Abstract
Loose particles and discharges inside the ducts of a gas-insulated substation (GIS) are considered hazardous to the insulation system. These irregularities or flaws can be detected by using acoustic sensors placed on the enclosure. An elementary review of sound propagation in a GIS together with corresponding experimental results are presented. By using ultrasonic acoustic emission sensors, an excellent sensitivity to discharges and moving particles is obtained. The method offers possibilities for quantification of the flaws, and thereby for a risk analysis. However, the degree of certainty of such an analysis is still low, especially for particles