On-line Mornitoring And Positioning Of Inter-turn Short Circuit In Field Winding Of Generator

Inter-turn short circuit of generator field windings incidents easily occur and it will cause the field current of the generator to increase,output reactive power to reduce,unit vibration to intensify.If the fault is not handled in time,it may lead to more serious safety accidents.The aim of this study is using the fault characteristic quantities of running generator to realize the online intelligent fault monitoring,eliminate the monitoring of the dead zone in traditional solutions,and discover the small number turns of the early fault.The research focus of this paper are the mathematical model combined with field and circuit,on-line monitoring scheme of fault,location method of fault pole and unbalanced magnetic pull of rotor after fault,which are the cores to realize the on-line monitoring and positioning of field winding interturn short circuit fault.The main research contents and conclusions are as follows:(1)In order to realize the fast and accurate calculation of the interturn short circuit fault of excitation winding,a fault mathematical model is established by using the field-circuit method.Considering the distortion of air-gap magnetic field is small,the inductance parameters of each stator and rotor winding for normal operation are calculated by finite element method and imported to the multi loop equation.And then the steady-state electrical capacity of the generator after failure can be obtained.This method realizes the decoupling of the circuit and the magnetic field equation.For the reason that the two solutions are solved respectively in the calculation process,and the iteration is not repeated,the computational efficiency is improved significantly.The correctness of the method is verified by the comparison between the experimental results and the simulation results.(2)In order to solve the influence of the inherent unbalance current on the detection sensitivity of small turns,a sensitive monitoring scheme based on the inherent unbalanced current prediction is proposed.Based on the field-circuit mathematical model,the short-circuit fault of the excitation winding of er tan and pengshui turbine is calculated,and the sensitivity of fault monitoring is analyzed based on the measured data.The results show that the traditional phase shift superposition monitoring scheme still exists to monitor the dead zones for generators with more fractions and even subharmonic in the inherent unbalanced current.For this reason,the harmonic characteristics of unbalance current caused by stator and rotor anomaly for different pole logarithm generator are analyzed,and the results are verified by experiment and simulation.Based on the simulation calculation of the inherent unbalanced current of stator in different working conditions,the relationship between the total effective value and the excitation current is obtained.And then a fault monitoring scheme based on the inherent unbalance current prediction is proposed,and the sensitivity of the scheme is calculated on the pengshui generator.The results show that this scheme has successfully eliminated the influence of fractional and even inherent unbalanced current on the detection sensitivity of the small turns short circuit,and the sensitivity of fault monitoring is further improved.(3)In order to solve the problem that the magnetic pole position is not realized,the fault positioning method based on the time domain features of unbalance current waveform is proposed.Using the mathematical model for fault prototype unipolar fault is calculated,the results are analyzed,and the relationship among the fault magnetic pole position,fault magnetomotive force,the electromotive force and the phase of fault unbalance current.Therefore,a fault pole online positioning method is proposed based on the stator unbalance current waveform in time domain features and the correctness of it is validated through the fault simulation experiments and prototype.Finally,in order to study the influence of stator winding form on the characteristics of unbalance current time domain,the short-circuit fault simulation of rotor is carried out for the synchronous generator of three stator winding forms,the time domain characteristics of unbalanced current in different stator windings are obtained,and the reasons are analyzed by analyzing the numerical characteristics of inductance parameters of rotor winding inductors.(4)In order to study the mechanical vibration characteristics of the generator after failure,the calculation model,generation mechanism,amplitude and frequency characteristics of the rotor unbalanced magnetic pull are studied comprehensively and deeply.First of all,a rapid calculation model of rotor unbalanced magnetic pull based on multi-loop method is proposed,and the correctness of the model is verified by finite element simulation.The defect of fast and accurate calculation of unbalance magnetic pull of rotor is solved and the effect of short circuit turns and position on unbalanced magnetic pull is studied based on this model.After then,all kinds of air gap magnetic field effects are considered and the influence of fault on the vibration mechanism is explained in detailed by analyzing the fault space air gap magnetic field interaction,and the frequency characteristics of rotor unbalance magnetic pull of generator with different forms of stator winding are obtained.Finally,the unbalanced magnetic pull of the rotor with different active power and excitation current is calculated by the analytical model and the characteristics of unbalance magnetic pull with the change of generator condition are obtained.The conclusion lay a theory foundation for the on-line monitoring of rotor interturn short-circuit fault in the integration of electromechanical information.