Passive delay estimation techniques for locating acoustic emission sites in solid dielectric-metal composites

Abstract Many types of power apparatus are constructed by encapsulating metals in epoxy or other dielectric materials. The desired result is a complete impregnation and displacement of all air spaces around the metal. Voids occluded in the insulation will have partial discharge which will lead to the eventual failure of the insulation system near the void. Present quality control methods measure the electrical activity due to partial discharge. If the discharge magnitude is greater than a prescribed limit the apparatus is often scrapped because of the difficulty of determining the cause. Non-destructive techniques have been developed to locate the sites of emissions generated by partial discharge in such dielectric-metal composite structures. Insulating acoustic waveguides are mounted on the surface of the apparatus and are used to receive the acoustic emission signals propagating in the apparatus. A signal processing technique, referred to as generalized cross-correlation, is used to estimate the relative time delay between the received acoustic emissions. These time delays are then used to estimate the locations of the emission sites.