Research On Dynamic Deduction Method Of Moisture Content In Inverted Oil-immersed Current Transformer

Current transformer(CT)is the key equipment for power system protection and measurement.In the process of operation,it is easy to cause the main insulation to be damp due to the internal corrosion of oil injection hole retaining ring,which poses a great threat to personal safety and power grid operation.Because the oil sample is taken from the oil valve at the bottom of the CT,it is difficult to fully reflect the change and distribution of the moisture content in different positions of the CT by the internal moisture content detection method.Therefore,this paper studies a dynamic deduction method of internal moisture content of CT in operation state,which is helpful to accurately grasp the insulation state of CT and has important theoretical and practical value.The main work and achievements of this paper are as follows.(1)A three-dimensional simulation model of electric-thermal-fluid multi-physics coupling for 220 k V inverted oil-immersed current transformer(IOCT)is established.The internal temperature field distribution and moisture content distribution of IOCT under normal operation state are obtained by using finite element analysis and multi-physics coupling analysis.The results show that the highest internal temperature appears in the secondary winding.In the oil-paper insulation structure,the closer the area to the secondary winding,the higher the moisture content.(2)By setting damp defects and local overheating defects inside the CT,the distribution law of moisture diffusion in IOCT during damp and local overheating defects is studied,and the influence of environmental temperature,environmental humidity and primary current on moisture diffusion is studied.The results show that at the beginning of damp and local overheating defects,the diffusion rate of moisture in oil-paper insulation is fast,and then gradually slows down.The increase of ambient temperature,humidity and primary current will accelerate the diffusion rate of moisture.(3)By analyzing the influence of environmental temperature and other parameters on the moisture diffusion,the correlation between the internal oil-paper insulation structure of the IOCT and the moisture content of the bottom insulating oil is established.On this basis,a dynamic deduction model of the moisture content in the internal insulation of the IOCT based on the regression decision tree algorithm is established.The moisture content in the oil-paper insulation at different heights from the bottom of the CT can be calculated through the primary current of the CT,the moisture content of the insulating oil in the bottom sampling valve,the environmental temperature and humidity.(4)The experimental platform of LVB-220W3 IOCT is built.The validity of the simulation and dynamic deduction model is verified by installing PT100 thermocouple and moisture content sensor at a specified position.The results show that the calculation results of temperature field and moisture content under normal operation are basically consistent with the experimental results.The temperature deviation is not greater than0.89%,and the maximum deviation of moisture content is 3.49%.The maximum deviation between the calculation results of moisture content and the experimental results under damp defects is 3.41%.