Research On Electromagnetic And Temperature Fields Of Large Turbo-generator With Different End And Cooling Structures

As the important energy conversion device in power station, the abnormaloperation of the turbo-generator not only have a serious effect to the power plantand power system security, but also bring huge economic losses. When the powersystem load is low, the surplus of reactive power in power grid will cause voltagerise. In order to ensure the power quality, it requires the generator to have the abilityof leading phase operation to absorb the excess reactive power in power grid. Theend magnetic field will increase with the increasing of the phase depth, which willcause the serious fever end in the end metal parts. Besides, the blocking failure andrun off the water occurred in the water cooled generator will cause the coolingability in the stator decreased, which will cause the high local temperature. All ofthe above problems will impact the safe and stable operation of the generator.Therefore, it is important to research the electromagnetic and temperaturedistribution of turbo-generator which will reduce the generator loss, improve thetemperature distribution, and extend working life of the generator.In this thesis, the influences of different end stator step packets, end windingdimensions and the phase depth on end magnetic field distribution and eddy-crrentlosses are studied using three dimensional transient electromagnetic field and theeffect of the blocking and water break failures of hollow strands on the stator localtemperature variation are investigated. The calculated results of the3Delectromagnetic field and temperature field were verified by the test values, whichverify the correctness of the computational method.First of all, for a water-hydrogen-hydrogen cooled turbo-generator endstructure, the end electromagnetic field calculation model including four stator steppackets was established. By using the3D time-stepping finite element method(FEM), the magnetic field distribution and iron losses of the stator step packets wereobtained. The air gap magnetic flux density for various axial positions in end regionwas analyzed and the effect of the end leakage magnetic field on the iron losses inend stator step packets was comparatively studied. The influences of the end statorpackets with ladder structure and without step packes on the magnetic flux densityin the teeth were studied. The magnetic field distribution and end losses withdifferent step angles were comparativly analyzed. The obtained conclusion willprovide important reference for the structure optimization design in the end part.Sencondly, the influences of stator and rotor end winding dimensions on endlosses and electromagnetic distributions were studied. A2D iterative calculation wasdone with the power factor and the phase voltage as the target of convergence, and the field current and angle were obtained. The effect of the length of stator endwinding and rotor end winding in the line segment parts on the end losses wascomparativly analyzed, and the influence of different end winding dimensions onend air gap magnetic was studied. The changes of magnetic flux density, also theaxial and radial component were investigeted, and the influence degree of the endwinding to stator step packes on iron core losses were analyzed, and also the eddycurrent loss distribution in the end metal parts was obtained.Thirdly, for the increasing losses of the end parts, the changing rules of endmagnetic field and electromagnetic loss with generator running under differentphase depth were studied. Excitation current and power angle under different phasedepth were calculated and analyzed considering the saturation characteristic ofstator and rotor cores. The eddy-current losses and iron losses under different phasedepth were obtained, and radial and axial component of the magnetic flux density inthe press plate, press finger and copper field are analyzed.Lastly, the temperature distribution and thermal aging property with theblocking and water break failures in the water cooled stator windings are researched.Temperature variation law with time under water break fault were analyzed.Considering the complex cooling structure, a three-dimentional conjugate heattransfer coupling analysis modle was established, and the series solid-fluid heattransfer conditions are determined. The cooling capacity of hollow strands wasanalyzed and the influences of hollow strands on strand insulation temperature wasinvestigated. The effects of blocking hollow strands numbers and locations on themain insulation were investigated. A new cooling structure of stator windings wasproposed, and the effects of the new cooling structure on the strand eddy-currentlosses and the impact of new cooling structure on reducing the highest temperaturewith blocking failure were investigated. Meanwhile, the running ability of thegenerator with water break failure were evaluated. Temperature variation law withtime of the cooling water and stator winding were obtained.