Kazuo Saitoh

The effect of the polypropylene film on the impulse breakdown strength of the laminated oil-impregnated papers

PPLP (polypropylene laminated paper) used for oil-filled cables in high-voltage transmission systems was studied to determine the effect of the PP film on the impulse breakdown strength. The dielectric breakdown of PPLP was compared with that of Kraft paper alone. It was found that the impulse breakdown strength was affected by the relative position of the PP film and Kraft paper. For this kind of laminated oil-impregnated paper, the most essential factor in the impulse breakdown mechanism is the effect of the electric charges, especially the positive charge, trapped on the surface of the PP film.<<ETX>>

The effects of polypropylene on the impulse breakdown mechanism of the laminated oil-impregnated PPLP

The impulse breakdown mechanism of PPLP (polypropylene laminated paper) is investigated in detail, taking into consideration the effect of PP (polypropylene) film. It is found that, although both positive and negative streamers affect the impulse breakdown mechanism, each effect is very different. That is, the positive charges are trapped on the surface of PP film easily, while the negative charges tend to spread into the insulating material. Consequently, it is suggested that the most essential factor of the impulse breakdown mechanism is the positive charges. Comparison of a sheet of PPLP and a specimen made of Kraft papers and PP film suggests the importance of the effect of oil thin films between Kraft paper and PP film.<<ETX>>

On the AC breakdown mechanism of the laminated oil-impregnated PPLP

The AC breakdown mechanism of oil-impregnated PPLP (polypropylene laminated paper) was investigated. According to the experimental results, AC breakdown strength is not influenced by the insertion place of PP (polypropylene). This situation is considerably different from that of the impulse breakdown mechanism. In the case of applied AC voltage, the authors investigated the effects of Kraft paper and PP on the AC breakdown mechanism of oil-impregnated PPLP, by observing partial discharge current waveforms occurring in the specimens. In this experiment, oil-pressure is 0 kg/mm/sup 2/ at gauge in order to exactly observe discharge current waveforms.<<ETX>>