Abstract:
A solid/liquid insulation interface is considered to be one of the weakest points in a composite
insulation system as it facilitates creeping discharges on the interface when the electric field
strength exceeds a threshold value. This thesis presents an original study on the use of alternative
liquid and solid insulation materials to minimize the effect of damages which occur due
to creeping discharge activity. A point-plane electrode arrangement based test apparatus energized
by a high voltage supply is used for analysing propagation of creeping discharges over
solid/liquid interfaces using visual observation. Firstly, an algorithm is developed to determine
the fractal dimension of creeping discharges propagating over various solid/liquid insulating
interfaces. In particular, it focuses on the variation in creeping discharge patterns with the use
of pure epoxy and Nano-composite epoxy samples. The results show that the pattern propagation
depends on the surface profile and the dielectric constant of the solid material. Next,
the effect of the thickness of solid materials on the propagation characteristics of creeping discharges
is studied and the results show that capacitive mechanism plays a major role on pattern
propagation irrespective of the kind of solid material. Next, the effect of oil level on creeping
discharge propagation over solid/liquid interfaces is studied and the results show that when the
oil level increase, amount of ramification and propagation of streamers decreases. Finally, this
thesis studies the effect of using alternative oils such as copra type coconut oil, virgin type
coconut oil, soya bean oil and sunflower oil on creeping discharge propagation. The results
show that there is an inverse relationship between the amount of tree formation and the dielectric
constant of the liquid. The investigations show that use of nano-composite materials and
alternative oils have a significant effect on creeping discharge propagation over solid/liquid
insulating interfaces.