Thermal ageing effect on the failure time of oil-paper insulation at combined AC-DC voltage

摘要

The oil-paper insulation of converter transformer withstands a long time electrical aging by combined AC-DC voltage and thermal aging during operation. The aging failure mode of converter transformers insulation exhibits a great difference with that of AC transformers. In this paper, a set of accelerated thermal aging experiments at 130 °C were designed, oil-paper specimens were aged for 5, 10, 20 and 35 days, respectively. The unaged oil-paper specimens were also prepared for comparison. The breakdown voltage and failure time of oilpaper specimens of different aging times at AC and combined AC-DC voltage were measured, respectively. The relationship between the failure time and aging time is obtained by using Weibull analysis method. The experiment results show that the breakdown voltage of oil-paper specimens all decrease not much with the increase of thermal aging time. The oil-paper specimens have a longer failure time at combined AC-DC voltage compared with that at AC voltage.