Abstract
There is a relative lack of research on the development of creepage discharge in aged oil-paper insulation subjected to AC-DC combined voltage in converter transformers. In this study, based on the physical and chemical properties of oil-paper, we propose a sphere-plate electrode model to study the creepage discharge parameters and characteristic spectra of aged oil-paper subjected to AC-DC combined voltage. The results show that the creepage discharge inception voltage of aged oil-paper is related to the AC voltage component of the AC-DC combined voltage. However, when the DC voltage component is 60 kV, the flashover phenomenon was found to occur in one of the severely aged samples before the AC voltage was applied. Despite being subjected to the same DC voltage, the flashover phenomenon did not occur in three other samples aged to different degrees. Large-amplitude discharges were found to appear earlier in the severely aged samples. At the same creepage discharge stage, as the aging time of the oil-paper increased, the number of large-amplitude discharges was found to rapidly increase, and the time interval between adjacent discharges was found to gradually decrease. At each stage of the creepage discharge, the small-amplitude discharge has a “hump” shaped distribution. The larger the DC voltage component, the shorter the endurance time of aged oil-paper, and the more severe the damage to the oil-paper. The DC voltage component was found to have an accelerating effect on the development of creepage discharge in aged oil-paper insulation.
Highlights
The internal insulation material of the converter transformer, which is one of the major components of the ultra-high voltage direct current (UHVDC) transmission system, is the same as that of the traditional AC transformer
As the operation time of the UHVDC transmission project in China increases, the performance of the OP insulation will gradually deteriorate, and the performance of the insulation system will reduce due to aging
When subjected to AC-DC combined voltage (ADCV), the creepage discharge inception voltage (CDIV) of aged OP is related to the AC voltage component of the ADCV
Summary
The internal insulation material of the converter transformer, which is one of the major components of the ultra-high voltage direct current (UHVDC) transmission system, is the same as that of the traditional AC transformer. The transformer insulating paper aging research team of the international council on large electric systems (CIGRE) indicated in a 2007 report that the average operating life of power transformers in most countries is approximately 30 years [3]. As the operation time of the UHVDC transmission project in China increases, the performance of the OP insulation will gradually deteriorate, and the performance of the insulation system will reduce due to aging. This will gradually increase the probability of accidents in the converter transformer. The failure of converter transformers, which occupy a central role in the
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