Turbo-generator Excitation Winding Inter-turn Short Circuit Fault Compound Characteristics Analysis And Diagnosis

China's energy transformation has been accelerating in recent years,and the installation of new energy installed capacity is developing rapidly,the traditional energy represented by thermal power generation still occupies a dominant position.In the next ten years or even twenty years,the installed capacity and power generation of thermal power generation will also account for half of China's total energy,the operation burden of large turbogenerator units becomes heavier and the failure rate of units increases.Especially for the excitation winding which accompanies the high speed rotation of generator rotor for a long time,the inter-turn short circuit fault occurs frequently.The excitation winding inter-turn short circuit fault may cause more serious faults such as rotor grounding if not handled in time,causing damage to the generator body.It is of great significance for the safe and stable operation of turbo-generator units to study the fault characteristics of excitation windings inter-turn short circuit and find effective fault diagnosis methods.In this dissertation,the electromagnetic,thermal and mechanical characteristics of turbo-generator excitation winding with inter-turn short circuit fault are studied in detail.On this basis,the corresponding diagnosis methods are proposed to improve the diagnosis and fault location accuracy of excitation winding inter-turn short circuit fault.The main work and achievements are as follows:1.Study on electromagnetic characteristics of excitation winding interturn short circuit fault.The finite element model of the two-dimensional solution domain of a turbo-generator stator and rotor is established.The air gap magnetic field distribution characteristics of generator with different degrees and locations of excitation winding inter-turn short circuit fault are obtained.Maxwell stress tensor method is used to calculate the unbalanced magnetic pull on the generator rotor under different excitation winding inter-turn short circuit faults.The variation of air gap magnetic field and unbalanced magnetic pull of rotor with fault degree and fault location is summarized.It is pointed out that the unbalanced magnetic pull of the rotor is an important reason for the abnormal vibration of the rotor.2.Study on thermal characteristics of excitation winding interturn short circuit fault.The three-dimensional solution domain of turbogenerator rotor is established by finite element method,and the temperature distribution characteristics of generator winding with different degrees and locations of excitation winding inter-turn short circuit fault are obtained.Based on the calculation results of temperature field,the thermal stress of unbalanced distribution in the rotor is obtained by sequential coupling method.The variation of rotor temperature field and thermal stress with fault degree and fault location is summarized.The unbalanced distribution of thermal stress causes a difference in the amount of expansion on each side of the rotor.It is pointed out that the thermal bending of the rotor is another important factor causing the abnormal vibration of the rotor.3.Study on mechanical characteristics of excitation winding interturn short circuit fault and diagnosis method based on rotor vibration characteristics.Based on the flexible structure of the rotor,a rotor bending solution model is constructed,and the unbalanced magnetic pull and unbalanced thermal stress are equivalent.Starting with the motion equation of the rotor,the Newmark implicit integral method is used to solve the motion equation,and the rotor axis motion trajectory and the rotor vibration response are obtained.The rotor vibration law of excitation winding inter-turn short circuit in different fault degree and location is summarized.An excitation winding inter-turn short circuit fault diagnosis method based on rotor fundamental frequency vibration amplitude and phase angle is proposed.This method can realize the diagnosis of excitation winding inter-turn short circuit fault and has the function of fault location.4.Study on diagnosis method of excitation winding inter-turn short circuit fault based on stator double detection coils.The distribution of excitation magnetomotive force under the excitation winding inter-turn short circuit fault of a turbo-generator with two pole pairs is analyzed.According to the fractional harmonic magnetic field generated by the excitation winding inter-turn short circuit fault in the generator,a fault diagnosis method for installing detection coils on the top of two stator core teeth separated by one pole distance is proposed.The electromotive force induced in the detection coil has characteristic subharmonics consistent with the main magnetic field.The validity of the stator double detection coils method is verified by the FEM field-circuit simulation model,which can realize the excitation winding inter-turn short circuit fault diagnosis and location of the generator under various operating conditions.