Experimental Investigation on the Propagation Characteristics of UHF signals in an Actual 110kV Power Transformer

Ultra-high frequency (UHF) detection, due to the advantages such as noiseless measurement, high sensitivity, wide detection range and 3-D localization capability, has been widely applied in power equipment. The propagation characteristics of electromagnetic (EM) waves should be investigated, because it serves as the substantial guides to improve the sensitivity of UHF detection and the efficiency of online monitoring by UHF detection. In this paper, a 110/35/10 kV three-phase oil-filled transformer with complete internal structure was reconstructed to investigate the propagation characteristics of EM waves. The amplitude, frequency band energy and time-frequency property were analyzed. The results show that the amplitude of EM waves decreases nonlinearly and the attenuation rate slows down with the increasing distance between antennas and PD source. During the propagation of EM waves, the higher frequency bands suffer the greater attenuation leading to the less energy ratio and the energy mainly concentrates on the 300 MHz-600 MHz. The time-frequency analysis also proves that higher frequency bands suffer the greater attenuation. These results are considered to be useful for the decisions of the detection sensitivity, sensor positions and the band width of sensors.