Surface tracking along the interphase barrier of a large transformer: effect of moisture within barrier board

Partial Discharge (PD) measurements are an important tool for assessment of the condition of the insulation systems of power equipment such as high voltage transformers. One of the most dangerous failure modes in a large autotransformer is due to surface discharge along the interphase barrier board. Previous work has shown the measurement of Phase Resolved Partial Discharge, PRPD, patterns of surface tracking using either a local PD source only or for a local PD source in the presence of an additional single phase electric field. More recently, results obtained for a barrier board with 9% moisture content in the presence of a two phase applied field as well as a PD source have been reported. In this paper, experiments are described using two phase applied fields for samples with different moisture content of 3% and 6%. The experimental results and discussion highlight the effect of different moisture content within pressboards under the effect of two phase energization, on surface charge behavior. The results should assist in determining the effect of moisture content on PRPD patterns and will help to improve diagnostics of field data captured in real-Time. The experiments have been undertaken at the Tony Davies High Voltage Laboratory, University of Southampton.