For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electr...For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.展开更多
The results of the assessment of the influence of paper insulation on the discharge initiation in oil were presented in this paper. This assessment based on the results of performed experimental works and on the analy...The results of the assessment of the influence of paper insulation on the discharge initiation in oil were presented in this paper. This assessment based on the results of performed experimental works and on the analysis of electrical field distribution. Both types of the studies were connected with the model HV （high voltage） electrode setups covered by paper and immersed in oil. Experimental works indicated that the source of ＂weak points＂ of paper-oil model electrode setup is oil, not the surface of metal or insulation wrapping. Such hypothesis, resulting mainly from the measured times to initiations of discharges developing from bare and insulated HV electrodes, was verified by the analysis of electrical field distribution performed on the basis of finite element method applied in the COMSOL Multiphysics software. This analysis confirmed preliminary the made hypothesis. Correlation with the most stressed oil volume law was also observed.展开更多
The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric con...The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric constants between insulation paper and transformer oil,restricted the development of transformer with smaller size and larger capacity.In view of this situation and the transformer’s demand for the dielectric physicochemical and mechanical property of insulation material,polycarbonate,polyester film and polyphenylene sulfide with high high-temperature resistance were chosen for the comparison analysis in this paper We did the 300-day thermal aging experiment on four samples in transformer oil under different aging temperatures of90°C,110°C and 130°C,then analyzed the changes of their dielectric properties.The experiment results are as follows;the permittivity and dielectric dissipation factor of the three polymer materials are apparently smaller than those of the paper both before and after 300-day aging;the volume resistivity and partial discharge inception voltage of the three materials are higher than those of the paper both before and after aging;and the breakdown field strength of polycarbonate is higher than that of the paper both before and after aging,while that of polyester film and polyphenylene sulfide are slightly lower than that of the paper.展开更多
文摘For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.
文摘The results of the assessment of the influence of paper insulation on the discharge initiation in oil were presented in this paper. This assessment based on the results of performed experimental works and on the analysis of electrical field distribution. Both types of the studies were connected with the model HV （high voltage） electrode setups covered by paper and immersed in oil. Experimental works indicated that the source of ＂weak points＂ of paper-oil model electrode setup is oil, not the surface of metal or insulation wrapping. Such hypothesis, resulting mainly from the measured times to initiations of discharges developing from bare and insulated HV electrodes, was verified by the analysis of electrical field distribution performed on the basis of finite element method applied in the COMSOL Multiphysics software. This analysis confirmed preliminary the made hypothesis. Correlation with the most stressed oil volume law was also observed.
基金supported by the National Natural Science Foundation of China(Grant No.50977025)
文摘The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric constants between insulation paper and transformer oil,restricted the development of transformer with smaller size and larger capacity.In view of this situation and the transformer’s demand for the dielectric physicochemical and mechanical property of insulation material,polycarbonate,polyester film and polyphenylene sulfide with high high-temperature resistance were chosen for the comparison analysis in this paper We did the 300-day thermal aging experiment on four samples in transformer oil under different aging temperatures of90°C,110°C and 130°C,then analyzed the changes of their dielectric properties.The experiment results are as follows;the permittivity and dielectric dissipation factor of the three polymer materials are apparently smaller than those of the paper both before and after 300-day aging;the volume resistivity and partial discharge inception voltage of the three materials are higher than those of the paper both before and after aging;and the breakdown field strength of polycarbonate is higher than that of the paper both before and after aging,while that of polyester film and polyphenylene sulfide are slightly lower than that of the paper.
