PD-source identification in solids

It is of great importance not only to detect but also to localize and identify the source of partial discharges (PDs). The intention is to see if there is any potential in identification of defects using an acoustic technique aided by a general theory. The idea is that PDs embedded in a solid material would excite different wave modes, depending on the structure of the defect. Standing waves or cavity resonances of different orders will then result in a different frequency spectra, depending on the geometry of the defect. The authors present some general arguments for the acoustic mode density analysis in flat, hole, or spherical cavities. The investigation demonstrated that the normal resonant acoustic modes of a gas-filled cavity were excited by partial discharges. There was a strong correlation between the frequency spectra experimentally obtained and the resonant modes predicted by the theory. It is concluded that the frequency spectra from acoustic detection of PDs can give information on the form of cavity in which it occurred