Research On The Abnormal Nonlinear Characteristics Of Synchronous Generator

The nonlinear characteristics of turbo-generators under normal and abnormal operating conditions are studied in the thesis through the combination of theoretic analysis and finite element calculation. The nonlinear characteristics under load condition for turbo generators with different structure are first presented. The time-step FEM based nonlinear dynamic model of a single-machine infinite-bus power system is established. The influences of the nonlinear characteristics on stability of the power system are studied. The work and research results are as follows:(1) It is discovered that abnormal nonlinear characteristics commonly exist in turbo-generators with different structures under abnormal operating conditions. It is first presented that there are two factors inducing the nonlinear characteristics of turbo-generators and they are iron saturation and magnetic field distortion. The double-factors nonlinear characteristics have great effect on traditional load-saturation characteristics and a series of new results are obtained through further research.(2) The calculation method of incremental reactance based on finite element method is proposed. From three calculation examples of 135MW, 300 MW and 600MW turbo-generators, it is found that the incremental reactance varies with changes of the power angle, active power and field current.(3) The formula to calculate the local electromagnetic force on rotor iron surface is improved considering the nonlinear characteristics of generators. The electromagnetic force distribution on the rotor iron surface of a 600MW turbo-generator is calculated for its fault analysis. The results first discovered that the force highly concentrates in the region of the first two teeth which locate right next the big tooth, The stress on the sides of teeth is as big as 2.5 times of the average value and this area match with the real fault location. It will be an important reference on generator fault analysis.(4) The time-stepping FEM model for the dynamic analysis of power system is established considering the nonlinear characteristics of internal generators and typology structures of external circuit. The partial differential equations depicting the nonlinear characteristics of generators and constant differential equations describing the dynamic process of power system are combined to realize the simulation of various dynamic process including short circuit faults on the transformer terminal or on the transmission line, cut of faults and reclose of the line.(5) Based on three types of synchronous generator models that are time-stepping finite element model, linear Park equation model and saturated nonlinear Park equation model, the dynamic process of a single-machine infinite-bus power system is...