| Under normal operating conditions,the generator is in three phase symmetrical state,but there are a lot of unbalanced loads in power system composed of generators,transmission line,power transformation and distribution devices and a large number of user equipment,that could cause asymmetric operation of the generator.There will be negative sequence current in stator winding of high speed turbine generator under asymmetrical operation state.Negative sequence current component produces negative sequence rotating magnetic field.The phenomenon of loss,temperature rise and vibration are deepened,and then will make the armature current and voltage asymmetry.The electromagnetic force of the generator is also changed.The operation state of the large synchronous generator in power system is closely related to the stability and performance of the system.Therefore,it is necessary to analyze and calculate the characteristics,internal magnetic field and electromagnetic force of large Turbo-generator.The problems of generator and power system are analyzed in the condition of asymmetric operation,and 1200 MW large half speed turbine generator is taken as the research object,the influence of negative sequence magnetic field on the electric quantity of the generator is analyzed,the variation law of generator voltage and current and harmonic analysis are obtained.The variation of the electromagnetic force in the generator under different asymmetrical conditions is given.The reasons for these changes are analyzed in detail.Finite element model and field circuit coupling model under asymmetric load ware established.According to the symmetrical component method as the theoretical basis,port network equivalent circuit model are established in asymmetric condition.Using the finite element simulation results,the asymmetrical condition of current and voltage waveform and harmonic analysis are obtained.The variation rules of excitation current and negative sequence reactance are summarized.The results showthat the generator of electrical quantities was changed with the degree of asymmetry.At the same time,the voltage and current of the generator are analyzed by using port network equivalent circuit model,and the results are compared with the finite element simulation results.Using the coupled finite element model of turbine generator rotor radial magnetic Airport Road,different operating conditions of asymmetric density and electromagnetic force are obtained,and the results of the harmonic decomposition show that the influence of asymmetric operation of generator rotor surface electromagnetic force,there is a great change in the air gap magnetic flux density due to the asymmetric operation. |
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