Experimental Study On UHF Characteristic Of PD Signals In Transformer Oil

Ultra-High-Frequency(UHF) PD detection technique is an effective means for monitoring and evaluation of insulating condition of power transformer.The traditional measuring frequency is mainly between 0.3GHz and 1.5GHz. In order to effectively restrain interference and improve the accuracy of the PD location, measuring and analysis on time-frequency domain characteristics of typical interference and PD signals in the oil is done in our laboratory between 0.5GHz and 5.0GHz in this paper. The results indicate that typical signals from PD models in transformer oil are capable of generating UHF signals up to 3.7 GHz and some interference signals also have a wide band frequency up to 3 GHz. An experimental study on the shielding effect of transformer tank and attenuation characters of interference also is done. It shows that the tank of transformer owns very good shielding effect, which can restrain outer the broad and narrow band interference.Moreover, spectrum characteristic of PD in real-time mode are studied. It is found that Real-time mode is sensitive to inspect the dynamic change of the signal power spectrum. Lastly, by UHF narrow-band measurement simulated in optimum frequency band, Measureing in Narrow-band from 1.2GHz to 1.8GHz can reveal that can effectively restrain interference and improve the accuracy of PD detection.