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In most of the text books it is described that a turbogenerator is absorbing MVARS from the system when operating in leading zone of the generator reactive capability region. Generator is designed to provide power to the system and not to take power from the system. If someone can kindly explain this phenomenon to me(absorbing VARS?)!
Again in some of the threads a lot is mentioned about under-excited operation of a turbogenerator. Most of the textbooks have a mention as many authors have explained that in the lagging region, the stator flux directly opposes the field flux whereas in the leading region the stator flux assists the rotor field flux. Hence the terminal voltage is increased. The vectorial diagrams prove what it is said in the text-books and what is said by authors. But what happens physically? How does the armature reaction which was in direct opposition in the lagging region, starts assisting rotor flux in the leading region? Vectorially it is proved and I can satisfy myself. If one of the knwoledgable authors on this forum can throw some light on what practically happens, it would be great.
As one of the authors has explained like this :-When one reduces the excitation on the rotating magnetic field, the flux field of the rotor "shrinks". Which allows the flux field of the armature to "expand." The flux distributions get "disturbed" when the excitation is reduced too much, and this is what causes the concentrated heating which leads to the unwanted growth (things grow with heat!) which causes unwanted things to happen.
Agreed that the rotor flux "shrinks", but the magnitude of the flux on the stator depends on the field strength, so how does the armature flux "expand". If the author can kindly explain this I shall be grateful. The latter part will be clear then, that if there is expansion of flux, there will be core saturation, flux fringing and hence end winding heating.
Again in some of the threads a lot is mentioned about under-excited operation of a turbogenerator. Most of the textbooks have a mention as many authors have explained that in the lagging region, the stator flux directly opposes the field flux whereas in the leading region the stator flux assists the rotor field flux. Hence the terminal voltage is increased. The vectorial diagrams prove what it is said in the text-books and what is said by authors. But what happens physically? How does the armature reaction which was in direct opposition in the lagging region, starts assisting rotor flux in the leading region? Vectorially it is proved and I can satisfy myself. If one of the knwoledgable authors on this forum can throw some light on what practically happens, it would be great.
As one of the authors has explained like this :-When one reduces the excitation on the rotating magnetic field, the flux field of the rotor "shrinks". Which allows the flux field of the armature to "expand." The flux distributions get "disturbed" when the excitation is reduced too much, and this is what causes the concentrated heating which leads to the unwanted growth (things grow with heat!) which causes unwanted things to happen.
Agreed that the rotor flux "shrinks", but the magnitude of the flux on the stator depends on the field strength, so how does the armature flux "expand". If the author can kindly explain this I shall be grateful. The latter part will be clear then, that if there is expansion of flux, there will be core saturation, flux fringing and hence end winding heating.