| Converter transformer as a vital power equipment in the power system,plays the role of reversing DC into AC and rectifying AC into DC in the process of power transmission and transformation.The valve side bushing of converter needs to bear the combined action of polarity reversal electric field,DC electric field and AC electric field in the actual working environment,which will make the bushing produce a lot of heat,which will greatly affect the insulation performance of valve side bushing.Through the diagnostic test of the insulation aging characteristics of the dry bushing on the valve side of the converter,the potential insulation faults and defects can be easily found.In this paper,the experimental results show that the effect of heat aging on the insulation aging of glass fiber reinforced epoxy resin is studied by means of the effect of alternating current stress.The glass fiber reinforced epoxy resin insulation samples of the side sleeve of the exchange rheological valve were prepared.The electrical aging test platform of the insulation samples under the inclined plate method and needle plate electrode and the partial discharge test platform of the insulation samples after the thermal oxygen aging under the pole plate electrode were built respectively.The tracking,electrical tree and thermal oxygen aging characteristics of the samples were studied.In addition,the micro-morphology of the samples was observed by scanning electron microscope,the functional groups of the samples were measured by Fourier Infrared Spectrometer.The effects of long-term AC stress and thermal stress on the insulation aging process of glass fiber reinforced epoxy resin were revealed.The main research results are as follows:(1)In the process of tracking,pits,micro-cracks,crystalline solids and micro-pores appear on the surface of the composites,the insulation defects collapse,the spherical glass fibers are exposed,the crystalline solids are crushed into filaments and then become powder,the epoxy resin groups are separated,and the powder materials are deposited on the surface of the composites;In the spherical region,the content of C first decreases and then increases,while the content of O and Si first increases and then decreases;The physical and chemical reactions of glass fiber reinforced epoxy resin caused by electric field,thermal field and high energy radiation are the reasons for the morphology changes.(2)The results show that the electrical tree is initiated from the tip of the needle or impurities,and then immediately contacts the interface between the glass fiber and the epoxy resin matrix;In the parallel and vertical glass fiber reinforced epoxy resin materials,the glass fiber attracts the growth of the electrical tree;After contacting the glass fiber,the electrical tree will grow along the glass fiber,and the parallel glass fiber samples show the same behavior.The results show that the growth pattern of the vertical glass fiber is linear and the growth pattern of the vertical glass fiber is agglomerative.(3)The results show that the composites degrade under the action of heat and oxygen,and there are pits,small holes,micro-cracks and cracks on the surface of the composites,and the insulation defects collapse;When the heat and oxygen aging alone,the hydroxyl groups of the composites first undergo oxidation reaction,and then the C-H on the carbon atoms beside the benzene ring.The results show that the bond fracture also occurs;The carboxyl group formed by partial discharge after thermal oxygen aging is more,and new groups are produced,which leads to the fracture degree of molecular chain much greater than that of thermal aging and partial discharge alone;When partial discharge test is carried out on the composite after thermal oxygen aging,thermal oxygen aging will provide convenience for electron injection. |
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