The Study On Fretting Damage Behavior Of Rubber Sealing Material For Large Power Transformer

At present,Chinese advanced manufacturing industry continues to develop rapidly and gradually moves toward industrial modernization.However,as the economic development enters a new normal state,Chinese demand for electricity consumption has increased sharply,which has promoted the development of large-scale power transformers toward large-capacity and high-power trends.With the gradual expansion of the capacity of power transformers,the probability of accidents in the actual operation of power transformers also increases.In recent years,due to the failure of the transformer seal,oil leakage accidents of large-scale transformers occur frequently and faulty unexpected power-off maintenance is increased,resulting in serious economic losses.One of the reasons for the failure of the transformer seal is that the fretting damage of the sealing contact interface is driven by the magnetic excitation of the transformer body.Therefore,the research on the fretting damage behavior of rubber seal materials has certain engineering practical significance and application value.In this paper,a tangential fretting damage test was carried out on the metal material of the transformer box flange and the nitrile rubber sealing material of the transformer,and the surface damage morphology was extracted with the aid of an optical microscope.The fretting damage behavior and regularity of transformer rubber materials under magnetic excitation fretting conditions were studied.The research showed that:(1)The displacement amplitude is the main factor affecting the quality of the contact surface of the transformer nitrile rubber sealing material.As the displacement amplitude gradually increases,the surface damage of the rubber sealing material becomes more serious,and surface pits and fatigue vertical stripes appear;(2)In order to meet the on-site installation conditions of power transformer sealing parts,the rubber material compression rate was used instead of the sealing flange compression force,and the damage behavior and laws of rubber sealing materials under the influence of different rubber material compression rates were studied.As the compression rate of the rubber material gradually increases,the surface damage of the rubber sealing material is more serious.In addition,according to the actual operating conditions of the transformer,the studies have shown that maintaining a moderate compression ratio can achieve a good sealing effect.The compression rate is too small to achieve the sealing effect required by the actual working conditions and causes loose fit,while the larger compression rate will cause material peeling or even faults at the contact interface,thereby speeding up the wear process between the contact surfaces of the transformer sealing material;(3)The effect of the reciprocating operating frequency on the fretting damage behavior of the transformer nitrile rubber sealing material is twofold.On the one hand,when the effect of the reciprocating frequency on the fretting damage of the contact surface is considered separately,the change of the reciprocating frequency does not have a significant impact on the damage morphology;On the other hand,When the displacement amplitude and the compression rate of the rubber material are comprehensively considered,when the above two values increase,as the reciprocating frequency gradually accelerates,the elastic recovery time of the rubber sealing material is shortened,resulting in the cumulative accumulation of elastic deformation of the rubber sealing material and vertical streaks on the contact surface,Pits and material peeling and other undesirable shapes;(4)The number of reciprocating cycles is the main factor affecting the service life of the transformer nitrile rubber sealing material.As the number of reciprocating cycles gradually increases,the surface damage of the rubber sealing material becomes more serious.The gradual increase in the number of reciprocating cycles also directly affects the elastic deformation recovery ability of the rubber sealing material.After a long period of fretting wear with a fast reciprocating frequency,the ability of the rubber sealing material to resist plastic deformation gradually weakens,The ability of the rubber sealing material to resist plastic deformation is gradually weakened.The contact surface has vertical stripes,material peeling and abrasion groove appearance,which seriously affects the quality of the rubber sealing material contact surface.At the same time,this article also uses the finite element method to simulate the micro-moving conditions of the transformer nitrile rubber sealing material.The ABAQUS finite element model of the pair of grinding pairs composed of rubber materials and metal abrasive blocks is established.After the movement,the calculated values of material stress and strain of the contact interface of the rubber material are finally obtained.The force and deformation rules under different influences of the back-to-reset shift amplitude,the rubber material compression rate and the reciprocating operating frequency in the micro-moving condition of the transformer are analyzed.the finite element analysis results show that:with the amplitude and the compression rate of the rubber material gradually increase,the stress and strain values of the rubber material contact interface also gradually increase;When considering the influence of the reciprocating frequency alone,the stress and strain values at the contact interface of the rubber material are similar.On the other hand,when the practice conditions such as displacement amplitude and compression rate of the rubber material are large,as the reciprocating frequency gradually increases,the stress and strain values between the contact interface of the rubber material also gradually increase,and the difference obtained by the finite element simulation.Through the finite element simulation,the change law of stress and strain under different motion conditions can better explain the damage law obtained by the experiment.