The dependence of fingerprints relevant to PDs on degradation time and test voltage

Partial Discharge (PD) digital measurement systems allow one to obtain derived quantities (fingerprints) which can be related to the morphology of the discharge site and to its degradation level. Nevertheless fingerprint values can change depending on several parameters characterising the experiments. In this paper, the results of PD tests evidence the dependence of some of the fingerprints, relevant to treeing tests and surface PD tests, on the degradation time and on the applied voltage. As such a dependence is different for different kinds of discharge sites, it is proposed to consider the dependence on degradation time or on the applied voltage as a complementary information useful to perform the diagnostic of insulation systems