Analysis Of Electromagnetic And Temperature Fields In Broken Strands And Calculation Of Steady Fields In End Region For Large Synchronous Generator

Large turbo-generator is the main power generation equipment in grid, and its health affects the safe operating of power systems directly. As one of the common major failures in this kind of machine, broken strands influence generator operating electromagnetic parameters and loss distribution obviously, which expressed as the variation of temperature. Therefore, it has important theoretical and practical significance to study the electromagnetic and temperature evolution after broken strands. Flux density at the end of large turbo-generator complex end is relatively high, and eddy current losses in various structural components are large and difficult to be determined, which may cause local overheating and affect the reliability of motor operation. Thus, it has an important practical significance for loss analysis and temperature calculation on large machines end components.Firstly, take a 150MW turbo-generator as an example, based on the depth analysis of eddy loss theories within electrical machine, the model for stator bar eddy loss numerical calculation is established, in which the skin effect is considered. Through the two-dimensional electromagnetic field calculation in stator slot, the current density distribution in stator bar with broken strands is analyzed comparing with that in the normal ones, and the varition lows of eddy loss distribution and its values with broken strands number are proposed. Considering the transposition of stator bar, the eddy losses in bar with broken strands at different positons in different cross-sections along the axial direction are studied. Secondly, the three-dimensional temperature field calculation model for stator within a tooth region and axial half-segment is established, and the heat sources are calculated from the electromagnetic fields analysis in machine with broken strands. After the determinnation of heat transfer conditions and considering the eddy loss distribution in bar with broken strands, the three-dimensional temperature field in stator slot is calculatd and analyzed. Furthermore, the influences of broken strands number and position on temperature distributions are studied, and variation of extreme temperature positons and values are obtained.Finally, according to a 200MW turbine-generator structure, considering the the electromagnetic properties of different end components, the three-dimensional model for whole region machine end electromagnetic field analysis is proposed. Through the two-dimensional electromagnetic field iterative calculation, the stator current and core segment surface boundary condition are obtained, and the three-dimensional end electromagnetic fields in lage turbo-generator with rated-load and non-load are analyzed by using finite element method. Based on this, the eddy losses in different end compents are obtained. After the determination of heat conductivity coefficient of stator windings equivalent model, a three-dimensional temperature field calalution model for stator end is established, by which the temperature distribution in stator end is studied.From above study work, a series of conclusions are obtaiened, which could provide a theoretical basis for the initial fault diagnosis of brken strands in stator bars through temperature detection, also may supply a helpful reference to the study on end components of lage electrical machines.