| Partial discharge(PD)is one of the important reasons causing power transformer insulation degradation and breakdown. It is meaningful to detect and diagnose partial discharge in power transformer. Based on microwave and antenna theory, electrical measurement and electromagnetic theory, the ultra-high frequency(UHF)method used in power transformer for PD detection was studied in this paper.A sphere loaded single-pole antenna used in UHF detection of the partial discharge signals in the power transformer has been designed, combination experience and the simulation determined the antenna's parameters. Through changed the cone angle and height of the antenna, the antenna's parameters has been optimized, and the wideband characteristic has been obtained. According to analysis and measurement, the bandwidth of the antenna which VSWR is smaller than 2 is 425MHz to 1.6GHz above, and the absolute bandwidth is bigger than 1GHz.It is high gain in the whole working band, an average of more than 3dB gain, simultaneously, whenθ= 30 0 ~ 900andθ= 270 0 ~ 3300, the antenna has better performance. According to the actual measurement and simulation of the antenna, the bandwidth of the antenna is 430MHz to 1GHz above, the antenna can meet the ultra-high frequency of partial discharge detection needs, and antenna structure is very suitable for installation on transformer.The avalanche effect theory of avalanche triode has been discussed in detail, the simplified model of the triode avalanche process has been inferred out. Through using the circuit simulation software Pspice then analyzing the influence of the storage capacitor and the supply voltage to the pulse waveform, the influence rule has been obtained. The matters needing attention and the choice method of the primary device in the actual manufacture process has been explained. The storage capacitor which is 10p and the 20p pulse circuit has been manufactured, and the output pulse waveform of the electric circuits have been measured actually that pulse width is 980ps and 1180ps and amplitude is 8.9V and 11.6V.The mechanism of the electromagnetic wave which inspired by the Partial discharge of transformer has been researched. The electromagnetic wave in transformer interior each different medium, the different conductor contact surface refraction, the reflection as well as the diffraction situation have been analyzed and calculated. Through the simulation of the PD signals and the laboratory research that established in the transformer physical model indicated: Since the existence of core and windings, the electromagnetic wave had had the diffraction after met core and winding, and caused the energy which the sensor received to have the change. When the original pulse width is certain, UHF signal energy and the square of the amplitude of original pulse is proportional. The original pulse width is the primary factor that affects the UHF signal energy ,and plays the decisive role on the UHF signal energy.According to the PD signal characteristic of the transformer, the metal particles in the oil and corona discharge two typical discharge defects physical model has been designed. In the laboratory, by the use of resistance, sphere loaded antenna sensor and high-speed PD acquisition system, the large number of partial discharge samples which produced by this two kinds of insulation defects have been obtained. Between their cumulative energy of the UHF signal and the discharge relationship has been constructed. Under different conditions, the change rule between them has been studied.
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