Some Observations on the Dielectric Breakdown and the Importance of Cavities in Insulating Materials used for Cables and Electrical Machines

摘要

Partial discharges (PD) contribute greatly to the ageing and the breakdown of solid insulating materials. In the present paper, some conductivity measurements are performed relating the conductivity of inner walls of an enclosed cavity to the behaviour of PD in the case of polyethylene and of epoxy resin. The temporary decrease of the PD magnitude is explained in terms of the increase of the cavity inner wall conductivity. The PD behaviour is studied in epoxy resin samples and is explained with the aid of Pedersen's model. Scanning Electron Microscope (SEM) photographs indicate the sort of damage suffered by the cavity walls under electrical stress.