the input mechanical power of a single alternator is
increased,its RPM increased but in case of an alternator
synchronised with grid its RPM does not increased with
increase of input mechanical power. why?
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Answer Posted / ck misra
when the mechanical input to an alternator connected to
grid is changed it temporarily does increase the speed(RPM).
But an increase in speed means consequent increase in
frequency(as N=120f/P and P being the no. of poles is
constant)of the alternator.Now we know that the voltage and
frequency of grid busbar(what we call infinite busbar)are
constant(off course within some tolerance limit)and the
whole system has large electrical inertia which tends to
oppose any change in voltage level or frequency. So the
alternator is pulled back to synchronism by the grid.
BUT in case of stand alone alternator there is nothing to
pull the alternator back to synchronism and we can increase
the speed with a consequent rise in frequency....
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