Thermal Control Of Ventilation Variable Structure And Shielding Material For Large Air-cooled Turbogenerators

Large turbo-generator is the key equipment of the whole power system,which plays an indispensable role in industrial and agricultural production,national defense,science and technology and daily life.In 2021,thermal power units account for about50% of the installed capacity,providing 66% of the electricity consumption and supporting 75% of the peak load demand.For quite a long time in the future,the large turbo-generator set will still play the role of “ballast rock”.Compared with water-cooled and hydrogen-cooled turbo-generators,large-scale fully air-cooled turbo-generators are widely used in gas-steam combined cycle power plants,phase modulation project of UHVDC transmission station,cogeneration,and waste heat power generation,because of their convenient operation and maintenance,high economic efficiency,and no risk of hydrogen explosion,water leakage and electricity leakage.Air-cooled turbo-generators use air as the cooling medium,of which the cooling capacity is poor.The internal temperature of the generator is high and the temperature difference is large.If the ventilation cooling system of the generator is inefficient or fails,the temperature of its internal heat source components will rise sharply,and in severe cases,the generator insulation,windings and iron core will be burned,resulting in huge economic losses.With the continuous improvement of its single capacity,higher requirements for the electromagnetic load,line load and heat dissipation of the generator are raised.In view of the above scientific problems of large-scale air-cooled turbo-generators,this thesis takes a 150 MW fully air-cooled turbo-generator with a structure of stator omni-radial single-channel ventilation and rotor sub-slot ventilation as the research object.The rotor ventilation variable structure,new stator tooth internal ventilation structure and different shielding materials are proposed in the following aspects,generator rotor ventilation system,stator ventilation system and end shielding materials.The corresponding theoretical calculation methods are proposed,and the electromagnetic-fluid-thermal calculation and research are carried out.First of all,aiming at the serious uneven distribution of air volume in the rotor of large air-cooled turbogenerator,large axial temperature difference and thermal stress of the rotor,this thesis proposes a wind resistance network calculation method with the rotor variable structure for the whole domain ventilation of the generator with the rotor rotation.The variation of ventilation parameters in the whole region and the distribution law of air volume in the rotor are revealed under the variable section of rotor sub-slot and the variable diameter of slot wedge outlet.The rotor flow deviation coefficient angle is proposed to evaluate the ventilation uniformity.The correctness of the proposed method is verified by solving the 3-D fluid local model with the variable structure of the rotor.The air flow state,the size of the vortex in the rotor radial air duct,the wind speed and the incident angle are further studied.Through regression analysis,the analytical formula for vortex in the rotor radial duct is proposed.Secondly,this thesis proposes a nonlinear mapping parameter prediction and optimization method for the rotor ventilation.The fluctuations of the rotor ventilation variable structure parameters on the temperature of the rotor fluid domain and solid domain are studied.The internal fluid heat transfer law is revealed,as well as the relationship between the thermal unbalance coefficient and the flow deviation coefficient.Through the analysis,the input parameters of the variable structure and the output parameters of the rotor flow q and the flow deviation coefficient angle Δθ are determined.Base on the BP neural network and genetic algorithm,the nonlinear mapping parameters are modeled and optimized.The optimized structure of rotor ventilation is determined in combination with practical engineering applications.The flow-heat parameters of the optimized structure are calculated and verified by tests,solving the problems of uneven temperature distribution and high hot spot temperature in the rotor of large air-cooled turbo-generators.Thirdly,in view of the serious heat generation and difficult cooling of the stator winding and core of the air-cooled turbogenerator,a novel internal ventilation structure in the stator tooth is proposed in this thesis.An analytical calculation method of tooth flux density and core loss considering magnetic saturation and tooth shape specificity is proposed.By solving the established 2-D electromagnetic field model of the tooth internal cooling structure,the influence of the structure on the tooth flux density,stator core loss,air gap flux density,radial and tangential electromagnetic force and saturated synchronous reactance is studied.Furthermore,the 3-D fluid-heat transfer model with single-tooth and double-half-slot is established and solved to reveal the distribution of internal air flow and heat dissipation coefficient of air duct wall,the restraining effect of the structure on the potential backflow phenomenon in radial air duct,and temperature control effect on stator heat source component.Finally,in view of the large electromagnetic loss and serious heat generation of the end structural parts of the air-cooled generator,this thesis proposes shielding schemes including all-copper,magnetic-copper composite,and magnetically conductive alloy materials to control the end electromagnetic loss of the generator.The calculation method coupling the generator-grid model considering the control of excitation and rotational speed and 2-D & 3-D electromagnetic field models is proposed.The correctness of the proposed method is verified by excitation current test,end flux density test and leading phase operation test.The loss distribution of each structure at the end with different shielding materials under the rated load and the leading phase operation 0.9 is studied.The distribution characteristics of end loss affected by shielding material characteristics are analyzed.In view of the situation such as the lack of research on the complex air flow state and heat transfer law in the end area of the full air-cooled turbo-generator,the equivalent solution model of the 3-D fluid-heat transfer for the end region is established to study the complex air flow state and heat transfer law.Furthermore,the temperature fluctuation and heat dissipation capacity of each structure at the end with different shielding materials are studied under the rated load and the leading phase operation 0.9.The research findings provide a useful reference for the shielding design and safe and stable operation of the large turbogenerator.