Research On The Charge Distribution Characteristics In Oil Paper Insulation Under Impulse Voltage

Electric field characteristics of transformer internal insulation structure under impulse voltage are the key factor of the transformer design.Space charge is one of the important reasons causing electric field distortion in the internal space of oil-paper insulation,its existence and distribution characteristics have significant influence on the properties of oil paper insulation.And the distribution of space charge depends on the process of charge migration,recombination,attachmen t and dissipation.Traditionally,the analysis and calculation of electric field distribution characteristics of insulation structure is based on the equivalent capacitive of field and combines the reasonable safety margin of allowable field strength as a design value.And the distribution of space charge depends on the process of charge migration,recombination,attachment and dissipation.Traditionally,the analysis and calculation of electric field distribution characteristics of insulation structure is based on the equivalent capacitive of field and combines the reasonable safety margin of allowable field strength as a design value.In order to study the distribution space charge,the transport process of the charge should be studied at first.Electric field under impact is very important for the design of the transformer.At present,there are many cases that transformers cause insulation damage when subjected to a lightning strike or occur flashover fault when performing a routine test before delivery.Charge has a significant effect on the electric field distortion,but the current research mainly rely on simulation.The impact voltage of the charge distribution characteristics is not clear,the need to carry out research.In this paper,aiming at the problem of lack of space charge actual measurement,the research of influence factors of space electric field and charge as well as transport process and distribution characteristics of charge are carried out based on Kerr electro-optic effect.The relationship between the distribution of space charge and electric field and electrode metal material,water in oil,temperature is discovered.The dynamic migration of positive and negative charges inside oil-paper insulation system is obtained,and insulation space electric field and charge dynamic and static characteristics with the change of the applied voltage are found.Distribution of space charge and electric field,generation mechanism of charge and migration law of charge in the oil gap space of oil-paper insulation under impulse voltage is revealed.The physical model of oil paper insulation when short oil gap space charge exists under impulse voltage and the calculation method of space charge movement time and space charge density in oil gap are proposed.In this paper,three kinds of metal electrodes for copper,stainless steel and aluminum alloy are studied.Respectively in different metal electrodes with the same external voltage as well as in same metal electrode with different external voltage,compare and analyze charge injection characteristics.Find that metal aluminum injects the maximum amount of charge into the gap of oil,and the copper is the least.It is found that voltage through back calculation is higher than the application voltage at the front of the wave head and the end of the wave tail of the impulse voltage.Reveal the generation mechanism of charge and migration law of charge in the oil gap space of oil-paper insulation under impulse voltage.A charge transport model is established.And the change process of space charge density in the oil gap space along with time under impulse voltage is obtain.Finally,this paper studies the impact of temperature and moisture on the charge injection and transport in the gap of oil-paper insulation system.Find that space charge increases obviously when the water is high.When the temperature is up to 45 Centigrade,the space charge increase obviously.