ANALYSES ON COUPLED BENDING AND TORSIONAL VIBRATIONS EXCITED BY ELECTROMAGNETISM IN AIR GAP OF A GENERATOR SET ROTOR SYSTEM

摘要

The vibration of generator set excited byrnelectromagnetism is one of the key technical problems inrnthe process of developing large turbogenerator set andrnlarge power system. As developing toward the large-scalerngenerator set, the vibration of generator set is becomingrnmore and more serious. Generator set is a kind of typicalrnsystem with mechanical and electrical interaction. There isrnnonlinearity in mechanical elements and electromagneticrnelements, so plenty of nonlinear dynamics phenomenarnexist in the vibration of generator set, such as coupledrnvibration, multi-resonance and so on. Many studyrnproductions[1-4] indicate that mechanical and electricalrninteraction is extraordinary strong when generator set isrnrunning. Mutual coupling and mutual inducement betweenrnmechanical and electrical lead to more strong vibration. Sornwe should pay more attention to this problem.rnThe feature of mechanical and electrical interaction isrnthat there are uniform equations that coupled vibrationrnequations of rotor system with voltaic equations ofrngenerator set. That is to say it is inseparable relationrnbetween rotor system dynamics and transient theory ofrngenerator set. There are two basic difficulties aboutrnmechanical and electrical interaction. One is how tornestablish the model accurately. And the other is how tornsolve the model effectively. The two difficulties are tried tornstudy preliminarily in this paper. The paper describes thernexpression of magnetic permeability of air gap. And thernenergy of electromagnetic field is obtained.rnElectromagnetic moment, radial electromagnetic forces,rntorsional electromagnetic stiffness and radialrnelectromagnetic stiffness forced on the rotor of generatorrnset are got too. The rotor system of generator set isrnsimplified as the model of Jeffcott rotor which is a singlerndisc with rigidity supporting. Based on the balance ofrnforces and moments of Jeffcott rotor, the equations ofrncoupled bending and torsional vibration are established.rnThe equations are nonlinear, so their accurate analyticrnsolutions are difficult to obtain. Using the numericalrnintegral method named Newmark − β , the discreternsolutions of the equations are acquired. The Newmark − β method is improved through appendingrncalculated damping. And detailed calculated steps arernenumerated at last.