Study on the multi-stress aging of stator insulation based on fingerprint parameters

The statistical operators of partial discharge, namely fingerprint parameters, are some important parameters of PD, which can be used to estimate discharge condition of insulation. The statistical operators are produced based on three phase and two intensity distributions by using statistical method, so they are in good connection with the shapes of these distributions and contain most significant information of discharge. Recently they are used widely to estimate the aging condition of insulation system for its advantages. In order to study the aging laws of Epoxy/mica insulation of stator coil, the multi-stress accelerated aging experiment based on the stator bar of 780 kW/6 kV large electric motor has been conducted in the laboratory environment. Partial discharge is tested at the end of each aging cycle, and then several fingerprints of PD parameter distributions are analyzed and studied in this paper. The results of the experiment show that the correlation factor and asymmetry of H_qmax(φ), H_qn (φ) and H_n(φ) at the rated voltage always increase with the aging time. The increase of correlation factor shows that the shapes of phase-resolved distributions of PD parameters become more and more similar between the positive and negative halves of voltage cycle. And the increase of asymmetry operator shows that the discharge in negative half becomes more and more serious with respect to that in positive half. It is concluded that the special fingerprint parameters can be used to evaluate the aging condition of epoxy/mica insulation