Fundamental Characteristics of Electromagnetic Wave Propagation in Non-reflection Coaxial Waveguide (2)

It is necessary to consider the TEM-mode, the higher TE and TM-mode and resonance phenomena in GIS to describe the propagation and detection characteristics for partial discharge measured with the UHF-method. Measurements on the non-reflection coaxial wave-guide simulating GIS were carried out with changing installation and shape of UHF sensor and wave-guide length. This paper describes the output characteristics of UHF sensor above cut-off frequencies, when reflection and resonance phenomena are taken into account. In the frequency region above the cut-off frequencies of the TE11 mode, the output characteristics of UHF sensor shows resonant by reason of the electromagnetic reflection of TE mode at the both ends of wave-guide. At the resonant frequency, the output characteristics of UHF sensor are different by wave-guide length, shape of sensor and sensor installation, distance from end of tank, angle at circumference. The resonant frequencies are function of tank-length and cut-off frequency of tank, and expressed with equation of cylindrical cavity resonator.