and the generation of molecules with low
weight. If an oxygen molecule is near a
broken end of the polymer chain, a chemical
reaction occurs by bonding the oxygen with
the broken end. This process is called
oxidation and gradually makes the insulation
brittle [13]. Such processes produce both
volatile gaseous products (H
2
O, CO, CO
) as
well as solid low-molecular and Oligomer
components (Methylcyclo-pentadien, to a
lesser extent Methyl-, Vinyl- and
Ethylchloride) which are trapped in the resin.
Since these components are mostly polar, they
exhibit more dielectric losses which can be
observed in the curves of the dielectric
response in the time and frequency domain.
Another process, which contributes to the
degradation of the Epoxy resin and to the
increase of the dielectric losses, is a gradual
weakening of the adhesive strength of the
binding components. Thus the present free
volume within the epoxy resin increases
which allows increased mobility of the polar
groups and components [14]. Therefore an
increase of the dielectric losses in an
insulating system of the high voltage rotating
machine over the years will be an indication
of insulation aging.