Polarization and Depolarization Current (PDC)
testing is a non-destructive dielectric testing method to determine
the conductivity and moisture content of transformer insulations.
This research was carried out to find the dielectric responsive
function and maximum conductivities of biodegradable and
mineral transformer oils for comparative analysis. Each
insulation oil with different moisture levels (dried, normal, or
wet) was tested. The dried condition was achieved by processing
the oil in a dry-out plant to evacuate the moisture. Normal
condition refers to the oil as taken directly from the drum while
wet condition is the oil after 200ppms of moisture have been
added. The polarization and depolarization current at test DC
voltage of 1000V was recorded for 10,000 seconds. Each test was
repeated five to ten times to collect the most consistent PDC data
and to check the repeatability of each PDC pattern. In the
analysis, the PDC curve was plotted and the DC conductivity of
the oil was calculated. It was found that the trends of the PDC
response for the two transformer oils are different