DC Breakdown Strength of Polypropylene Films: Area Dependence and Statistical Analysis

• The dc breakdown strengths of 4-15 μm thick capacitor grade polypropylene (PP) films were determined. The measurements were performed with an automatic measurement system using five electrodes with areas between 0.045 and 9.3 cm2. Some samples werestudied with larger electrodes. Samples were not aged but were measured as received.The measurements were performed in air at room temperature and typically 40-80 breakdowns per sample per electrode area were collected. The Weibull distribution parameters α and β were fitted to the data. Depending on the electrode area and the film grade, the α-parameter values obtained were between 450 and 850 V/μm. The breakdown strength values showed decreasing area dependence with decreasing electrode area and the Weibull scaling law was not valid for the smallest electrodeareas. The α-values for the large sample areas were extrapolated from the small areadata by area and Weibull extrapolation. The area extrapolation overestimated the breakdown strength at 4 m2 by 40-50% whereas the Weibull extrapolation gave anaccuracy of ±15%. The extrapolated breakdown strengths for the full-scale powercapacitors deviated from the capacitor manufacturers test data. This indicated that different defect distributions were responsible for the breakdown strengths in the oil impregnated power capacitors than in the small dry film samples.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

Nyckelord

polypropylene (PP)

biaxially oriented PP (BOPP)

breakdown strength

Weibull distribution

area dependence

extrapolation

capacitor

capacitor film

capacitor dielectric

Chemical engineering

Kemiteknik

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)