Study On The Influence Of Specific Parameters And Physical Properties Of Nanoparticles On Transformer Oil Performance

How to improve the insulation properties of insulating media has always been one of the research hotspots in the field of high-voltage technology.As an important insulating medium in transformers,transformer oil has attracted the attention of a large number of researchers for its dielectric strength and improvement methods.Impurities contained in transformer oil,such as moisture,cellulose,bubbles,etc.,are important factors affecting its insulation performance.Especially moisture,which is an inevitable impurity in transformer oil.Its existence is the main cause of rapid decline of insulation performance,accelerated insulation aging and partial discharge.In recent years,a lot of beneficial results have been obtained by adding nanomaterials to improve the electrical performance of transformer oil,which provides a potential technological approach for further improving the electrical performance of transformer oil.The traditional small bridge breakdown theory believes that purity is the fundamental guarantee for the electrical strength of insulating oil,and the existence of impurities makes its insulation performance greatly reduced.However,the introduction of nanoparticles can improve the insulation strength of transformer oil.This experimental fact shows that the traditional theory of transformer oil breakdown cannot fully explain the phenomenon of high-voltage breakdown of nano-modified oil.Although a large number of nano-modified oil research results have been reported,there are also some important issues that need to be clarified:1)Impurities(Size:10^-7?10^-6 m)and nanoparticles(Size:10^-9 m)in the transformer oil have different effects on the insulation strength of the transformer oil,which indicates that the particle size is a key parameter that affects the performance of the modified oil.It is of great significance to clarify the role of particulate impurities in transformer oil.Existing research lacks clear research on the impact of particle size on transformer oil performance.2)Many researchers at home and abroad have tried to modify transformer oil with many kinds of nanomaterials,and have achieved many positive results.However,there is still a lack of clear and unified understanding on the inherent physical properties of nanomaterials,such as water affinity and high electrical conductivity,have an impact on the characteristics of nano-modified oil.It should be pointed out that water will inevitably be introduced into the production,transportation,storage,injection and use of transformer oil.When the transformer operates in the environment of combined action of thermal,electrical and other factors,the aging of oil paper insulation system will also produce water.Water content is actually the key factor that affects the electrical performance of transformer oil,but many studies on nono-modified transformer oil have not paid attention to this factor,especially the crucial issue of the interaction between water and nanoparticles.Based on this,this paper takes the nano-modified transformer oil as the research object,studies the influence of the specific parameters and physical properties of nanoparticles on the performance of transformer oil,as well as the change law of electrical properties of nano-modified oil under different water content,and puts forward the action mechanism of nanoparticles in nano-modified oil.The related work is as follows:1)The effects of particle size on the insulation properties of transformer oil are obtained by measuring the high voltage breakdown characteristics of the modified oil prepared with different particle size materials.The law of the influence of particle size on the insulation properties of transformer oil is obtained:nanoparticles can improve the insulation strength of transformer oil,and the improvement effect is significant with the decrease of particle size;The large particle size is not conducive to improve the electrical performance of transformer oil,and the micron size particles only play the role of deterioration.The traditional analysis method is used to evaluate the ability of particle size to improve the insulation strength of transformer oil,and it is found that it has certain limitations.By calculating the difference in the proportion of surface atoms of particles of different sizes,the explanation mechanism of the influence of particle size on the insulation strength of transformer oil is proposed:the atomic proportion of the surface of nanoparticles is high,and the surface phase response is mainly observed when they interact with the matrix;The proportion of atoms on the surface of micron sized particles is very small,and it is mainly manifested as a bulk response in the matrix;2)The influence of the factors such as particle dispersion uniformity,particle concentration,particle self-conductivity and surface modifier on the insulation performance of transformer oil is studied.the rules of the above factors on the performance of modified oil are obtained:The ultrasonic dispersion time directly affects the uniformity of particle distribution in the oil.The better the uniformity of the distribution,the higher the insulation strength of the modified oil;For the same material,the use of surface modifiers has a better effect on improving the insulation strength of transformer oil,and its essence is to weaken the agglomeration between nanoparticles and nanoparticles;The improvement of the insulation strength of transformer oil by nanomaterials cannot be a decisive factor in its own electrical behavior.Even Ag nanoparticles with inherent physical properties of high electrical conductivity can increase the insulation strength of transformer oil under certain conditions.It is inferred that the improvement ability of nanomaterials is mainly related to the surface state;The concentration of nanoparticles plays an important role in the density of traps formed in the modified transformer oil,which in turn affects the insulation strength of the transformer oil.3)The electrical properties of water-containing nano-modified transformer oil are studied.and a variety of nanoparticles are used to modify the transformer oil.The breakdown strength and dielectric properties of the system are mainly tested.It is pointed out that there are two kinds of interaction relationships between nanoparticles and nanoparticles,nanoparticles and water in the transformer oil.The former mainly leads to the agglomeration of particles,which not only increases the equivalent size of particles,but also tends to cause the uneven distribution of particle size,which will have a negative impact on the insulation strength of transformer oil;The latter is actually a kind of agglomeration,but this"agglomeration"plays a role in restricting the movement of water and making it difficult to participate in the electric transport process.The interaction of nanoparticles and water is an important reason for the improvement of the insulation strength of transformer oil.The complex permittivity of the system with different water content at high frequency is obtained by using Maxwell-Garnett equation and the calculation method of composite permittivity of three-phase system.The calculated value has a high consistency with the experimental test results.4)Through the analysis of the research conclusions obtained under different experimental conditions in this paper,a more extensive and unified mechanism of nanoparticles in transformer oil is proposed.It is clear that there are two kinds of interaction relations in the modified transformer oil,i.e.nanoparticle-nanoparticle and nanoparticle-impurity,the former has a negative effect on the insulation strength of transformer oil,while the latter has the effect of improving the insulation strength,and there is an optimal range of nanoparticle concentration and impurity content;The nanoparticles are introduced into transformer oil to inhibit the charged particles and impurities in the system.The inhibition capacity is related to the proportion of high active surface atoms,and the particle size determines the surface atom proportion;Whether the modifier is used on the nanoparticle surface or not affects the specific process of impurity inhibition,and the improvement effect on the system performance is consistent.Taking water as an example,the relationship between water content and the concentration of nanoparticles is clearly explained.Taking these basic understandings put forward in this article as the starting point,the research results reported in different literatures can be explained uniformly,which is more general than the explanations given in these literatures,and provides a better way to further reveal the physical mechanism of the electrical properties of transformer oils affected by nanoparticles.