Study On The Infuluence Of Oil Flow On The Development Of Partail Discharge Of Transformer Oil-paper Insulation

At present,most researches on the partial discharge of oil-paper insulation are based on the static or invariant flow velocity,and the influence of the local discharge on the change of oil flow velocity is not studied.With the development of technology,transformer structure is becoming more compact,so the flow velocity must be improved so as to achieve the cooling requirements,and the increase of flow velocity will produce electricity in oil flow,oil flow electrification has become one of the main factors influencing the safe operation of 500 kV power grids.In actual operation,the increase of temperature is often accompanied by the increase of velocity,which has a certain synergistic effect on partial discharge.Therefore,the study of the influence of oil flow on partial discharge,the rule of the influence of velocity on PD development and the synergistic effect of temperature and velocity on discharge are of great theoretical and practical significance.In this paper,firstly,partial discharge tests were carried out on the platform built in laboratory.By analyzing the discharge pattern and phenomenon,the partial discharge process of oil-paper insulation was divided into five stages: beginning stage,slow development stage,stagnation stage,rapid development stage,and prebreakdown stage.In the beginning and slow development stages,the duration of the period is longer and the intensity of discharge was very low,which is mainly the discharge of insulating oil and the surface of insulating paper near the electrode.The duration of the stagnation stage is short,as a transition state,indicating the discharge from the surface of the insulated paper to the interior of insulating paper.The discharge parameters in the rapid development stage increased exponentially,indicating the stage of the discharge entering the destructive type.The breakdown stage indicates that the oil paper insulation is about to undergo a penetrating breakdown.Secondly,by conducting partial discharge tests with different oil flow states,the variation regularity of discharge characteristic parameters at each stage of oil-paper insulation was analyzed,and the influence of abnormal oil temperature and oil flow velocity on the development of oil-paper insulation discharge was explored.The results show that the partial discharge parameters of oil-paper insulation decrease and then increase with the velocity of oil flow,but the discharge parameters at different velocities are increasing with the flow velocity at abnormal temperature.At the beginning of partial discharge,the effect of oil flow velocity is relatively small.With the increase of discharge time,the discharge difference between oil flow velocity become more obvious.The abnormal oil temperature not only increases the discharge parameters,but also increases the discharge parameters between different oil flow velocities.Finally,according to the influence of abnormal oil and oil flow velocity on the partial discharge of oil-paper insulation,the interaction mechanism of influence factors was explained by combining the related theories of oil paper insulation oil flow electrification and partial discharge.Analysis results show that the different oil flow states lead to a large change of oil flow electrification,and the effect of prevent discharge and enhances discharge changed,which made the discharge parameters decrease first and then increase with the flow velocity.The abnormal temperature affects the partial discharge by changing critical flow,streaming current,electrical conductivity and volume resistivity of insulating paper.When the electric field was applied with high electric field,oil flow electrification increases exponentially with the strength of the electric field.It is one of reasons that the influence of temperature and velocity on discharge is more obvious in the later discharge period.