CONTROL OF EFFORTS IN TIGHTENING PRISMS OF CORE IN POWER GENERATORS WITH USING CAPACITIVE SENSORS
Anatolii S. Levytskyi · Praci Institutu elektrodinamiki Nacionalanoi akademii nauk Ukraini · 2019
The statistics of the last decades shows the fact that the stator cores have become the main unit responsible for limited service lifetime and low reliability indices of large turbogenerators.The most distributed defects are as follows:-self-unscrewing of pressing rings fastening nuts, -tears off of threaded tails of stacking ribs, -loosening of the core radial connections with the stacking ribs in the stator top part, bends and tears off in cantilever sections of active sheet steel in the teeth zone, -emerge of local overheating due to pressing down fingers insulation covering abrasion and fracture determination of glued end packages.These defects in some cases caused heavy damages of the stator winding.Due to decreasing of the stator unit operation reliability carrying out of expensive repairs in the plant conditions or the stator replacement at site of installation as soon as calculated service lifetime (or in the case of the stator core service ability) end.There is misunderstanding in power processes in the stator cores.Despite the application of method of "short time replacement" of stator core-and-winding assembly by some of leading firms the main cause of the paradox remains unknown.We have performed the analysis of the extensive statistical materials and, the most important thing is new measurements of axial vibration components and variable mechanical stresses in the stator core at mounting places of large turbogenerators.The last revealed that the main cause of the paradoxical situation is in misunderstanding of force processes in the stator core.It was found that in the stator core the complex of internal forces of the same order as the forces of magnetic tension in air gap emerges.Therefore designing conceptions and maintenance of large turbogenerators shall be reviewed with allowance for those forces.Those electromagnetic ("ponderomotoric") forces emerge as a result of electric current interaction.According to the classic theories in the coreless coil with electric current such forces has axially pulling and radially pushing character.The same phenomena originate in 21,