Polarization characteristics of metallized polypropylene film capacitors at different temperatures

When the metallized polypropylene film capacitor (MPPFC) is used under high electric field in pulsed power systems, an obvious voltage decay phenomenon will occur. The voltage decay is mainly resulted from the relaxation polarization in dielectric applied under high electric field. This paper focuses on the relaxation polarization in metallized biaxially oriented polypropylene (BOPP) film capacitors. The extended Debye model of relaxation polarization is discussed and the parameters of each RC branch are obtained. Meanwhile, the relationship between the increasing proportion of polarization charge (ΔQa/Qh) and temperature is investigated. The experimental results show that under 1kV, ΔQa/Qh varies from 0.018 to 6.868 with the temperature varing from 10 to 70 /spl deg. Moreover, the equivalent capacitance of capacitors in frequency domain is analyzed with consideration of slow polarization. The analysis shows that both a lower frequency and a higher temperature can accelerate the relaxation polarization and increase the voltage decay. Based on the extended Debye model developed from the polarization charge test, the voltage drop is calculated and the results can match well with those of the voltage maintaining test.