PROJECT TITLE :
Effects of gaseous defects on glycerin-impregnated multi-layer film insulation under impulse of 160-nanosecond wave-front
The breakdown behavior of high-purity-glycerin impregnated multi-layer polypropylene (PP) film insulation, with the existence of individually distributed visible little gaseous defects (defects thanks to gaseous inclusions) between the film layers, was investigated experimentally under high voltage impulse of 160-ns wave-front. The experimental results show that, for 100% winding coverage issue, the sample insulation of 10-layer PP film survived when 20 impulses of interval of many minutes at an electrical field of 275 kV/mm. The breakdown field tends to decrease quick and linearly from concerning five hundred kV/mm for one-layer film, which is terribly shut to the intrinsic breakdown field of the PP film, to about 330 kV/mm for four film layers. This tendency of falling of breakdown field becomes gentle and then nearly staying as the amount of film layers (n) increases from four to 10, indicating a flat decay law of n to the (-0.05-th) power. Furthermore, for fiftyp.c-ninetypercent covering factors, the average breakdown field is 254 kV/mm with one-sigma deviation of 51 kV/mm when n ranges from 5 to 8, slightly decaying versus the reduction of covering issue by about tenp.c. Very cheap breakdown field is 173 kV/mm in all cases for regarding thirty samples. The experimental knowledge demonstrate that if visible small gaseous defects don't gather along into a protracted channel between film layers, no flashover can occur along film layer surface at a field of fifteen kV/cm, otherwise flashover is inevitably initiated along the film-glycerin interface.
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