抄録
Partial discharge (PD) may take place due to residual defects like metallic particles or microprotrusions inside SF6 gas insulated power apparatus such as GIS, leading to the failure breakdown. Thus, PD measurements are very effective and promising technique to diagnose GIS under operating conditions. However, the signal of PD occurring in SF6 gas is very weak and susceptible to external noises which mainly consist of PD in air. Thus, it is important to distinguish the PD in SF6 gas more sensitively from the external noises.
From the above points of view, we have been investigating characteristics of electromagnetic wave spectrum radiated from PD in SF6 gas and in air using wide-band antennas. In this paper, we propose “phase gate control method” in order to reveal the dependence of the polarity of ac voltage on the electromagnetic wave spectrum. Using the phase gate control method, an attempt is made to separate electromagnetic spectrum caused by PD occurring in SF6 gas from that in air. We also investigate the frequency range where PD spectrum in SF6 gas alone can be detected under noisy conditions. On the basis of these results, we discuss the minimum detectable PD charge in SF6 gas as a function of measuring frequency.
