Study On Flow Electrification Characteristics Of Oil-paper Insulation Of Converter Transformer In The Wide Temperature Range

At present, UHVDC transmission is a research hotspot in the world, and it is used more and more widely because of its unique advantages. The converter transformer is the core equipment of HVDC transmission and its reliability directly affect the safety of the whole system. The converter transformer withstands not only AC voltage, lightning impulse and operate-over voltage but also DC voltage,superimposed AC-DC voltage and polarity reversal voltage.Under the influence of these voltages, there is great differences for the oil flow electrification between the traditional power transformer and the converter transformer.The experiment research on oil flow electrification was carried out with the typical plane oil-pressboard insulation structure. The oil flow electrification under DC, AC and AC superimposed DC voltage was measured, respectively. The influence of temperature, voltage type,voltage amplitude and oil flow velocity on flow electrification characteristics was investigated. The model of oil flow electrification was established and the expressions of the relationship of streaming current and the above factors were given.Experiment result shows that streaming current increases with flow velocity linearly or exponentially.The temperature has a great effect on oil flow electrification of oil-paper insulation,the streaming current increases with the increase of temperature under AC voltage or without external voltage application.The streaming current increases and then decreases with the increase of temperature under external DC voltage or AC superimposed DC voltage.The amplitude of applied voltage has a great effect on oil flow electrification of oil-paper insulation,the streaming current increases or appears a peak with the increase of amplitude of applied voltage under different experimental condition.The theoretical analysis demonstrates that the increase of velocity enhances the shear stress.The temperature influences the flow electrification characteristics by affecting the conductivity of insulation paper,the conductivity of transformer oil, and the viscosity of transformer oil.The amplitudeof applied voltage influences the flow electrification characteristics of oil-paper insulation by affecting the migration velocity of free ions.