Biaxially oriented polypropylene(BOPP)films

as the core insulating medium of dry DC capacitors used in DC converter valves

are prone to partial discharge under the long-term action of DC voltage

thereby resulting in the deterioration of insulation performance and the decrease of reliability. To study the partial discharge characteristics of BOPP films used in dry DC capacitors under negative polarity DC voltage

three typical defect models of BOPP films were established. The partial discharge characteristics under negative polarity DC voltage were studied by the pulse current method

and four types of characteristic spectrums we

re subsequently extracted through the relationship between the discharge amount and time. The research results indicate that surface discharge defects exhibit obvious “partial discharge cluster” characteristics in the

Q-t

spectrum; corona discharge defects show a generally flat trend; and internal discharge defects display a typical “cascade-like” pattern

with discharge magnitudes concentrated in the low-amplitude range. Under negative polarity DC voltage

the discharge intensity of corona discharge defects triggers a subsequent partial discharge of similar amplitude. For surface discharge defects

the discharge time intervals are concentrated

and a negative correlation exists between the current discharge intensity and the average time interval of subsequent discharges

meaning higher discharge intensities correspond to shorter time intervals.