Detection and characterisation of partial discharges in transformer defect models

Experimental investigation into the behaviour of partial discharges (PD) in different types of defect models are described in this paper. The models were used to study the waveshape and frequency spectra of the signals resulting from discharges. This information is then used to investigate the effect on the signals of the type of discharge. The circuit configuration and data acquisition system are also described. Typical insulation defect models were designed and used to investigate the relationship between PD activity and insulation type. Descriptions of the test results obtained for three types of PDs are described. They include corona, surface discharge along the insulation pressboard in oil and discharge along the outer surface of a bushing. The signals were collected by a wide-band PD measurement system. Analyses of the signals indicate that the type of PD source can be determined using the high frequency components of the spectra. This conclusion is very important in the high-frequency range and importance in the diagnosis process used for PD identification in power transformers.