PD-Detection vs. Loss Measurements at High Voltages with variable frequencies

Partial discharge-activity (PD) in internal voids in epoxy plastic was measured at AC voltages from below inception to 3 times inception with variable frequencies in the range 0.1 to 100Hz.The results from phase/height analyses were compared to dielec-tric loss measurements and related to the applied voltage and frequency. The character of PD-patterns changed only slightly with voltage and frequency, whereas the apparent charge per cycle was lowest for 50Hz and 100Hz applied voltage. Tand changed with voltage and frequency and the tip-up caused by the inception of internal discharges almost disappeared at low frequencies.The consequences of non-consistent apparent charge and the missing tand tip-up will be discussed with respect to application of low frequency methods on high voltage components.