| ±1100kV converter transformer is the key equipment of UHVDC(ultra high voltage direct current)transmission system,and its reliability directly influence the safe and stable of DC transmission system.As the highest voltage converter transformer in the world,where the insulation oil and paper will bear the high strength and extremely uneven multi physical fields of electricity,magnetism,heat and force,bringing about the difficult to coordinate the multi physical fields.Now,the insulation configuration,structural design and the key process control technology of the ±1100kV converter transformer have not been brokenthrough in china.In order to improve the capability of research and development of UHVDC converter transformer and fight for occupying commanding point in power transmission and equipment.Therefore,focused on the the properties of insulation oil,this paper research the performance of anti-oxidation oil and thermally upgraded paper and finally get the better oil and paper combination according to their aging and electrical characteristics and the influence of aging on the distribution of AC superimposed DC voltage in oil–paper simulated by finite element software.The research results will provide some relevant dates to support for the selection of insulation oil and paper for the manufacture of ±1100kV converter transformer,thus it’s of great engineering value and academic significance to study thermal aging on the properties of the two oil-paper combinations and its distribution of AC/DC electric field.The main conclusions and results are as follows:(1)According to the unique operation condition of ± 1100 kV converter transformer,the Karamay KI-50 X,Shell S4 ZX-I oil and Munksjo upgraded paper are selected then get two oil-paper combinations.According to the thermal aging experiment,the two oil-paper combiations have great anti-aging performace.Besides,the aging rate of KI-50 X oil-impregnated paper is lower than S4 ZX-I oil-impregnated paper.In brief,the anti-aging performance of KI-50 X oil-paper matching is better than S4 ZX-I.(2)The relative dielectric constant,volume resistivity,dissipation and AC,DC,AC/DC voltage breakdown characteristics of oil and oil-paper in different aging state are obtained.The breakdown strength of oil tends to decrease smoothly with the decline of AC component,but the difference between the min and the max breakdown strength is little.The breakdown strength of oil-impregnated paper tends to increase linearly with the decrease of the AC component and its breakdown strength of DC is far greater than AC.In the whole aging period,the electrical performance of SM oil-paper combination is obviously betrer than KM,but both of the two combinations still keep great insulation strength after 90 days aging time.(3)This paper establish the oil-paper insulation model by finite element simulation software,consider the influence of thermal aging on the dielectric permittivity,volume resistivity of insulation oil-paper and get the electric field distribution.The AC voltage distribution is order to capacitive and the electric fields of oil and oil-impregnated paper almost invariant in the whole aging state.While,the DC voltage is resistive distribution and the resistivity ratio of oil and oil-impregnated paper decreases with the aging time goes by,resulting in the electric field in oil increase and the decrease in oil-impregnated paper.Under the AC/DC voltage,the electric field in oil increase with the decrease of AC component.(4)The aging and electrical parameters of the two kinds of oil-paper combinations can meet the requirements of converter transformer.Based on the greart characteristics,this paper consider the anti-aging performance,heat dispersion and optimizing the districbution of AC and DC electric field,that KI-50 X is more suitable for the ±1100kV converter transformer. |
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