Study On The Correlation Between Properties Of Insulation Paper And Paper-making System

Power transformer,as the core equipment of power system,is an essential and important device in the power network.With the continuing increase of power consumption and voltage grade,power transformer is gradually developing towards large capacity,high voltage and technological innovation,but then the frequency of power transformer accidents increases gradually.Among them,accidents caused by breakdown of internal insulation materials accounted for a large proportion.Therefore,as an important insulation material in the power transformer,the strength properties,high temperature resistance and electrical properties of insulation paper need to meet higher requirements.Although various kinds of insulation paper developing rapidly,the plant fiber insulation paper has the advantages of low cost,good electrical properties,high strength properties,easy control of size,wide range of application and environment friendly,etc.It is still an important insulation material in the power transformer.Therefore,plant fiber based insulation paper was prepared from unbleached Kraft pulp.Firstly,the strength properties of plant fiber based insulation paper were studied,including the reinforcing effect of beating and cellulose nano-fibril(CNF)to the insulation paper,and the influence of oil immersion time and temperature on the strength properties of insulation paper was also investigated.The results showed that the suitable beating degree was 50°SR in order to increase the strength of paper sheets,the tensile index can be increased to 84.4N·m·g-1.When CNF was added,the tensile index could be further increased to 95.5N·m·g-1,and the suitable dosage of CNF was 2%(relative to absolute dry pulp)when comprehensive consider insulation paper's strength properties and cost.Through the oil immersion treatment of insulation paper,it was found that the strength properties of insulation paper sheets decreases gradually with the increase of oil immersion time and the oil immersion temperature,the paper without CNF after oil immersion at 150? for 5h,the tensile index decreased to 76.9N·m·g-1,while the tensile index of CNF paper was 80.9N·m·g-1,which showed that the strength properties of the CNF paper after oil immersion was kept at a higher level compared to the samples without CNF.On the other hand,the electrical properties of plant fiber based insulation paper were studied from the system of paper-making.The effects of pulp fiber raw materials,chemical reinforcement and paper-making water on the electrical properties of insulation paper were studied.The results showed that the different raw materials of pulp fiber will affect the electrical properties of insulation paper.The electrical conductivity of water extracts of George Prince Pulp(Canada)was obviously lower than that of Venus Pulp(Chile),and the AC breakdown field strength of the insulation paper in oil was 40.8kV·mm-1,better than that of Venus pulp(Chile)(35.0kV·mm-1).By beating,the alternating current(AC)breakdown field strength in oil increases from 13.1kV·mm-1 to 40.8kV·mm-1,and the relative dielectric constant(sr)and dielectric loss angle tangent(tan?)decreases first and then increases.The suitable beating degree was 50°SR when comprehensive consider insulation paper's electrical properties.Adding CNF can further increase the AC breakdown field strength in oil to 56.4kV·mm-1,and the suitable dosage of CNF was 2%.The influence of paper-making water on insulation paper was investigated.And it was found that with the increase of electrical conductivity of paper-making water,the electrical strength of insulation paper was decreases.The effects of sodium ion in paper-making water on the electrical properties of insulation paper were the biggest compare to the calcium ion,the magnesian ion and the potassium ion.And with the increase of the electrical conductivity of calcium chloride solution,the content of calcium ion,chloride ion and total ion content in the paper was increased.In addition,for sodium chloride solutions with different conductivities,with the increase of conductivity of sodium chloride solution,the content of sodium ion,chloride ion and total ion content in the paper tend to stabilize.