Particles in GIS characterization from acoustic signatures

Acoustic techniques are accepted generally for diagnostics of gas-insulated systems (GIS). This paper addresses the problem of risk assessment of moving particles. The main part of the paper gives a general understanding of internal particle movement and excitation of external acoustic signals, leading to signature analysis and simple calculation of characteristics such as mass and length of the particle, and its elevation height in a GIS duct. This is supported by experimental studies of acoustic and electric signals from moving particles. It is shown how partial discharge (PD) at a particle reduces the jumping tendency, and how discharges with time will change when the shape of the particle changes. Experiments on sensor sensitivity and on the coefficient of restitution also have been carried out. The signature analysis and given formulas constitute a good tool for discriminating between harmless and harmful particles, as well as offering a tool for better understanding the particle movement.