Migration of Space Charge in Biaxially Oriented Polypropylene films

Biaxially oriented polypropylene (BOPP) is one kind of the most significant dielectric films for energy storage capacitors. The operating electric field up to 650 kV/mm for the BOPP film can lead to numerous space charge injection, which would be very dangerous to the capacitor. In this investigation, space charge behavior in the BOPP films under various operating temperatures and DC electric fields was studied by the thermal pulse method. At room temperature, the asymmetric bi-polar space charge injection was observed in the BOPP films under DC electric field, and the accumulation of negative charge become dominant gradually with the increase of the experimental temperature. At temperature 70 degrees C, only negative space charge can be observed in the whole bulk, which could mainly be attributed to the mutual shifting of the opposite polarity injected charge with different amounts. As the consequence, the local electric field generated by accumulated space charge can be up to 80% of the applied field.