Tariff Powerfactor Supplysystem MechProperties ElecProperties Transmission UGCable DCDistribution ACDistribution
POWER FACTOR IMPROVEMENT
Q. Define power factor .
A. The cosine of the angle between the voltage and current of an ac
circuit is known as power factor for that circuit .
Q. Write different
formula for the power factor .
A. Cosø = active power ( KW )/
apparent power(KVA)
= r/z
Q. What you meant by
0.6 lagging ?
A. This means that the power
factor of a load is 0.6 where current lags the voltage by an angle equal to Cos
-1 (0.6) .
Q. Write down the
relation between different powers .
A. (apparent power)2 = (active power)2 + (reactive power)2 .
Q. What is the
equation of reactive and apparent power and their unit ?
A. Reactive power = V*I*sinø =
kw*tanø
Unit kvar
Apparent power = V*I =
kw/cosø
Unit kva
Q. What is the power
equation for 3-phase and 1-phase system ?
A. P = 3*V*I*cosø (for 3-phase
)
P = V*I*cosø ( for 1-phase
)
Q. Why electrical
machines are rated in KVA ?
A. Because at the time of
manufacturing of electrical equipment the power factor of the load is unknown
.
Q. What is the effect
of power factor on the voltage regulation ?
A. At low power factor for
lagging load the load current is large which causes more voltage drops in electrical
equipments , transmission and distribution lines . So the receiving end voltage
decreases and causes voltage fluctuation .
Q. Write the name of
different equipments used for power factor improvement ?
A. Static capacitor
Synchronous condenser
Phase advancers
Q. What is the value
of pf on a large generating station ?
A. 0.8 to 0.9
Q. What is
synchronous condenser ?
A. A synchronous motor when running at no load
and over excited condition , it takes leading current from the supply. At this
condition that synchronous motor is called synchronous condenser .
Q. How you meet the
increased kw demand ?
A. There are two process
By increasing the kva
capacity at the same power factor .
By improving the power
factor at same kva .
Q. Power factor
improvement means _________ .
A. Increasing the value of power
factor or decreasing the power factor angle .
Q. ________the power
factor of the generating station _____________is the kwh it delivers to the system .
A. Greater , higher
Q. I*cos ø always is
in _________with v .
A. Phase
Q. The angle between
the I*sin ø and V is __________.
A. 900
Q. Lower the value of
power factor _________the kva rating of equipment .
A. Greater
Q. The electrical
equipments are rated in ________ .
A. KVA
Q. If power factor
increases the load current _________ .
A. Decreases
Q. For carrying the
current at constant voltage and power the conductor size is __________for low power factor .
A. Large
Q. Arc lamps operate
at _________ power factor .
A. Low lagging
Q. The maximum value
of power factor is_________ .
A. (unity) 1
Q. Pf correction
equipments are connected in__________with electrical equipment .
A. Parallel
Q. The reactive power
taken by a synchronous motor depends on ___________ and__________.
A. Dc field excitation ,
mechanical load
