Ageing and Moisture Effects on the AC Electrical Strength of Transformerboard

This paper presents an experimental investigation with the aim of examining ageing and moisture effects on the electric breakdown strength of transformerboards under AC voltage conditions. Both virgin and after 29 years of service aged transformerboard samples are tested using a sphere-to-cylinder model electrode arrangement. Our results show that ageing does result in the change of dielectric strength of the tranformerboard, and after 29 years of service, both the AC electric strength and the AC withstand strength (at a loading of 1 minute) of the tranformerboard have reduced by approximately 40% and 25%, respectively. Our results also indicate that when the moisture content in the board is less than 4%, there is no significant change in both the AC electric strength and the AC withstand strength of the transformerboard, with increasing moisture content in the board.