Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
40
CHAPTER 3
IMPROVEMENT OF LOAD POWER FACTOR USING FACTS
CONTROLLERS
3.1 INTRODUCTION
The low power factor effects on transmission line, switchgear, transformers etc. It is observed
that if the power plant works on low power factor, the capital cost of plant in generation,
transmission and distribution systems is increased. Higher the capital charges means, higher
the annual fixed charges, which will increase the cost per unit or the effect of all headed over
the consumer who has to pay more. Thus it is always an advantage for both the consumers and
the suppliers to work at higher power factors. Usually the suppliers encourage the people to
work at improved power factors by adopting a two part tariff, charging the consumer on his
maximum demand in kVA and the number of units consumed by him. The maximum demand
of the consumer is measured with a maximum demand meter, installed at consumer‟s premises;
the reading of meter is taken annually. If the consumers will try to work at low power factor,
for the same power from the mains, he will draw more current or his kVA demand is increased
for which he has to pay extra. This is how the consumer is discouraged to have low power
factors. The power factor is the ratio of active power component (kW) & apparent power
component (kVA) of any A.C. system.
B
kVA
kVAr

o
kW
Fig 3.1 Power Triangle
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
41
Referring Fig 3.1 Power triangle OAB, OA-represents active or real component of power
(kW).
OB- represents reactive or wattless components of power (kVAr) & AB-represents the
apparent power component (kVA). Basically power factor is defined as the cosine of power
triangle which must be right angled triangle. Therefore: from Fig 3.1
kW = kVA cos Φ
(3.1)
kVAr= kVA.sin Φ
(3.2)
kVAr = kW tan Φ
(3.3)
kVA= (kW)
cosΦ
(3.4)
The power factor will be of leading nature, if the current is leading the voltage, it will be of
lagging nature, if current is lagging the voltage and unity if current and voltage are in phase
with each other.[28]
3.2 FACTORS AFFECTING LOW POWER FACTOR
a) As most of the electrical applications are with induction motors, they work, on lagging
power factor of the power supplied.
b) The transformers at power stations, sub-station etc draw the magnetizing current which
causes the total current of the line to be lagging the line voltage
c) The industrial heating furnaces particularly induction heating will have very low
lagging power factor consuming system.
d) Arc lamps, fluorescent lamps, mercury vapour lamps etc. operate at lagging power
factor.
e) Transmission and distribution lines & feeders will also have more inductive effect,
hence main power flow through both the systems will be at low power factor.
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
42
3.3 EFFECT OF LOW POWER FACTOR ON POWER FLOW & POWER
CONSUMPTION
Let us consider an alternator delivering 1000 A at 500 V. (single phase).
Then its Rating = VI/1000 = 1000x500/ 100 = 500kVA
(3.5)
If the alternator is loaded at unity power factor, then the load supplied:
kVA x p.f = 500 x 1= 500 kW
(3.6)
If the load p.f is 0.6 lagging, then the power supplied by alternator is:
Load supplied = kVA x p.f = 500 x 0.6 = 300 kW At 0.6 p.f lagging
(3.7)
By the above computation, it is observed that alternator is developing its maximum current and
voltage even at 0.6 p.f lagging and supplying only 60% of its total capacity therefore in order
to supply its actual power say (500 kW) the alternator is to be over leaded and the conductors
connected between alternator and load must be provided with maximum cross-sectional area to
withstand the overload current. Hence for the given amount of power generation or
transmission, the size of alternator is bigger and large conductors are to be used for the power
transmission. In other words, greater will be the cost of generation and transmission. That is
the reason that the suppliers always stress the consumers to increase the power factor with their
utilities[28].
3.4 EFFECTS OF LOW POWER FACTOR ON TRANSMISSION LINES
 Effect on generators:
The generated kVA and kW capacities will have low power factor. Because of this, the power
supplied by the exciters is increased, copper losses in the generator winding are increased, and
so, the efficiency of generator is decreased.
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
43
 Effect on transmission lines :
For the transmission of power, more current has to be sent at low power factor. As the line has
to carry more current, its cross sectional area should have to be increased, which increases the
capital cost of the transmission line. Also increased current increases the line losses and
decreases the line efficiency. The line drop is also increased.
 Effect on transformers:
The transformers which are connected with transmission lines and with distribution feeders
will have the effect of decrease in kW capacity with the decrease in power factor also increase
in line voltage
 Effect on switchgear and bus bar
The cross-sectional area of bus bars, and the contact bars enlarged for the same amount of
power to be delivered at low power factors.
 Effects on prime movers
The generator will develop more reactive (kVAr) or wattles power with low power factor, but
certain amount of energy is needed to develop this power, which is being supplied by the prime
mover. This energy supplied by the prime mover is idle and represents as dead investment.
Working on low power factor decreases the efficiency of prime mover. [29]
3.5 BENEFITS OF POWER FACTOR IMPROVEMENT
The following are the benefits, listed with improved power factor.
i) The kW capacity of transformers and the lines is increased
ii) The efficiency of generating plant is increased
iii) The overall consuming cost per unit is decreased
iv) The regulation of transmission lines and distribution feeder is improved
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
44
v) The kW capacity of alternator is increased.
vi) The energy of the prime mover is better utilized.
