高压直流电场与谐波耦合作用下金属化膜电容器失效研究

The DC-link capacitor is one of the key equipment in voltage source converter based high voltage direct current (VSC-HVDC) system, which still relys on importation nowadays. It is the extreme working condition of HVDC field superimposed harmonics that causes the lifetime of DC-link capacitor is much less than the normal capacitors. Consequently, in the present study, systematic researches are carried out based on the practical operation environment of DC-link capacitor. Results show that the high ratio of harmonics could lead to accelerated capacitance loss at the beginning of the ageing. Furthermore, to investigate the failure mechanism of metalized film capacitor, the aged capacitors are teared down and the extracted metalized films and bi-axial oriented polypropylene (BOPP) films are examined. The observation of metalized film proves that the accelerated capacitance loss is resulted from the electro-chemical corrosion brought by harmonics. The test of base BOPP films indicates that the harmonics result in the degradation of break-down strength, which is originated from the scission of molecules, the decrease of crystallinity, as well as the reduction of activation energy of molecular segment motions. As a result, the accelerated failure of metalized film capacitor under the condition of HVDC field superimposed harmonics could be concluded as the deterioration of breakdown strength of BOPP base film accompanied with the corrosion of metalized film.