基金项目:
国家自然科学基金(51321063);
南方电网重大科技专项(KJ-2014-170-3);
Project supported by National Natural Science Foundation of China (51321063), Major Science and Technology Project of China Southern Power Grid Company (KJ-2014-170-3);
The ultra-high frequency (UHF) detection is one of the important methods for online monitoring of partial discharges in power transformers. Due to the complex internal structure of power transformers, the propagation characteristics of electromagnetic (EM) waves generated by partial discharges in power transformers are not clear, which limits the application of the UHF method to power transformers. In this paper, based on a 110 kV three-phase three-winding oil-immersed power transformer, an experimental platform of UHF detection was established and the propagation characteristics of UHF signals in the power transformer were investigated. The amplitude, cumulative energy, frequency and propagation time of UHF signals at various measuring positions were analyzed. The results show that the amplitude of UHF signals decreases nonlinearly and the attenuation rate slows down with the increasing propagation distance. The cumulative energy of UHF signals has the similar change rules and wider variation range compared with the amplitude. During the propagation process, the higher the frequency of EM waves is, the more attenuation and the weaker diffraction ability will be, thus the main energy of UHF signals will distributes in the 300~600 MHz. When the detection position is blocked by the windings and iron core, EM waves reach antennas by the diffraction. The first wave of the UHF signals is attenuated seriously, which may affect the location accuracy. The research results in this paper can provide reference and theoretical basis for the selection of UHF antenna frequency band, the installation positions of antennas and the improvement of UHF detection sensitivity.
KEY WORDS :power transformer;partial discharge;UHF;EM waves;propagation characteristics;full-scale experiment;
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