PD Signal Propagation Characteristics in GIS and Its Location System by Frequency Components Comparison

Propagation characteristics of partial discharge (PD) signal in gas-insulated switchgear (GIS) were investigated in a laboratory and at a 300 kV underground substation. The laboratory test indicates that signal damping can be attributed to two major mechanisms: reflection due to irregularity of characteristic impedance such as spacers and the mode shift from TEM to TE or TM. Tests at the substation show that the signal damping phenomena are independent of propagation direction and the mode shift gives rise to a large signal damping. The major higher mode seems to be TE11. Amplitudes of observed waveforms using narrow-band filters that agree well with the corresponding frequency components observed with a spectrum analyzer show irregular or random behavior depending upon their observation point. This indicates that narrow-band filters do not seem to be suitable for a PD location system by a frequency component comparison, and the reliability of the system using broadband filters instead is discussed.