3.6 METHOD OF IMPROVING POWER FACTOR
 By the use of static capacitors
The static capacitors are connected in parallel with the supply mains, which draw the current,
leading the voltage by 900 and neutralize the reactive lagging current component of the load
current, hence to improve the power factor nearest to unity.
 By the help of synchronous condenser
The synchronous condenser is also called as synchronous motor. This motor draws the current
from the mains at leading power factor, there by neutralizing lagging reactive component of
the load current. It also develops the mechanical power
 Phase advancer
These are the special commutator machines, which improve the power factor of induction
motors.
 FACTS controller
These are the powerful power electronics devices which are used to improve the power factor
of bulk or small quantity of power transmission and distribution lines [30]
 Reactive Current for the improvement of p.f
Considering an a.c. circuit with inductive load as shown in Fig. 3.2 and its vector diagram as in
Fig 3.3
I
Ir (Iµ)
K
Ic c
230V150 HZ
a.c. supply
r
L
Load
Fig 3.2 Circuit diagrams with inductive load
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
45
A
Reactive components
IsinΦ
Active components
IcosΦ
V

I
Fig 3.3 vector diagram to represent current components
Let the current supplied to the circuit is „I‟ Amp. and let this current is lagging the voltage by
an angle of Φ0. The current supplied to this circuit can be resolved into two components one
along the voltage vector and the other is in quadrature. The component along the voltage vector
is known as in phase vector or active component of current which is “I.cos Φ” and the other is
known as reactive component of current which is “-I sin Φ”. They are shown in Fig 3.3
In order to improve the power factor, angle „Φ‟should be decreased to zero for unity power
factor as cos Φ= cos.0 =1
In order to decrease the angle „Φ‟ the reactive component of current, I sin Φ is to be decreased.
This is obtained by introducing leading current, Ic through capacitor of magnitude equal to the
reactive component (I) in the circuit as in Fig 3.2 observed in Fig 3.3. This leading current, Ic
will lead the voltage exactly by 900 and will be in phase opposition to I the reactive inductive
component of current. Now Ic= +I sin Φ & I = -I sin Φ will neutralize each other leaving
supply current (I) in phase with V. Theory gives the power factor is unity. Thus the required
leading reactive current to compensate the existing lagging reactive current is given as
Ic = I [1-(p.f)2] [ 31]
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(3.8)
Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
46
3.7 POWER FACTOR IMPROVEMENT
By the method of introducing leading components of current in common component of current
is commonly employed. It is obtained by connecting a number of capacitors in parallel across
the main supply at the end. The value of the total capacitance required for improving the
power factor nearest to unity for a given power P, in the network at a frequency f and voltage
V is determined as follows
P= VI (p.f)
(3.9)
I = P
V(p.f)
(3.10)
C = P .tan Φ
2v2
(3.11)
It is observed from equation (3.11) that the capacitance required for improving the power
factor is inversely proportional to frequency „f‟ this shows that the static capacitors are best
suited for high frequencies also it is seen that the capacitance required is inversely proportional
to the square of the operating voltage. Thus the total value of the capacitance required per
phase in three phase system depends upon the nature of connections, whether star connected or
delta connected. In practice it is observed that the delta connection is preferable. A calculation
of capacitance of a capacitor to improve the power factor from 0.73 lagging to 0.93 lagging is
done.
3-ph supply
3-ph I.M
Star connected
Capacitor bank delta connected
Fig 3.4 Delta connected static capacitors bank
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
47
Motor & elements parameters
 Out put of I.M =400 hp
 Voltage (L-L) = 2000V
 Frequency of supply = 50 Hz
 Working p.f = 0.73 lagging
 Improved p.f = 0.93 lagging
 Capacitance of each capacitor = 57.47 µF
 Total number of capacitor in series = 4
 Each capacitor voltage = 500 V
 Frequency of supply = 50 Hz.
 Efficiency of motor = 85%
Motor line current with working p.f = IL1 = 142.8A
(3.12)
Ip1 = 99.96-J 101.98
(3.13)
Motor line current with required improved p.f = 0.93
IL2 = 107.43 A
(3.14)
Phase current (Ip2) =Ip2 = 99.91- J39.48
(3.15)
Reactive current to be neutralized = Iµ = Iµ1- Iµ2 = 62.56A
(3.16)
The bank of capacitors used to improve the power factor is connected in delta, therefore phase
voltage (Vph) = 2000V, but each unit of capacitors connected in series is as shown in Fig
3.4.The reactive current in each phase of the bank is
Iµp = 62.56 = 36.12 A
3
(3.17)
Let Xc be the capacitive reactance of each capacitor
Xc = 500 = 13.846
36.12
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(3.18)
Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
C = 229.95µF
48
(3.19)
Thus the capacitance of each capacitor of the bank is
[C =229.95 = 57.48µF]
(3.20)
4
Hence the capacitor bank of each capacitor must have 57.48µF capacitance to improve the p.f
from 0.73 lagging to 0.93 lagging. [32]
3.7.1 Improvement of p.f by FACTS Controller approach
98.1 kVA 62.89
D
ph
Is
Id
A
Ld
20.10 kVAr
98.1 kVA
58.5mH S C
229.95 F
Vph=115v
B
Booster converter
N
Single phase diode
bridge rectifier
Fig 3.5 FACTS Controller Circuit Diagram
Supply current (Is) = kVA = 98.1 x 1000 = 84.93A
Vp
1155
(3.21)
Thus Rating of rectifier = Vp Ip/1000=S = 98.1 kVA.
