Analysis On Electromagnetic Force And Vibration Characteristics Of Generator End Windings Under Mechanical And Electrical Faults

The stator end winding will endure electromagnetic force with the united impaction of periodic current and magnetic field,thus the corresponding variable stress and vibration will be brought.After a long time of repeated action frequently,the end winding insulation wear and fatigue damage will happen,which will furtherly result in the accident.In addition,most generators works with static eccentricity.And rotor winding inter-turn short circuits occures high-frequently in actual operation.They both can influence the electromagnetic force and mechanical response of the end winding.Therefore,it has important academic significance and practical application value to comprehensively analyze the electromagnetic force and mechanical response of the stator end winding before and after such single fault and composite mechanical-electrical faults.In this paper,electromagnetic force incentivation and mechanical response characteristics of end winding before and after single fault of air-gap static eccentricity and rotor winding inter-turn short circuit,as well as the composite electrical-mechanical fault for generator are analyzed by theoretic analysis,simulation and experiment.The main work and innovative achievements of this paper are as follows:(1)The influence of the inter-turn short circuit components of the rotor excitation winding on the air-gap magnetic motive force is analyzed,as well as the influence of eccentricity factors on the magnetic permenance.The analytical expression of the end winding electromagnetic force in four conditions is derivated.It provides a theoretical basis for end winding vibration characteristic analysis in normal operation and fault status.(2)Physical models and external circuit models of generators with a pair of poles and three pairs of poles are established in the Ansys Electromagnetics software for 3D trantient finite element simulation,and the flux density is obtained as well as the force density.And the end winding electromagnetic force in axial,radial and tangential direction are calculated through coordination transform and integral calculation.Furtherly,the frequency components and amplitude variation characteristics of electromagnetic force in different state are obtained,and windings are found which have the larger force amplitude.Meantime,the impaction of pole number on the frequent componets,and influence of eccentricity ratio and eccentricity angle on the amplitude is discussed.It provides reference for vibration wear detection of end winding and control of electromagnetic force.(3)The stator winding model and its electromagnetic force volume density data is imported into Transient Structural module to reallize electromagnetic-structual coupling calculation.The characteristics of the maximum von-Mises stress and deformation of a single coil and the involute part's different position are obtained.The three directional vibration data of specific point is acquired,and the varing characteristics with different faults is analyzed.The fatigue damage and vibration wearing distribution rule is acquired.Meantime,the experimental verification is made on fault simulators of one-pair and 3-pair poles through the vibration data measurement.It provides a foundation for the reverse suppression of fatigue damage and insulation wear in the end windings.The research results have important theoretical and practical guiding significance for the prevention of wear failure,targeted reverse optimization design and manufacturing process improvement of large capacity actual unit end winding.