Interpretation of power factor values throughout the life of cast epoxy condenser bushings

The power factor and partial discharge values for cast cycloaliphatic epoxy condenser bushings that have been aged in a humidity chamber at 40°C, 90 percent relative humidity are given. A prediction for the long term saturation value of the power factor and when it will occur in service is given for bushings manufactured with and without silane surfactants. Recommendations are made for acceptable annual increase in power factor for bushings in service. The use of power factor measurement as a field technique for the evaluation of cast cycloaliphatic epoxy condenser bushing integrity is discussed.