Oil–water interface dynamics and electrical breakdown in pulsed electric field

Abstract

The motion of immiscible liquids and electrical breakdown at the interface of two horizontal layers of conducting water and transformer oil are studied under vertically oriented nonuniform pulsed electric field. The interface profile is tracked during experiments and shows the appearance and growth of a water cone inside the oil. After the water cone reaches the high voltage electrode located in the oil, three scenarios are observed depending on water conductivity and pulsed voltage amplitude: electrical current flows over the water without plasma formation; plasma onset occurs due to thermal breakdown in the water at the moment the cone tip touches the sphere; plasma onset occurs due to breakdown through a swarm of small water drops atomized from the cone tip under the action of electrical forces. From experiments and numerical simulations, the breakdown time is determined depending on applied voltage amplitude; the oil–water interface behavior in the electric field is analysed; and the electrical force distribution is studied. The experiment and simulation results show good agreement.