Calculation Of Eddy Current Losses In The End Structures And Circulating Current Losses In The Stator Bars Of Turbogenerator

Turbogenerators become more and more popular with lots of users as their many merits, for example, simple construct, high reliability and so on. As the increasing of the capacity of the turbogenerator, the eddy current losses in the end structures and the circulating current losses in the stator bars caused by the leakage reactance of the end region increase correspondingly, and this becomes an unneglectable problem in the generator's design. Taking an air-cooled turbogenerator of 200 MW as an example, the eddy current losses in the end structures and circulating current losses in stator bars are studied profoundly. Firstly, the eddy current field of the turbogenerator'end region is calculated. The physical model of the end region is built, which includes press fingers, copper shield, press board and so on. The nonlinearities of materials are modified by effective permeability. The values and the spatial location relations of the magnetic potentials for the stator and rotor at the rated load are determined by iteration. The eddy current field of end region at rated load is calculated, basing on which the eddy current and eddy current losses in the structures are computed and analyzed detailedly.Secondly, the impact on the circulating currents in the windings transposed by 0 /360/0and 0 /540/0is analyzed in the paper. The analytical method for the calculation of circulating current and circulating current loss is discussed. The magnetic field of end region is divided into self-induce leakage and mutual-induce leakage, and the analytical method of calculating the circulating current and circulating current loss generated by them is studied respectively. In order to calculate circulating current and circulating current loss current accurately, the mathematic model is established by node-voltage-method basing on numeric calculation of end magnetic field. And then the circulating current and circulating current loss of the model machine are calculated and compared by analytical method and numeric method.Lastly, the numeric calculation for temperature field about the end region of air-cooled turbogenerator's stator bars is investigated initially, and a FEM model about temperature field including a single end stator bar and a section of stator iron core is built. The coefficients of heat transfer for each surface and equivalent coefficient of heat conduction for stator bar are determined by theories of heat transfer and fluent similarity, and then the temperature distribution of end coil is gained, which provides some references for exactly calculating the temperature field of turbogenerator's end region.