3.3 Corona activity
Another parameter that can cause degradation on the
polymeric insulation is the corona activity. It is analysed by
detecting corona on the testing insulators several times
along the ageing test. The first inspection with the DayCor
II camera was performed after 2500 h of testing. The test
was stopped and when the pollutant layer was dry, the first
inspection was made. No corona was observed on the
surface of any of the four apparatus. Several small regions
of degradation about 6 mm in diameter were observed
visually in sample number 4 (surge arrester without
pollutant layer) along the housing between the sheds, as
shown in Fig. 4a. For this insulation, corona inspection was
carried out again during the clean fog period of the cycle as
shown in Fig. 4b.