Abstract:
Ageing is a slow process of degradation of
dielectric properties of cable insulation operating at high
thermal stress. Prolonged thermal stress gradually weakens the
insulation and ultimately leads to failure. Therefore, ageing
studies are important for the design of insulation for high
voltage power apparatus. One of the important properties of
insulation is the resistivity of the material, especially for use in
DC systems. In this paper, the authors have considered volume
resistivity as a parameter to identify the changes with respect to
ageing time. The ageing of insulation, change in volume
resistivity and V-t characteristics are believed to be related. A
batch of fresh LDPE samples was subjected to thermal stress for
different time durations and the volume resistivity and
permittivity of each of the samples had been measured under
different electric fields. The variation in volume resistivity was
analyzed experimentally and theoretically. An attempt has been
made to relate endurance coefficient to changes in resistivity.
Endurance coefficient has been estimated using volume
resistivity.
