Study On Impulse Insulation Characteristics Of Transformer Oil Under The Effect Of Electrode And Nanoparticles

Transformer oil is commonly used as liquid insulating medium in power system.Its insulation performance is closely related to the safe operation of power system.A large number of researches on transformer fault show that transformer insulation is one of the most important types of transformer fault,especially with the high voltage grade of power system.The problem of gradual deterioration of transformer insulation characteristics in power system for long-term operation is more prominent.Therefore,improving the insulation characteristics of transformer operation is the necessary way to reduce insulation faults,which has important engineering and theoretical research value.There are many factors affecting transformer oil insulation characteristics,including the nature of transformer oil,the polarity and time of applied voltage,and the distance between electrodes and plates.The electrode mainly affects the breakdown process of liquid dielectric from the aspects of electrode material,electrode surface roughness and electrode geometry.In this paper,the study was based on two factors:electrode plate material and electrode surface roughness.The effects of electrode plate properties on the insulation properties of transformer oil and nano modified transformer oil were investigated.Transformer oil of 25#Kelamayi was chosen as the based fluid.The charge measurement platform and corresponding measurement were built with brass and stainless steel chosen as the electrode materials.The breakdown voltage tests and space charge measurement of Al₂O₃ nano-modified transformer oil were developed to obtain the electric field and space charge distribution of plate gap,conclusions are drawn as follows:The breakdown voltage of transformer oil varies with different electrode materials,among which brass electrode has the highest breakdown voltage,followed by stainless steel electrode.The breakdown voltage is the lowest under the aluminum electrode.This is caused by the distrinct parttens and the amount of charge injected into the liquid dielectric by the electrode plate,in which the brass electrode shows the bipolar charge injection in the transformer oil,while stainless steel shows the unipolar positive charge injection,and aluminum electrode is unipolar negative charge injection.Within a certain concentration range,nanoparticles can effectively increase the breakdown voltage of transformer oil by trapping space charge and hindering the development of streamer,but above the optimal concentration,The breakdown voltage of liquid dielectric decreases due to the agglomeration of nanoparticles.In addition,it is found that the capture ability of nanoparticles to negative charge is much greater than that to positive charge.Considering the characteristics o f nanoparticles and charge injection characteristics of distrinct electrode materials,the breakdown process of transformer oil under distrinct electrode materials has distrinct influence mechanism,therefore,the degree of increase of breakdown voltage is distrinct under distrinct electrode materials.The enhancement effect of nanoparticles on the breakdown voltage under the aluminum electrode plate implanted with single negative charge is the highest.At the same time,we measured the breakdown voltage of nano-modified transformer oil under the combination of aluminum electrode parallel electrode with different surface roughness,and measured and analyzed the electric field and space charge distribution.The following conclusions were drawn:For the aluminum electrode with unipolar negative charge injection pattern,the increase of the surface roughness of the negative plate will increase the amount of charge injected on the electrode surface.The electric field aberration between the plates is increased,and the breakdown voltage is greatly reduced.Therefore,the breakdown voltage of pure transformer oil is the lowest under the combination of electrode plate with rough surface.The nanoparticles can effectively improve the uniformity of electric field of transformer oil under rough electrode plate and thus increase the breakdown voltage.Among them,the breakdown voltage of nano-particles on the surface of the negative plate is the highest under the combination of the plates with rough surface.As the sharpe tip of the surface of the rough plate can effectively adsorb the nanoparticles suspended in transformer oil,when the surface of the negative plate is rough,a large amount of charge injected is trapped by nanoparticles near the plate and trapped around the plate,which inhibits charge injection and effectively improves the degree of electric field aberration between the plates,greatly increasing the breakdown voltage under the plate.However,when the positive electrode is a rough plate,the positive charges absorbed in the double electric layer increase and move to the negative plate under the action of the electric field,leading to the formation of an increase in positive charge injection.Therefore,nanoparticles play an important role in enhancing the breakdown voltage under electrode with rough surface.