High Temperature and Electric Field Dependence of Resistivity in Impregnated Polypropylene Film

Biaxially oriented polypropylene film (BOPP) and benzyltoluene are the dominant insulating media in high-voltage capacitors. In order to investigate the electrical performance of impregnated film materials, this paper builds a polypropylene film volume resistivity test platform, which conducts tests for five thicknesses of the film to obtain the change rules of impregnated film in different temperature and field strength. Test result shows that: 1) Volume resistivity decreased after impregnation. At room temperature, the volume resistivity of 13 μm impregnated film decreases from 1.83×10 ¹⁶ Ω m to 1.71×10 ¹⁶ Ω m. 2) Impregnated film is significantly affected by high temperature and electric field. When field strength increases from 10 MV/m to 100 MV/m at room temperature, volume resistivity of the impregnated film decreases from 7% to 17% compared with the dry film. When temperature increases to 353 K and field strength increases to 300 MV/mm, volume resistivity of the impregnated film decreases by more than 30%. 3) The variation of volume resistivity of polypropylene film with temperature and field strength can be described by hopping model. At room temperature, the electron hopping distance increases from 1.3 nm to 1.4 nm, and at 353 K, impregnation makes electron hopping distance increase from 1.8 nm to 2.8 nm. The study of the change rules of the impregnated film at high temperatures and fields can help to establish a more accurate capacitor electro-thermal model.