On the UHF partial discharge measurement in transformers

Partial discharge detection sensitivity of three types of UHF partial discharge (PD) couplers, reportedly used in the literature, has been studied in comparison using experimentally simulated discharges and those discharges observed during PD acceptance testing of transformers. UHF PD measurements were performed by a digital instrument developed for the purpose. An interesting observation has been that UHF PD inception and detection sensitivity is linked to the appearance of PD pulse current impulses of negative polarity. The occurrence frequencies for PD and common noise sources do not appear to change with the type of the PD coupler used, although individual sensitivities vary. In the last part of the paper typical UHF PD patterns recorded using different couplers during PD acceptance testing of transformer is presented.