This article is the third in a series looking at the development of certain types of ageing phenomena
that could arise in composite insulators in the presence of interfacial defects. The research so far has
concentrated on defects that might appear at the housing-core interface within large hollow core
composite insulators, either as a result of improper handling or through poor manufacturing practice.
In such cases, the cost involved in insulator repla cement would probably be very high. However, in
regard to the physico-chemical processes involved, the considerations presented up to now apply as
well for all types of composite insulators, including those used on overhead lines.