In practice the electrical stress plays the main
role in the development of insulation
deterioration and the final breakdown, while
other stresses such as thermal, mechanical,
thermo-mechanical and environmental
stresses are mostly the inception factor for
creation of defects in insulating systems. The
electrical stress can cause partial discharges in
voids and cavities, which erode insulating
materials and may lead to electrical treeing,
which is often referred to as the most
important degradation mechanism in solid
insulations. Therefore the ability of detection
of such deterioration processes is very
important and it is necessary to investigate the
characteristic parameters, which are able to
describe the condition of the insulation.
The measuring results of the depolarization
current, the dissipation factor and the
capacitance as a function of frequency and