Acoustic emission from partial discharges in solid dielectrics

Properties of acoustic signals emitted from PD sources in solid dielectrics are less well known in comparison with those in liquids. We have investigated three materials used typically as insulation in high voltage cables and their accessories, namely, polyethylene (PE), silicon rubber (SiR) and ethylene-propylene-diene monomer (EPDM). Several simple geometries of defects were considered, such as spherical voids, cylindrical cavities and fissures. COMSOL Multiphysics software was used to conduct computer modelling of acoustic emission caused by PDs in such defects. A relationship between defect dimensions and frequency of the acoustic signal emitted was established. In spherical voids and cylindrical cavities f ~ 1/d, where d is the void size. In fissures, f ~ 1/(t^0.37w^0.5), where t is the fissure thickness and w is the fissure width.