Analysis of some measurement issues in bushing power factor tests in the field

The power factor measurement is widely used in the evaluation of bushing insulation conditions in the field. Some measurement issues occur in the field tests which give abnormal readings of bushing C₁ and/or C₂ power factors. This paper provides an engineering analysis of the possible measurement issues in the bushing field tests such as testing a bushing on a transformer or in its shipping crate, or a bushing with wet/contaminated voltage/test tap or wet/dirty porcelain surface.