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Abstract
This thesis presents a study of pre-breakdown phenomena in
dielectric liquid by investigating the effect of a non-uniform electric field
on the behavior of an injected air bubble.
An air bubble is injected at the tip of the sphere electrode, in a
sphere-plane configuration, under high D.e. negative polarity voltage
source.
The deformed air bubble under different applied voltages and test
conditions have been photographed using a sensitive camera ”Zenit 122
Hellos 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 voltage
assuming a spherical and then elliptical shape.
The elongation ratio ( r ) of major to minor semi-axis increase as the
applied voltage increases, and it is found to be extended in the direction
parallel to the applied electric field.
The ascending r value differ from that of the descending one at the
same voltage level, which show the presence of ”hysteresis” [9], or a loop
shape for increasing and decreasing modes.
Numerical analysis have been carried out in order to determine the
electrostatic pressure acting on the liquid-air interface and by aid of
photographic recording to determine the surface tension at the equator
and poles, by using the Krasucki [3] equations the internal pressure have
been calculated and the relationship with the voltage square have been
cleared.
The analysis of unstable bubble for eject or compressed against the
sphere electrode with sharp edge protrusion, have been cleared and the