(3.22)
Diode or Inductor current (Id) =Rectifier Rating = Id = 62.89A
1.35x Vp
Peak current (Ipk) = Form factor x Id = Ipk = 69.81A
(3.23)
Voltage across diode & inductor (Vd) = Vph = Vd = 816.71V
(3.25)
Inductance of inductor (Ld) = Vd = 58.5mH
4fIpk
(3.26)
Switching rating = rectifier rating = 98.1 kVA.
(3.27)
Capacitor rating Data In2 = (38.11) 2, ωn = 2π50 = 314.16 rad/sec
(3.28)
(3.24)
2
Where In = 1.55x kVAr/Vd = 38.11A
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
49
C = 229.95 µF
(3.29)
Therefore capacitor rating = In2 = Q = 20.10 kVAr
2fc
B
(3.30)
S=98.1 kVA
Q=20.1 kVAr

o
P
A
Fig 3.6 Power Triangle for FACTS
sin Ф = kVar = 20.10 = 0.20
kVr
98.10
(3.31)
Ф = sin-1 (0.20) = 11.530
(3.32)
p.f = cos Ф = cos (11.530) = 0.98 [33]
(3.33)
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
50
3.8 SIMULATION RESULTS
continuous
power
current 1
Voltage
measurement
model
V
I
PQ
current 2
current
Active &
Reactive power
Fig 3.7 Simulation diagram for improvement of Power Factor
0.6283
Display
1
V
magnitude
signal
angle
V_fundamental
X
X
k-
I/2
Gain
cos
Deg->Rad
magnitude
2
I
signal
angle
sin
X
I_fundamental
Fig 3.8 Circuit Diagram with Inductive load
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1
PQ
Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
51
Fig 3.9 Input current waveform for Inductive Load
(Time on x-axis, Current on y-axis)
Fig 3.10 Real and Reactive power waveforms
(Yellow colour line = Q, Purple colour line=P)
(Time on x-axis, P-Q on y-axis)
0.7333
Magnitude
1
V
Display
X
Signal
X
angle
V_fundamental
+
-
K-
cos
Deg->Rad
Magnitude
2
I
Signal
angle
I/2
Gain
-0.6799
sin
X
Display 1
I_fundamental
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1
PQ
Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
52
Fig 3.11 Simulated diagram of Delta connected static capacitors bank
Fig 3.12 Waveform of Improved active & reactive power quality response
(Yellow colour line = Q, Purple colour line=P)
(Time on x-axis, P-Q on y-axis)
100mH
Current
measurement
D5
D1
D3
V
PQ
I
Vo
200µF
Active &
Reactive
power
D6
120V
60Hz
T
100VA
120V/24V
Vd1 Vd2
D2
D2&D4;
Circuit
D4
Scope1
Max
Fig 3.13 Simulated diagram of FACTS (UPFC)-Single phase rectifier
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Scope2
Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
53
[1.1 4e+007]
Display
1
Vabc
P
X
1
2
PQ
Iabc
+
-
1.16 4e+007
+
-
Display1
+
-
1/sqrt(3)
X
Fig 3.14 Simulated diagram of FACTS Controller Approach (RP/AP= tan Ф)
The Fig 3.14 computes the 3-ph instantaneous real power and reactive power using
the following equations:
1) P=Va1la+Vb1lb+Vc1lc
2) Q=1/sqrt(3) (Vbc1la+Vca1lb+Vab1lc)
Note: Equation-2 is valid only for a balanced & harmonics-free system.
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
54
Fig 3.15 Real & Reactive power waveform of UPFC with Max. p.f
(Yellow colour line = Q, Purple colour line=P)
(Time on x-axis, P-Q on y-axis)
Fig 3.16 Output waveform of diode rectifier voltage with FACTS controllers
(Time on x-axis, Vdc on y-axis)
3.9 CONCLUSION
In this work the power factor is computed by static capacitors approach and FACTS controllers
approach theoretically & verified the results by simulation. The simulation results are noted. In
comparison, it is found that the FACTS controller approach is better than the static capacitor
approach for power factor correction. Hence the FACTS controllers methods can be
implemented for the power factor improvement in both transmission & distribution lines
effectively. The comparative evaluated results of power factor are tabulated in Table 3.1
Table 3.1 Evaluation of Power factor
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Chapter 3
Improvement of Load Power Factor Using FACTS Controllers
S.No Name of the circuit
Power factor
1
Inductive load
0.73
2
Induction motor with C- bank
0.93
3
Using FACTS (UPFC controller)
0.98
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55