Research On The Influence Of Common Impurities On Partial Discharge Of Dry-Type Transformers

Power transformers are an indispensable part of the power system.Among them,dry-type transformers are widely used because of their simple maintenance and no fire hazards.The insulating material of dry-type transformers is solid.When there are impurities in it,the insulation defects caused by impurities will remain at a certain position.Under the long-term operation of the equipment,the discharge phenomenon will first occur here,and it will gradually develop to breakdown.Seriously endanger the safe operation of the equipment.In this thesis,the influence of common impurities on the partial discharge of dry-type transformers is studied from the aspects of simulation and experiment.First,the research significance and development status of the subject are introduced.Second,the mechanism of partial discharge,the type of discharge and the self-decay phenomenon are introduced.The pulse current is selected.The method is used as the basic method for partial discharge detection,and the appropriate filtering system,test loop,correction method,elliptical loop and measures to eliminate test interference are selected.In terms of simulation,two types of impurities,air and metal,are selected.Firstly,a two-dimensional simulation model of the winding is built and simulated to analyze the influence of impurities on the electric field of the winding.It is concluded that the impurities have changed the original uniform electric field structure and that the closer the impurities are to the winding,the more likely to cause partial discharge.Secondly,the physical structure of the dry-type transformer is appropriately simplified,three different three-dimensional transformer models are built and simulated according to the properties of impurities,and the electric field of the dry-type transformer under different conditions is analyzed.Analysis,it is concluded that metal impurities are more harmful than air impurities.In terms of experiments,a dry-type transformer of model SCB13-2000/10 was selected as the experimental sample,and the insulation resistance measurement,voltage ratio measurement,connection label calibration,winding resistance measurement,external withstand voltage,induced withstand voltage and performance parameters were carried out.and other basic experiments.Then a partial discharge detection system was built to conduct partial discharge tests on the experimental samples.By adding two typical impurities to the experimental samples,the experimental phenomena of different impurities in the partial discharge test are studied and summarized.For a dry-type transformer with a large amount of partial discharge,the experimental phenomenon is compared and analyzed with the experimental phenomenon of two typical faults,the fault type is judged,and improvement measures are proposed to ensure that the dry-type transformer can pass the partial discharge test.