| A turbo-generator which produces electric energy is one of the key equipment in thermal power plants, gas-stream combined power stations and nuclear power stations. As is well known, the development of turbo-generator plays an essential role in modern power systems. Among cooling modes of turbogenerator, air-cooled mode is widely used because of its advantages, such as low cost and convenient maintenance. Taking a 150 MW air-cooled turbo-generator as an example in this paper, detailed analyses of electro-magnetic parameters, losses as well as stator temperature rise were given when magnetic slot wedges were used in rotor and stator respectively. Meanwhile, the influence of using magnetic slot wedge in generator was also discussed. Above all, the conclusions present theoretical basis for design of generator.Because the turbo-generator owns relatively large diameter and high speed,so slot wedge needs to withstand large centrifugal force caused by high speed rotation. In the operational process of the turbo-generator, the rotor slot wedge can overcome the centrifugal forces. In the air-cooled turbo-generator whose excitation winding is cooled directly, the rotor wedge has been become one part of cooling path of excitation winding. In addition, the rotor slot wedge also have similar effect of the damping winding. Usually, the materials of the rotor wedge in the large capacity turbo-generator are the nonmagnetic aluminum alloy or aluminum bronze. Nowadays magnetic slot wedges have been widely used in the high-voltage motors or in the hydro-generators, which mainly due to the reduced harmonic values of the air-gap and the improved efficiency of the generator.However the magnetic slot wedge has not been widely applied in the turbogenerator nowadays. Under the above background, the paper makes thoroughstudy about the relevant scientific problems in the magnetic slot wedge used in the turbo-generator.Instead of the usual aluminum alloy slot wedge or the duralumin slot wedge,the low-intensity slot wedge, as well as the Fe-Cu alloy slot wedge which is high-intensity magnetic and electric, were embedded in the opening slot of the rotor. By establishing the mathematical model of 2D electromagnetic fields of the generator, the saturation reactance values were calculated with these three different materials, and the corresponding relationships of the reactance were also given. Furthermore, adopting the time-step finite-element method, the rotor losses were calculated respectively compared with aluminum alloy slot wedge and low-intensity alloy slot wedge as well as magnetic and electric conductive slot wedge. Meantime, values of the stator iron loss and the rotor loss were calculated when using these three different materials and when using different shapes of rotor alloy slot wedge respectively.The influence of different slot pitch coefficients of rotor on electromagnetic field was investigated, and the mathematical models of the turbo-generator were established with different slot pitch coefficients. The electromagnetic fields with different slot pitch coefficients were also calculated respectively using three different materials which are non-magnetic slot wedge and low-intensity alloy slot wedge as well as Fe-Cu alloy slot wedge which is magnetic and electric.Meanwhile, applying different slot pitch coefficients, the laws of the synchronous reactance values of the generator and magnetic field waveform as well as loss were also analyzed when slot wedge materials were changed.The single-slot mathematical model of a 150 MW air-cooled turbo-generator was established in consideration of many factors. Based on the single-slot model,the distribution laws and the influential factors of the transverse leakage flux in the slots of the stator were studied. Then, distributions of strand eddy current density as well as strand eddy current loss influenced by the stator horizontal magnetic leakage flux are also analyzed. In addition, the analytic expression of eddy current with inequality strands caused by transverse magnetic flux leakage is also given.A mathematical model of the 3D temperature field constructed by a single stator slot wedge with one lamination segment was established, and then thedistributions of temperature field and fluid field of the stator were calculated under three different conditions, that is, without using magnetic slot wedges,using stator wedges at different positions, as well as using magnetic slot wedge in the rotor. According to the above mentioned analysis, the maximum temperature rise of the stator can be improved by using the magnetic slot wedge of the rotor to a certain extent. In addition, the distributions of temperature field were analyzed when magnetic slot wedges were used in stator and in rotor.Through the contrast analysis, the conclusion is that the magnetic slot wedge is more suitable for the rotor.Through in-depth study of the above scientific issues, the application regularity of the magnetic slot wedge used in a large turbo-generator has been achieved, and the determination method of the optimal rotor slot pitch coefficients has been also obtained. In the meantime, the variation laws of the stator transverse leakage flux and the strand additional eddy losses, as well as the instantaneous temperature field of the complete machine have also been achieved.The above results obtained could provide theoretical basis for design and production of the large turbo-generator. |
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