| The electric power industry is a critical part of economic infrastructure.With the development of economy,the power industry in China has been developing vigorously,and the scale of China's power grid is also increasing.As the scale of the power grid expands,the demand for the reliability of the power supply is getting higher and higher.The statistical analysis of the actual fault shows that the insulation fault is the main reason that affects the normal operation of the transformer.The properties of oil paper insulation are affected by temperature,moisture,vibration and so on.Water can seriously reduce the electrical strength of oil paper insulation and accelerate the aging of insulation.Therefore,it is very important for preventing transformer accident to detect the moisture content in transformer accurately and effectively and evaluate the harm of water to transformer correctly.However,the water content in the pressboard is difficult to be measured directly.It can only be estimated according to the temperature and the water content in the oil.This paper designs a series of experiments to study the four combinations of two kinds of electric insulating oil and two kinds of insulating pressboards to get the balance curves of water content.The curves are different from the Oommen curves,and the maximum difference between the two curves is 20%.In addition,comparison of four kinds of combination,the water content of KI50X oil immersed pressboard is lower than 25#oil immersed pressboard paper.Therefore,the performance of KI50X oil immersed pressboard is superior.The difference of water content of two kinds of oil immersed pressboard is 16.8%.The type of pressboard has little effect on the water absorbability of the oil immersed pressboardThe temperature of transformer in operation is changing continuously.The water content in the oil-paper insulation varies with the temperature.In this paper,the water transfer characteristics of four kinds of oil and pressboard combinations were studied under the condition of variable temperature.During the heating process,the water is moved from the pressboard to the oil,and the water is migrated from the oil to the pressboard during the cooling process.The rapid change of temperature can seriously threaten the operation of the transformer.Analysis of experimental data shows that water in KI50X oil is more easily migrated during the heating process.The maximum difference of water content changing speed in 25#oil and KI50X oil is 30.45%when the temperature changes quickly,and the maximum difference is 17.3%when the temperature changes slowly.During the cooling process,K150X oil in water is not easy to migrate to the pressboard.The difference of changing speed of water content is 19.41%when the temperature changes quickly,the difference is 4.16%when the temperature changes quickly.The type of pressboard has little effect on the water content changing speed in the oil-paper.The above experiments are carried out without no electric field.But the influence of electric field on the migration of moisture between oil and pressboard needs to be studied because water molecules are polar molecules.The effect of electric field on the steady distribution of water in oil-paper insulation is studied in this paper.In the DC electric field,the water content in the oil drops,the water in the oil moves to the high electric field area,then the high water content area is formed in oil.The formation of the high water content area breaks the original balance,and the water is migrated into the pressboard.Under the DC electric field of 10kV/mm,when the moisture content in the oil and paperboard reaches steady state,the moisture content of the pressboard with the same moisture content is reduced by 19.29%to 33.89%compared with that without electric field. |
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