Research On Negative Sequence Current Loss And Heat Of Turbo-generators

Large turbo-generator is the high technical equipment for electric power which is always considered as the heart of power system.And it becomes the development goals of each domestic and foreign power generation equipment companies.Beside that,its key technology has been paid close attention by international academia and engineering.With the development of the generators,electromagnetic and thermal load increase as well.This could cause local overheating,abnormal downtime,or threat to power system security.Meanwhile,as for large turbo-generator,it is essential to be operated in certain asymmetrical conditions,and the damage by such negative sequence current could do,will be more severe.Hence,it is vital that conducting research on the current loss and heat,that could increase the generator negative sequence capacity and decrease the current damage to the rotor,in process of analyzing the asymmetrical operation characteristics of turbo-generator.In this dissertation,3D FEM model of temperature field is constructed for a turbo-generator based on the basic theory of electromagnetism and thermodynamics.Then,the negative-sequence temperature field calculations of different conditions,that the negative-sequence components equal 2%,6% and 10%,are carried out.The distribution laws of negative sequence temperature rise for different turbo-generator types are studied carefully under different negative sequence conditions.According to the negative-sequence experiments and practical operation cases,the main influencing factors are summarized,and the problems of negative sequence capability are pointed out.Based on short-circuit current results,the equivalent negative sequence effect of DC current component is analyzed,and a series of equivalent negative sequence affections are obtained.Then,this dissertation proposes an improved transient negative-sequence calculation formula for a large-capacity turbo-generator system under unbalanced network conditions,due to the disadvantages of traditional transient negative-sequence ratings.According to the inherent relation between rotor heating and generator imbalance capability,the DC component is added to the improved transient negative-sequence formula in the paper.The rotor eddy current loss FEM calculations are carried out to deal with having different cross slot distances,different polar damping structure and using different wedge materials,under different negative sequence conditions for turbo-generators.The influence of different cross slot distances on the eddy current loss are analyzed and calculated.The eddy current loss distribution comprehensive comparisons with without cross slot,9 cross slots and 19 cross slots of each pole are studied.Moreover,the loss distribution effects caused by different damping winding structures are also discussed.The eddy current loss distribution comprehensive comparisons with without slot wedge,2 damping slot wedges and 4 damping slot wedges of each pole are studied.Furthermore,the influence of different slot wedge materials on the eddy current loss are analyzed and calculated.The change rules of eddy current loss distribution caused by different negative sequence conditions,different cross slot distances,different polar damping structures and different slot wedge materials are also got.This dissertation also copies with the rotor negative-sequence temperature rise of turbo-generators based on the analysis results of eddy current losses.The rotor temperature fields are calculated when different cross slot distances are adopted and the different cross slot distances' effects on the rotor temperature field,without cross slot,9 cross slots and 19 cross slots of each pole are researched.Furthermore,the effects on big tooth surface temperature distribution,causing by the damping slot wedges,are analyzed deeply.The temperature rise distribution comprehensive comparison with without slot wedge,2 damping slot wedges and 4 damping slot wedges of each pole are carried out.The rotor temperature fields are calculated when different slot wedge materials are adopted and the different slot wedge materials' effects on the rotor temperature field are researched as well.And the change rules of rotor temperature rise caused by different polar damping structures and different slot wedge materials are pointed out.At the same time,the corresponding application suggestions are also given,which could provide the theoretical basis and reference for the relevant follow-up researches.