Answer / mm

real power delivered per phase=VE*(p.f).when excitation is
increased without increasing input to prime mover the real
power remain constant.as per the above equation as
excitation changes pf has to change correspondingly to
maintain real power constant

Answer / k.prakashchandra

If you want to increase the speed more input to prime mover
is required.As the grid is very large ,this will result only
in more sharing of load.You can not change the frequency.If
you increase the excitation, the terminal voltage of gen
will increase ,and you can not increase the entire grid
voltage . This additional voltage will drop in the gen
itself and a small portion of grid ,resulting in more gen
current and increased lagging pf.If the terminal voltage of
the gen is less than grid voltage the power will be
evacuated at leading pf and again more gen current.

Answer / raul

after synchronising, the real power delivered by d
alternator is VI*p.f.........if the input increases, the
real power power will increase, there will b no effect on
speed n frequency........
when excitation changes, the reactive power changes which
is a function of p.f............
an alternator operates at lagging power factor when over-
excited and operates at leading power factor when under-
excited.........bcoz at leading power factor......the rotor
ampere turn increases and hence flux increases, thereby
increasing the induced voltage......so to keep the induced
voltage constant.........the excitation has to be
decreased..........n vice versa

Answer / ashwani malhotra

The real power is goverened by Frequency of prime mover.
The relation between real power and frequency of prime
mover is inversly proportional.So as load increase on the
grid it is shared by the genset and increased load met by
reducing the speed .Then governer throat open more to enter
more steam to maintain the frequency.

The voltage at alternator is controlled by the reactive
power flow. So increase in excitation beyond normal provide
capacitive VARs and decrease in excitation less than normal
provides the Inductive VARs required by the system.
generally the system comprises of Inductive load like
motor,transformer so alternator operate mostly in Under
Excitation state.

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