The change of the dielectric response in time
domain during the thermo-electrical aging
processes is presented in Figure 7. This figure
confirms the measuring results of the
frequency domain. While the changes of the
measured depolarization current at longer
times (t>100 s) are very low, the change at
short times is significant. That means, that
thermal and electrical stresses cause an
increase of the polarization and depolarization
current, which affects more the fast than the
slow polarization processes.
If the dielectric response function is estimated
with the “Curie- von Schweidler” model at
different aging condition the dielectric
response function constants (A and n) can be
considered as sensitive parameters on the
aging process, as listed in Table 1. These
constants first decrease because of the
reduction of humidity and the post curing
process of the insulation by heating. After that
they increase with the aging time.