Study Of Oil-Paper Insulated Transformers'Aging State Based On PDC Mehtod

As the most important and expensive facility in power transmission and distribution systems, power transformer's operational conditions render tremendous significance for reliability and stability of the power grids. Serious transformer accidents not only cause damage to transformer itself, but also cause the disruption of electricity supply and huge economic loss to society. Presently, in our country many large-scale transformers have run for more than 20 years, the growing problem of insulation aging is a major threat to power grid security risks. Clearly determining their condition their condition would be of tremendous importance to the electricity industry.Some factors like charging voltage, polarization time, depolarization time and humidity have been researched which have some impact on polarization and depolarization current. It is shown that for a homogeneous dielectric material it has a very linear property with increase of the applied voltage. More aging information about the insulation could be got with longer polarization time. When the oil-paper insulation damp, its polarization and depolarization current will significantly increase. Based on the measured PDC aging curve, the Debye model parameters of oil-paper insulation are calculated. Based on Debye model, the resistances and capacitance of the maximum and minimum time constants branch are calculated. The results reveal that, the transformer condition can be obtained from Debye model. In Debye model the parameters Rmax and Cmax are related to aging condition of paper, Rmin and Cmin are related to aging condition of oil.In this paper, the furfural content and infrared spectroscopy have been tested. The results showed that with the deepening of aging , as occurred in the solid insulation paper aging is not reversible, and this aging faster and faster. The insulating oil due to its large size and self-healing nature, have small changes in aging process, and these changes are not obvious.PDC method is not a new theoretical approach; it has been applied in many areas such as cable insulation, the stator insulation. However, its use on transformer oil-paper insulation diagnosis is a new breakthrough. PDC method as a non-destructive measurement of dielectric properties has potential advantages and applications.