Electric Field Simulation And Optimization Of Large Hydro Generator Stator Bar Ends Based On Electrothermal Coupling

The rated voltage level of large-scale hydro generator is constantly improving,and the single unit capacity is increasing,which puts forward higher requirements for the overall insulation system of the motor.Because the electric field distribution at the end of stator bar is very concentrated,which is the most prone position to produce partial discharge.The insulation problem of stator bar is also one of the main causes of motor damage.How to reduce the electric field intensity at the end of stator bar and prolong the life of motor has become an urgent problem to be solved.In this dissertation,COMSOL Multiphysics finite element simulation software is used to parameterize the modeling of the hydro generator stator bar.The Joule heat generated by the bar conductor is set as the heat source,and the heat transfer module is used for study the simulation object by using the electric thermal coupling physical field.In the selection of corona protection layer material,the epoxy resin / silicon carbide nonlinear composite material is selected.In order to fit the reality better,the lap structure is added in the corona protection layer.By analyzing the parameters of stator bar,the effects of corona protection layer lap length,corona protection layer thickness,main insulation thickness,corona protection layer thermal conductivity,thermal conductivity of main insulation,temperature coefficient,nonlinear coefficient and three section conductivity on the surface electric field distribution and loss density of bar were studied.Finally,genetic algorithm is used to optimize the bar parameters,and the best matching scheme is obtained.The maximum electric field intensity of the optimized scheme is 0.27 k V/mm at three times of rated voltage,which is only 33.3%of the standard 0.81 k V/mm of withstand voltage test,which verifies the reliability of genetic algorithm for bar optimization.When the thickness of the anti-corona layer is in the range of 0.1-0.9mm,the greater the thickness of the anti-corona layer,the smaller the volume loss density and temperature of the bar surface.With the increase of the thickness of the anti-corona layer,the maximum electric field intensity first decreases and then increases.When the thickness of the anti-corona layer is 0.4mm,the minimum value of the maximum electric field intensity is 0.128 k V/mm;the change in the thermal conductivity of the anti-corona layer has little effect on the electric field distribution and volume loss density;the temperature coefficient of the anti-corona layer needs to be compatible with the appropriate The combination of conductivity can make the anti-corona layer achieve the best homogenizing electric field effect;the nonlinear coefficient of the anti-corona layer increases,and the maximum electric field intensity on the surface of the bar shows a decreasing trend.Within a certain range,the larger the nonlinear coefficient,the better.The thickness of the main insulation of the bar is reduced,and the maximum electric field strength and temperature on the surface of the bar are reduced.Therefore,the stator main insulation thinning technology is still the direction of breakthrough in the motor insulation technology.The main insulation is thinned by1 mm,and the slot full rate can be increased by 3%-At the same time,the temperature of the wire rod is reduced by 6℃;the thermal conductivity of the main insulation has a greater influence on the temperature distribution,and the thermal conductivity of the main insulation increases from 0.2W/(m·K)to 0.7W/(m·K).The surface of the wire rod The temperature drops from 79℃ to 56℃,so the research of high thermal conductivity insulating materials has a positive effect on controlling the temperature rise of generators.