The influence of moisture absorption on the electrical breakdown and dielectric behaviour of SRBP

The electrical breakdown and dielectric characteristics of synthetic resin bonded paper (SRBP) are studied as a function of moisture absorption. The breakdown tests, (at 50 Hz) showed a significant (several orders of magnitude) deterioration in the breakdown performance at moisture uptakes greater than 4% of the sample mass. This change in electrical performance was confirmed by dielectric spectroscopy of SRBP samples. The spectra shows an exponential increase in both the permittivity and the dielectric loss as a function of increasing moisture uptake. Dielectric spectroscopy conducted on the paper alone confirms that the changes in the SRBP composite, are dominated by the dielectric characteristics of the paper layers. The spectra of the composite is dominated by an interfacial polarisation effect once moisture is absorbed into the material, and consequently the thin resin layers are subjected to higher electric fields as moisture increases. It is this change in the electrical stress distribution within the composite that leads to deterioration in the electrical breakdown behaviour of SRBP.