiconductive-shield insulation interfaces.<<ETX>>

Ageing of Polyethylene and Conducting Polymer Blends

The thermal oxidation of pure poly(3-butylthiophene) (P3BT) films has been studied at 80°C in air. Infrared spectroscopy (FTIR) was used for the identification of the key products. The major carbonyl group is ketone in the a-carbon position of the butyl side chain. The thermal oxidation of blended polyethylene(PE) and poly(3-butylthiophene) films at 80°C, in air or nitrogen, has shown that P3BT is preferentially oxidised, according to the same mechanisms.

Method to choose HV cable insulating materials and to characterize their aging

A method to characterize insulating materials is to inject a known quantity of charges into the insulation and to evaluate the electrical potential built up around the zone where charges are injected. If density of injected charges is relevant with respect to charge density which can be sustained by the material, the method is able to point out, notably, the evolution of its dielectric characteristics when submitted to an electrical and/or thermal aging. This paper deals with the comparison of detrapping field of two materials for a given implantation condition. The evolution of this characteristic within the insulation thickness of an HV cable is also characterized.