Research On Low Temperature Resistance Of NBR/BR Blended Rubber Used For Seal Of Large-Scale Oil-Emerging Transformer

With the construction of smart grids,transformers are more and more widely used in the industrial field.But once the leakage of oil occurs in large-scale oil-immersed transformers,it will cause energy waste,and will lead to fire,explosion,environmental pollution and other serious consequences which can endanger personal safety.Rubber are generally used to ensure the sealing performance of large-scale oil-immersed transformers.With the excellent performance and affordable price,NBR are widely applied in Oil-immersed transformer seal.But because of poor low temperature resistance,oil leakage often occurs in large-scale oilimmersed transformers in cold areas due to brittle cracking of sealing rubber.Low temperature resistance of NBR can be improved by blending different rubber to modify its property.But all the time,rubber modification is mainly based on experiments,several researcher analyze the microscopic theory.With the development of material science and the improvement of computer performance,combination of two makes molecular dynamics which are applied in many regions become more and more mature.Materials physical and chemical property can be predicted by using molecular dynamics method to get the particle trajectory and the microscopic information during motion.Effect theoretical support can be offered for following macroscopic test by using molecular dynamics method reasonably.In this way,test workload can be reduced and time and energy can be saved.In this paper,it is aimed to use rubber blending modification method to add a small number of BR into NBR which are host materials.In this way,low temperature resistance can be reduced and the condition of embrittlement failure of large oil-immersed transformer seal rubber due to low temperature in cold areas can be reduced.Molecular models of NBR/BR blends with different proportions are constructed and molecular dynamics analysis method is used to research compatibility of NBR/BR blends.It is found that the compatibility of the system is well when the weight ratio of BR is less than 20%.Within the range of good compatibility,it is also found that the glass transition temperature of the system decreases gradually with the increase of BR.The glass transition temperature was 13 K lower than that of pure NBR when 20% BR was added.Mechanical properties of every system under low temperature also be analyzed.It is found that tensile modulus,bulk strain modulus and so on reduce.Increasing of BR reduces rigidity and raises flexibility of system can be concluded.Under low temperature,when 15% BR were added,static mechanical properties is best.Diffusion of oxygen and naphthenic base which is an important component of transformer oil in every blend system in different temperature were also investigated.It is shown that the diffusion coefficient of small molecules increase and diffusion rate become fast when temperature rise.The addition of BR can raise the free volume of system.It is concluded that the molecular diffusion coefficient increases with free volume increase.At the same temperature,the addition of BR can slightly increase the diffusion coefficient of small molecules.When BR exceeds 15%,the diffusion coefficient of transformer oil increase obviously and resistance to oil decrease significantly.In conclusion,when the mass ratio of NBR/BR is 85/15,the low temperature resistance of rubber is better,and the low temperature resistance and oil resistance can be balanced.