Experimental Study On Dielectric Surface Flashover Under Nanosecond Pulse In Transformer Oil

Transformer oil is widely used in impulse power equipment for its superiorinsulation performance. But in engineering practice, due to the usage of oil-immersedsolid dielectric as equipment insulation supports, surface flashover across the oil-solidinterface happens easily and becomes the weakness factor of insulation. Plenty ofresearch work has been done on flashover across the oil-solid interface, but subjectedvoltages are focus on DC, AC and LI. Based on the requirement of impulse powertechnology, we carry out some experimental research on the characteristics of severalcommon organic materials.The method to get 50% breakdown voltage value used widely has an obvious errorwhen sample amount is small. To get more credible and available flashover electricfield strength (FEFS), we research on the statistical characteristic of PMMA samples.The result indicates that FEFS obeys Normal distribution and Weibull distribution, andWeibull distribution accords with the physical process better. The way to deal with datafrom small size samples and acquire the eigenvalue of FEFS based on Weibulldistribution is introduced.We study on the influence of dielectric material, flashover distance, surfaceroughness and polarity of voltage on FEFS. The results indicate that: FEFS decreaseswith the fall of relative permittivity of solid material;the flashover voltage increasesbut FEFS decreases with the rise of the flashover distance;the time lag is influenced bythe distance and FEFS decreases with the rise of the time lag, following a negativeexponential function;FEFS increases with the rise of the roughness;FEFS is a littlehigher when a negative polarity impulse voltage is subjected to the curve-shapedelectrode. Further more, the process of flashover in transformer oil is qualitativelydescribed and some tips to be ameliorated in insulation design are proposed.