| With the development of large steam turbine generator units in China towards high parameters and large capacity,new challenges are put forward to the safety and reliability of generator units.Rotor crack is one of the major hidden troubles of turbo generator set,which will pose a major threat to the safe operation of the generator set and should be avoided as much as possible.Based on this,this paper will study the generation mechanism of cracks in the rotor of large turbo-generator,and put forward the diagnosis method of cracks in the rotor of generator,which provides an important theoretical basis and technical means for the prevention and early detection of cracks in the rotor.First of all,based on the finite element method,the mechanical analysis model considering nonlinear contact and nonlinear constitutive is established.Under different working procedures,rotating speed,temperature rise and torque conditions,the life and death element technology and multi load step method are used to calculate the structural stress.Combined with Goodman line,the fatigue characteristics of the structure are analyzed,and the mechanism of the generator rotor crack is revealed.Secondly,the dynamic characteristics of multi span rotor with cracks are studied.The dynamic model of multi span rotor including low pressure cylinder rotor,generator rotor and collector ring rotor of steam turbine is established.The effects of cracks in different positions and different degrees of damage on the vibration characteristics of rotor in transverse and torsional directions are studied,which provides theoretical basis for crack diagnosis and location of multi span rotor of large steam turbine generator.Thirdly,the method of eliminating and diagnosing the crack of turbo generator set is put forward.The typical faults which are easy to be confused and coupled with the rotor crack faults are classified into mass unbalance faults,rub faults and thermal unbalance faults.The relationship model of each fault type and two frequency components with four working condition parameters is established,forming a systematic diagnosis method for the rotor crack faults of turbo-generator,which provides the field diagnosis for the rotor crack faults Effective means.On the basis of the above research,a vibration data acquisition test system is set up on the site for the rotor of 600 MW steam turbine generator set in Turkey Biga power plant.The troubleshooting test and dynamic balance test are carried out to realize the diagnosis of the rotor crack.The flaw detection results also verify the mechanism of the crack. |
