Electrical pre-breakdown analysis in dielectric liquid using air bubble deformation in the medium

This thesis presents a study of pre-breakdown phenomena indielectric liquid by investigating the effect of a non-uniform electric fieldon the behavior of an injected air bubble.An air bubble is injected at the tip of the sphere electrode, in asphere-plane configuration, under high D.e. negative polarity voltagesource.The deformed air bubble under different applied voltages and testconditions have been photographed using a sensitive camera ”Zenit 122Hellos 44.2(2/58)” with filters and zoom adjustment.The injected air bubble assumes a prolate spheroidal shape under no,applied voltage and then starts to elongate with the applied voltageassuming a spherical and then elliptical shape.The elongation ratio ( r ) of major to minor semi-axis increase as theapplied voltage increases, and it is found to be extended in the directionparallel to the applied electric field.The ascending r value differ from that of the descending one at thesame voltage level, which show the presence of ”hysteresis” [9], or a loopshape for increasing and decreasing modes.Numerical analysis have been carried out in order to determine theelectrostatic pressure acting on the liquid-air interface and by aid ofphotographic recording to determine the surface tension at the equatorand poles, by using the Krasucki [3] equations the internal pressure havebeen calculated and the relationship with the voltage square have beencleared.The analysis of unstable bubble for eject or compressed against thesphere electrode with sharp edge protrusion, have been cleared and the