Propagation properties of PD-induced electromagnetic wave in GIS model tank with T branch structure

The authors investigated the influence of a T-branch on propagation properties of PD-induced electromagnetic (EM) wave measured with ultra high frequency (UHF) sensors in 66 kV and 154 kV gas insulated switchgears (GIS). A low pass filtering (LPF) process for the cutoff frequency of TE11 mode was used to eliminate the higher order mode above TE11 of detected signal. The authors discussed the effects of the T-branch on the positive peak amplitude of the first wave V_p of propagating EM wave after the LPF processing. As a result, TEM mode propagates according to the traveling theory based on the distributed constant circuit with considering the characteristic impedance of the T-branch. In addition, a high pass filtering (HPF) process for the cutoff frequency of TE11 mode was used to eliminate the lower frequency component below TE11 of the detected signal. The authors discussed the effects of the T-branch on the peak to peak amplitude V_pp of propagating EM wave after the HPF processing. The authors compared transmission rate THS of propagating EM wave after HPF processing through T-branch in a straight direction with that T_HR of propagating EM wave after HPF processing turning in a right angle direction at the T-branch. As a result, it was found that T_HS was larger than T_HR with the HPF processing.