Charges and discharges of conducting particles in a plane oil gap subjected to a dc voltage

Conducting particles in an insulating fluid between horizontal plane parallel electrodes subjected to a dc voltage acquire a charge when in contact with the bottom electrode. Above a well-defined lift-off field, a particle proceeds to bounce up and down. A microdischarge is associated with each particle/electrode contact. Both a theoretical and an experimental investigation has been carried out with single mm-size steel particles (spheres, cylinders) in an insulating oil to appreciate quantitatively the electrical and mechanical interactions of particles with electrodes. Numerical calculations with a charge simulation program of the field-enhancement at the extremities of charged particles approaching or leaving an electrode have been performed. For the first time, the apparent charges transferred by microdischarges have been calculated. Their measurements were found in good agreement with the predicted values. From these results, were obtained estimates of the microgaps at which were produced these discharges and the local breakdown fields