Calculation Of Magnetic Field And Eddy Current Losses In End Zone Of Large Turbogenerator At Operation Under Leading Power Factor

Power system is a modern large power grid that takes the high-power station, the large unit and the high-voltage as the symbol. With the increment of long distance high-voltage transmission lines and power supply cables, as well as the increment of peak to valley ratio of electric network, charging reactive power is surplus in valley period. Owing to this surplus, the voltage of some load-center substations is too high, additional loss is increased, and electric energy is debased, even power equipment's operating security is endangered. It is a safe, simple, economic and effective method to solve this problem for generators at operation under leading power factor. The leakage magnetic flux in end zone of turbogenerator will be enhanced for turbogenerator at operation under leading power factor, and the eddy current losses in end zone will also be increased. So the thermal problem aroused by the increase of the eddy current losses in the stator iron core edge and end structures has become an important factor that endangers the normal operation of generators. It is well known that material quality, structural shape of end zone and the eddy current distributions are very complex. The problem of magnetic field in end zone of turbogenerator at operation under leading power factor was put forward many years ago, but it hasn't been solved perfectly.In this paper, taking formula of 3D FEM using A,φ-A to establish 3D end electromagnetic field's mathematic model of turbogenerator at operation under leading power factor. The model combines end zone with stepped stator core, expands solved region into the stator and the rotor core. The end structure's spatial location, the actual shape and their influence on end field calculation are considered accurately. Then the physical model of end zone of turbogenerator is established. Taking QF-150-2 air-cooled turbogenerator for example, magnetic field and the eddy current losses in end zone of turbogenerator are calculated at no-load, full-load and operation under leading power factor. The results can not only provide the theory proof for improving the design and operation of air-cooled turbogenerator, but also provide the basis for analyzing and calculating the thermal problem of air-cooled turbogenerator under various operation modes.