Study Of Transposition In Stator Bars Of Large-scale Hydro-generator

With the deepening of the worldwide energy crisis and environmental pollution, the exploitation and the development of clean energy has become an important problem to researchers today. Hydro power is a vital part of clean energy, an effective measure to alleviate the energy crisis is to vigorously develop hydro power.With the advances in turbine design and its manufacturing technology, electric capacity and power density in large-scale hydro-generators has increased. The improvement of its efficiency and the reduction of its losses must be considered in the design and manufacturing process of the generator. In the design of large-scale hydro-generators’stator bars, the stator bars generally use two rows of the strip by the number of strands in parallel in order to reduce the impact of the skin effect. The leakage magnetic field in slot portion and the end portions of bar will generate circulating currents between parallel strands, bringing the circulating current losses. The circulating currents in stator bars will lead to an uneven temperature rise between the strands which destroy the insulation of the bar. At the same time, circulating current losses have a negative impact on generator efficiency and will shorten its service life. The electric potential of the leakage inductance of the slot portion will offset each other by twist strands in the slot portion for360degree. In this way, circulating current losses can be reduced. This kind of stator bars named Roebel bars. But in Roebel bars, the leakage magnetic field in end portions still persists and generate circulating currents between the strands, so we the need to study the leakage magnetic field in slot portion and end portions.In order to reduce the circulating current loss in stator bars, we need to focus on where this came from. We can start from leakage magnetic field in slot portion and end portions. This paper describes the calculation of the loss of the strand loop method and potential leakage inductance of circulation. With detailed descriptions of circulating current loss formula of the lack of the leakage inductance potential transposition method, empty and extend transposition method. The circulating current loss formula of leakage inductance potential method has been verified. By using the finite element method, a two-dimensional model of the stator bars in the slot portion and end portions has been established. The magnetic field distribution in this model is approximate to the leakage inductance potential method. By performing the stator bars transposition study, it has been found that with the changes of transposition in stator bars, the copper loss changes. Therefore, this paper presents that the copper loss in stator bars as a factor of the consideration in the optimization of the stator bars’ transposition.In this paper, a set of large hydro-generator transposition optimal design software by using MFC engineering software on the basis of the leakage inductance potential method and research projects has been developed. The calculation and analysis of the circulating current loss of multiple transpositions in two hydro-generators has been done by using this software. Test data in other papers and calculation results from this software were compared. It shows that the methods which used in this paper are correct.