Study On Characteristics Of Non-Uniform Thermal Aging Of Oil-Immersed Insulating Paper

Oil-immersed power transformers as part of the core of power transmission equipment, play a decisive role in the power system. Accurate assessment of the decision of its life within the insulation system will effectively protect the safe operation of the entire power system. In the actual operation of oil-immersed power transformers, the temperature gradient between oil and winding results in non-uniform thermal aging of oil-immersed insulating paper, but studies on non-uniform thermal aging of oil-immersed insulating paper are little.Combining laboratory conditions this paper builds test platform for non-uniform thermal aging of oil-immersed insulating paper at first time to study with different temperature levels or different heating environments the aging effect of oil-immersed insulating paper on the variation of the degree of polymerization. At different locations of aging, higher the aging temperature is, faster the degree of polymerization of the paper insulation reduces; for the same temperature level, different heating environments, the temperature gradient and closing the heating sources accelerate the degree of polymerization reducing, but compared to the effect of temperature differences, the influence of heating environments is smaller.The article tested the frequency domain dielectric spectroscopy of oil-immersed insulating paper at different temperature levels and different heating environments, combined with changes in the spectrum shows the effect of temperature and heating environment on paper insulation aging properties. Although insulating papers at different positions are immersed in a certain temperature gradient, their FDS variation curves is determined by the temperature level, higher temperature rating is, greater the real and imaginary parts of the complex dielectric constant are; at the same temperature level, temperature gradient and closing to the heating sources make the real and imaginary parts of the complex dielectric constant largest. This paper introduces the oil-paper insulation dielectric model, the different positions of the insulating oil paper is seen as a whole FDS measurements, the measured values and calculated values of the dielectric model is the same, which illustrates the oil-paper insulating dielectric model effectiveness.In the time domain conditions, using the PDC and RVM at different temperatures and different heating environments analyze dielectric properties of oil-immersed insulating paper, and getting some parameters in the time domain can characterize the thermal environment characteristic quantities. At different locations of oil-immersed insulating paper, PDC and RVM characteristics are determined by the temperature, the polarization and depolarization current values increase as the temperature rises, in RVM curve, the maximum voltage and the initial slope increase as the temperature increases, the time constant of the center make opposite change. For the same temperature rating, different heating objects environments, PDC curves and RVM curves is insignificant, In PDC, thermal conductivity changes characterizes the environment. Temperature gradient and closing to the heating sources immerse conductivity increasing. The time constant of the center in RVM method can characterize thermal aging environment, temperature gradient and closing to the heating sources make the time constant of the center doubled.