Evidence for cavitation in fluorocarbon liquids subjected to alternating electric fields

Abstract

The use of alternating voltages in the study of pre-breakdown processes in fluorocarbon liquids has enabled frequency-dependent effects to be identified with the cavitation process. Acoustic and optical techniques have shown that the events leading to breakdown are intimately connected with stress-induced cavitation in these liquids. The necessary nucleation has been discussed in terms of particle contamination and shock wave propagation in the liquid and suggestions are made concerning the nature of the pre-breakdown light emission.

Optical observation of pre-breakdown and breakdown phenomena in transformer oil

“…The appearance of density changes is always accompanied by shock waves, the generation of which requires a large difference of pressure so that the density change in the liquid is likely to be a gaseous phase generated by the liquid itself. The suggestion agrees with those made by many earlier workers and more recently by McGrath and Nelson (1975) and Nelson and Hashad (1976). The propagation velocity of the shock waves from a negative needle point in transformer oil (1.63 x IO5 cm s-1) is greater than the known sonic velocity (1.112 x lO5cm s-1) and also greater than the shock wave velocity in n-hexane (1.2 x IO5 cm s-1) obtained by Chadband and Wright (1965).…”

High-speed photography of prebreakdown phenomena in dielectric liquids under highly non-uniform field conditions

“…It is reported that light emission is observed when acoustic disturbances generate in a dielectric liquid [25]. Here, the mechanism of ionization of atoms in benzene at the front of the shock wave would be proposed as a likely explanation, i.e.…”