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Pre-breakdown light emission, current and photo current are measured, simultaneously. For a negative needle point, figures of light emission are divided into two patterns. They change from a bush-type to a tree-type as the applied voltage and the oil surface pressure increases. In the case of the tree-type, they are caused by streamer only at the initial stage. In the case of the bush-type, the lights...
This paper reports the results of experimental investigations on the breakdown phenomenon of transformer oil under inhomogeneous field conditions (rod-plate electrode system) and subjected to DC voltage superimposed on AC voltage. The peak breakdown voltage of transformer oil is found to be decrease with the increasing of ripple content in the applied voltage and gap spacing between electrodes. It...
The electrical pre-breakdown current in dielectric liquids under non-uniform field with tungsten tip have been investigated using photo-optical measuing technique and nanosecond rectangular high voltage pulse generator. The streamer propagation velocity is deduced for each dielectrics from the relation curve of gap spacing vs. breakdown time lag. The dependences of the time lag on gap spacing, voltage...
Pre-breakdown phenomena and the breakdown strength of transformer oil with a model conducting macroparticle have been investigated, Plate electrodes with an area of from 5 to 154 cm2 were used. It has been found that hydrodynamic phenomena play a substantial role in the mechanism of the breakdown of oil. It has been proved that the purity of oil and the electrode area nave no influence on the voltage...
Non-uniform field gaps partially immersed in liquid coolants are essential components in any cryogenic or superconducting apparatus. We have investigated the dc, ac and impulse dielectric breakdown characteristics of non-uniform field gaps partially immersed in liquid nitrogen together with those completely immersed in liquid or cryogenic gaseous nitrogen. It is found that the Sumoto effect appears...
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