Research On Characteristics And Performance Of Detection Method Of Inter-turn Fault Of Excitation Winding Of Turbo-generator

Inter-turn short circuit fault of excitation winding has a high incidence in turbo-generator,which can cause magnetic field imbalance and lead to excessive vibration,especially under the extreme conditions of strong excitation.Sensitive,fast and reliable diagnosis of the fault can reduce fault finding costs,aid ma intenance decisions and prevent deterioration.Therefore,it is necessary to conduct an in-depth study on online detection methods to provide the optimal technical choice for on-site online diagnosis.The main work of this paper is as follows:(1)Taking a turbo-generator with a pair of poles as an example,the influence of normal excitation winding and inter turn short circuit fault on the relevant harmonic content in the main magnetic field is analyzed,the characteristics of air gap synthetic magnetomotive force under no-load and rated load conditions are studied,and the unbalanced magnetic pull of rotor and the circulating current of parallel branches of stator winding are calculated.Based on the characteristics that the larger the excitation current is,the more serious the asymmetry is,it is pointed out that the generator with fault operation is more harmful under forced excitation conditions.Therefore,the variation law of unbalanced magnetic pull and stator circulation and the asymmetric level of air gap magnetic field under false forced excitation and normal forced excitation conditions are analyzed.(2)Taking a 300 MW turbo-generator as the research object,the two-dimensional finite element model is established by using ANSYS software,and the cou pling simulation platform is built.Through finite element electromagnetic transient simulation,different degrees of inter turn short circuit faults of excitation winding are simulated under no-load condition and rated load condition of the generator respectively,and the unbalanced magnetic pull and stator winding circulation under three extreme conditions of no-load false forced excitation,rated load false forced excitation and forced excitation caused by different degrees of three-phase short circuit of power grid are analyzed and verified,so as to determine the forced excitation state that is most harmful to the generator,provide safety risk assessment and maintenance decision support for steam turbine generator in fault operation.(3)Aiming at the three on-line detection methods of inter turn short circuit of excitation winding based on the principle of magnetic field induction,namely detection coil method,U-shaped detection coil method and rectangular detection coil method,the diagnosis principle of each detection method is studied.Through finite element simulation,the rated load condition of turbo-generator is simulated,interturn short circuit faults of different degrees are set at different positions of rotor,the induced voltage of three detection coils is obtained,and the harmonic content characteristics of voltage and the variation law of waveform pulse in time domain are further extracted.Finally,the comprehensive performance comparison of the three detection methods is completed,which provides an objective basis for users to choose high-performance online diagnosis methods.