CP TD1 Reference Manual V 1.44
178
About 90% of bushing failures may be attributed to moisture ingress. As already
shown with the winding-to-winding insulation, analysis of bushing insulation is
much more detailed when frequency scans are performed. Figures 12-35 to
12-37 show interesting DF curves of power transformer HV bushings over
frequency.
Figure 12-35 DF of a new 154 kV bushing
Figure 12-36 DF of a RIP 145 kV bushing (MICAFIL new)