Calculation Of Circulating Current And Comparison Of Transposition Models Of Hydrogenerator's Stator Bar

The stator bar of large- and medium-scale hydrogenerators is composed of tens of parallel strands insulated separately in order to decrease the effect of skin-effect. Strong circulating currents within the strands and large additional copper losses are produced in a traditional Roebel bar due to the effect of the leakage magnetic fields in the end region of the hydrogenerator. The circulating currents, additional copper losses and the nonuniform temperature-rise caused become larger with the increase of the hydrogenerator's capability. These phenomena are one of the main reasons for the low efficiency and short life span of the hydrogenerator. Therefore, it is important to pay more attentions to research the stator bar transposition of the hydrogenerator.Firstly, the leakage magnetic fields in the stator slot and the end region are discussed and the cause of formation about the circulating currents is expounded. Then the basic theories and methods for decreasing the circulating currents and their additional copper losses are discussed. The analysis and calculation of circulating currents for different transposition models in a stator bar are analyzed by two methods, the strands loop method and the leakage fields EMF method. Secondly, based on the former research results of the leakage fields EMF method, the induced EMF calculation of the strands of 360°transposition, 360°transposition with a void and less than 360°transposition are summarized. Then the calculation formula about the strands induced EMF of 360o elongation transposition are proposed in detail. Thirdly, a suit of engineering software for the stator bar transposition design of the hydrogenerator is developed by Visual Basic 6.0.To verify the results proposed by the thesis, different transposition models of the hydrogenerator stator bar about several power plants are analyzed and compared synthetically. The correctness and engineering application value of the optimal results are validated by the third party data. At last, some useful suggestions for the design of stator bar are concluded.