DG set is a power source. Capacitor bank is required for a
load to maintain the power factor i.e. reactive power. The
alternators are designed for 0.8 pf. if the load pf is lower
than this value, it will overload alternator. under such
conditions it is necessary to install a capacitor bank.
If Dg set is running parallel with grid we can adjust the
power factor through excitation, but if it is running in
ideal mode we cant adjust the power factor through
excitation, so we need capacitor bank at that time.
Basically the alternators are designed for 0.8 pF
only.Accrodingly the excitor voltage and current is
designed. You can not adjust the excitor voltage and
current to meet the power factor of load. This will
overload the alternator.
My dear frnds ,when DG set running ideal mode there is AVR
(Automatic Voltage Regulator)wich maintaine its voltage &
power factor according to load.So i think there don't want
any other capacitor bank.
DG set supplies necessary current to load. Its (internal)
Power Factor is governed by its design. DG sets like
transformers are rated in KVA i.e. KVxI.
Whatever be the load power factor, a DG set's internal power
factor will be governed by its design.
If a reactive load such as inductor or capacitor of
equivalent capacity (LOAD KVA = DG set's KVA)) is connected
across a DG set's terminals, the power factor measured at
these terminals will be nearly 0. However in this situation
also DG set's internal PF wikk be its designed PF.
Power factor is a parameter with respect to its measurement
If load supplied by a DG set consists of large number of low
power factor loads which eats up only very small portion of
its total capacity and the balance load is taken by a high
power factor load, then the power factor at DG set's
terminal will still be high. But the DG set's internal power
factor will still be governed by its design.
in case of generating stations,where few critical loads
need to be made ON ,DG set by its own capacity can supply
current n voltage to load but in case of distribution
substation where in case load requirement is not met by DG
alone ,we require capacitor banks also.
Increasing p.f shall automatically enhance the Kw demand
then its designed value and the alternator shall not be
able to cater this additional Kw and shall trip due to over
current. Hence it is not recommended to install the
capacitors accross the DG set to increase its p.f more then
its designed value.