Analysis On Discharge Characteristics Of The Dielectric Liquids Under Impulse Voltage

Dielectric liquids as insulation dielectric,is commonly used in electric power equipment,its electrical breakdown characteristics is constantly a research focus on electric power industry.Once the dielectric properties of the dielectric liquids is damaged,it will bring hidden danger to electrical equipment,lead huge losses of electric power enterprises.Further study of the discharge mechanism in dielectric liquids has practical significance to improving the electrical equipment insulation strength.The dielectric properties of the insulation can be affected by the internal electric field,and space charge play an important role in changing the distribution of the internal electric field.So the study of internal electric field changing and space charge behavior is particularly important.This dissertation firstly expounds and sums up the basic theory of the dielectric liquids breakdown in detail.Reffering to the particles micro kinetics behavior in the process of liquid breakdown which is described in the field ionization mechanism of dielectric liquids,we established the needle-sphere electrode model and the corresponding mathematical description,then make it dimensionless by π-principle of fluid mechanics.Taking transformer oil as the object of study,through adding the amplitude of 300kV,1.2/50μs standard lightning impulse to needle-sphere model,we work out the interaction relationship among the formation of discharge passage,change of temperature,behavior of charge and strength of electric field during the dieletric liquid breakdown process.We work out and analysis the dielectric liquids discharge process of needle-sphere electrode when the standard lightning impulse voltage value is 400kV,and also compare it with the process when the voltage amplitude is 300kV.The result show that with increasing the applied voltage,the liquid molecules ionize more violently,the dielectric liquids discharges more easily,the field ionization is stronger,the space charge ionized area is larger.The distortion of electrical stress by space charge leads to the stream forming quickly in oil.We do the same work in the transformer oil discharge process when the short pulse is respectively 100ns/2μs and 500ns/2μts,then the results were comparing analysed with it when the condition is standard lighting impulse.Short wavefront pulse voltage takes shorter time to reach the top value,so it can quickly supply the electric field condition which field ionization needs and the electronics around needle electrode having stronger catching probability and forming larger initial ionized area,so compared with the condition of standard lighting electric pulse,its discharge passage to the ball electrode(pole)developments at a higher speed,and its discharge channel radius is larger.