Answer / sudhir purandare

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.

Answer / sanjay dalvi

IN INDIA, DG DESIGN FOR 0.8 POWER FACTOR,THEN IN UR MIND A
QUESTION MAY ARRISE WHY .8 ONLY??
ANSWER IS THE LOAD IS ALLWAYS INDUCTIVE IN NATURE SO WE
USED 0.8 PF IN DG DEGINING AS A LAGGING PF.
NOW COME TO OUR ACTUAL QUESTION

CONSIDER 1000 KVA DG SET WHICH DELIVER 800 KW O/P POWER

BUT IF IMPROVE POWER FACTOR FROM .8 TO 1 PF THEN
OBEIOUSLY POWER DELIVER INCREGES FROM 800 TO 1000KW

P= V*I*COS $ WE KNOW THAT PF IS 1
LOAD CURRENT IS ALSO SAME FOR
LOAD
HERE POWER INCREASE DIRECTLY EFFECT THE VOLTAGE LEVEL
IF THE VOLTAGE LEVEL GOES BEYOND THE LIMIT IT WILL TRIP
THE AVR SYSTEM OF DG & DG WILL STOP RUNNING

IF WE USE CAPACITOR BANK THEN VOLTAGE LEVEL INCREASE
BEYOND THE LIMIT..SO WE R NOT USEING CAPACITOR BANK.

Answer / ashish patil

sudhir answer is write. to avoid over loading we swiched
of capacitor bank.we dont control power factor through
exciter in case of DG.

Answer / anand

if we use the capacitor it affects thre DG set due to the
reactive power.....

Answer / kj

In a single DG the power factor is not a function of the
DG. It is a function of the load. Inductive loads will
produce a lagging power factor and capacitive loads will
produce a leading power factor.
If a capacitor bank is used and the PF on the DG becomes
too far leading the fact that the voltage rise leads the
current rise in the waveform causes induced currents to
flow in the rotor field. This induced current replaces the
current produced by the AVR. As the PF becomes more leading
the AVR does not produce voltage and control of the voltage
is lost. The voltage will rise above the nominal settings
if the PF becomes more leading after the AVR has shut down.

So although it is not normal practice to use capacity banks
with DG's, they can be used as long as the PF remains
lagging.

Answer / viswanath

we controlled the powerfactor though with exciter.that why
we not using the capacitor bank

Answer / tapan

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.

Answer / gopinath madikeri

dr frnds, what Sudhir has said is right.. dg sets are built
with AVR(automatic voltage regulators) as it controlls the
voltage & power factor according to the load there will be
no requirement of seperate capacitor bank.

Answer / mrinmoy boruah

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
location.
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.

Answer / sudhir purandare

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.

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