| Bushing faults is one of the prime reasons causing transformer faults, and the rate trends to increase year by year. This has been one of the problems demanding prompt solutions for safe operation of the power transformers presently. Studies have shown that moisture is a key factor to cause oil-paper insulation degradation, and the failure rate of bushing caused by humidified insulation is in the first place. Correlational researches have verified that moisture is a key factor to give rise to paper oil insulation degradation. There have been numerous conclusions about moisture influence on transformer oil-paper insulation system at home and abroad, but short of related study on condenser bushing oil-paper insulation. Therefore, this paper will study the moisture influence on the correlated characteristics of condenser bushing oil-paper insulation system during the thermal aging process. This will provide the theoretical basis of evaluating aging and humidified conditions, and will be of great importance in engineering application. In this paper, the oil-impregnated paper samples of condenser bushing were accelerated thermally at 130℃ through preparing samples with different initial moisture contents(1%, 3%, 5% and 7%). All the samples were taken periodically for the measurement of thermal aging characteristics and Frequency-domain Dielectric Spectroscopy(FDS) characteristics. After studying the experimental phenomena through qualitative analysis, the comparison with oil-paper insulation transformers is made to lay the theory basis of parameter analysis and the reasons are discussed further. And on this basis the aging rate of oil-paper caused by moisture is analyzed, and the acceleration situation will be evaluated quantitatively. The results are used to establish an equation of oil-paper insulation life loss state of condenser bushing, and it’s verified by correction factor of moisture acceleration situation. The results are shown as follow:① Moisture can accelerate the aging of insulation paper. The fluctuation of moisture content reflects the difference of initial moisture. The ratio of oil-paper insulation system has an obvious effect on the fluctuation of moisture, but barely on the moisture changing rule.② This article qualitatively analyzes the relative permittivity and dielectric loss changing rules. In the 10-3~100 Hz frequency bands, relative permittivity reflects diversity of moisture contents and ageing time. The dielectric loss in 100~102 Hz frequency bands changes regularly with aging time. And the higher initial moisture content, the larger distribution range of dielectric loss curve.③ The decline trend of DP is according with dynamical model. The aging rate of sample with 1% initial moisture content is almost twice faster than transformer oil-paper insulation, but the aging rates of other samples are lower than transformer oil-paper insulation. Under the standard aging rate set, this paper puts forward an acceleration degree equation of moisture.④ The dielectric loss integral value of oil-paper contains aging message and moisture content message. The moisture influence on insulation acceleration equation accords with dielectric loss integral value. Hereby, the loss ratio of lifetime can be calculated. This method solves the problem of acquisition of DP value on the spot in a certain extent. The research results of this paper provide the basis of further analysis about oil-impregnated paper condenser bushing damp evaluation and aging conditions. |
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