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The risk of breakdown in mineral insulating oil constitutes a critical part in the insulation of high voltage apparatus such as transformer. This paper presents an experimental investigation on transformer oil dynamic breakdown characteristics when subjected to AC voltage. Breakdown tests were carried out on mineral oil samples using a sphere-sphere electrode test cell for various gap lengths 1 mm,...
Two types of resin-coated papers were investigated; kraft papers and heat-resistant kraft papers partially covered with epoxy resin; those were laminated to some thickness. They were thermally degraded at 120degC for 240 to 1320 hours, and their mechanical strength, i.e. tensile strength was measured. The tensile strength of the resin-coated kraft paper decreased with the heating time and became smaller...
This paper discuss the relations between laboratory studies of breakdown precursors in liquids (usually called "streamers"), and practical applications such as high voltage insulation of power transformers and testing of liquids. The conditions existing within high voltage power transformers (ac voltage, moderately divergent electric field, presence of insulating solids, particles in the...
For superconducting high voltage devices liquid nitrogen can not only be used as cooling liquid but also for electrical insulation purposes. Under the programme of a 110 kV fault current limiter project the breakdown and withstand voltages of liquid nitrogen are examined in a new cryogenic high voltage test facility named "Fatelini". Target withstand voltages for this new facility itself...
Many experiments have been undertaken and results published on ageing of high voltage transformer insulation. The objective of these experiments has been to quantify how insulation is affected by moisture and temperature. However, the experiments have invariably been performed on small scale bench top equipment. The validity of scaled up results is always questionable and is exacerbated by the lack...
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...
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