Transcript role of capacitor in distribution system

Power Distribution System
Power Factor Improvement
BY
INSTALLING CAPACITORS ON
DISTRIBUTION SYSTEM
Prof. Dr. Suhail Aftab Qureshi
1
WHAT IS POWER FACTOR?
Power Factor is the ratio of ACTIVE
POWER to the TOTAL POWER (apparent
power):
Power Factor
=
Active Power
Total Power
=
P
S
S
=
Total power of Generator (or used)
P
=
Power consumed in the load (active power)
Q
=
Reactive power stored in magnetic field. Or
wasted power
2
WHAT IS POWER FACTOR?
Vectorial Representation:
S
P.Q
Φ
Load
P
j=90o
S
Q
Generator
Total power = S = VI
= (units = KVA)
Active power = P = VI CosΦ = (units = KW)
Reactive power= Q = VI SinΦ = (units = KVAR)
V = Voltage : Volts
I = Current : Ampere
Φ = Physical displacement of V&I
Power Factor = CosΦ
V
Φ
I
3
WHAT IS LOW POWER FACTOR?
P
P.F. = S
If the ratio of active power (P) to total power
(S) is less than one (unity) then the power
factor is low, which means total power is not
being consumed.
Example:
S = 100KVA
Generator
P = 80KW
S = 100KVA
Generator
P = 100KW
P.F = 0.8
P.F = 1.0
Q = 60-KVAR
Q =
0
4
WHAT IS LOW POWER FACTOR?
The above example clearly indicates that
a generator of total power of 100-KVA will
supply maximum of 80-KW of active
power to a load with P.F. = 0.8 and the
same generator will supply maximum of
100-KW of active power to load with P.F
= 1.0.
5
HOW TO IMPROVE THE
POWER FACTOR ?
The power factor can be improved by
supplying KVAR to the loads (inductive type)
“Capacitor is source of KVARs”
Therefore the power factor of connected load
can be improved by installing power factor
improvement capacitors/capacitor banks
6
HOW TO IMPROVE THE
POWER FACTOR ?
LOAD
LOW POWER FACTOR
CAPACITOR
LOAD
IMPROVED POWER FACTOR
Fig.I
7
KVA AND KW SAVING
P(KW)
Φ2
Φ1
S(K
VA)
2
Q(KVAR)2
S(
KV
A)
Q(KVAR)1
1
COSΦ2 = 0.9
Q(KVAR)C
KVA (Saving) = S(KVA)1 – S(KVA)2
Vectorial representation of P.F Improvement. 1&2
refer to before and after improvement of P.F.
8
KVA AND KW SAVING
P2
P1
Φ2
Φ1
S
KVA
COSΦ2 = 0.9
KW (Saving) = P1 – P2
9
POWER FACTOR IMPROVEMENT
BY CAPACITOR BANK
WAPDA
CONSUMER
KWh KVARh
KW
KVAR
KW
KVAR
METERS
WAPDA
LOAD
CONSUMER
KWh KVARh
KW
KW
KVAR
LOAD
METERS
Power Factor Improvement
by Installation of Capacitor
CAPACITOR
10
DISADVATAGES OF LOW
POWER FACTOR
1. For a given power to be supplied, the current
is increased.
2. The current thus increased in-return causes
increase in copper losses (PL=I2R) and
decrease in the efficiency of both apparatus
and the supply system, which results in
overloading and hence burning of the
associated equipment.
11
DISADVATAGES OF LOW
POWER FACTOR
3. Copper losses in transformers also increases.
4. Generators, transformers, switches, transmission
lines and other associated switchgear becomes
over-loaded.
5. Voltage regulation of generators, transformers
and transmission lines increases.
6. Hence, cost of generation, transmission and
distribution increases.
12
NATURAL POWER FACTORS
o
CEILING FAN
0.5 TO 0.7
o
CABIN FAN
0.5 TO 0.6
o
EXAUST FAN
0.6 TO 0.7
o
SEWING MACHINE
0.6 TO 0.7
o
WASHING MACHINE
0.6 TO 0.7
o
RADIO
0.9
o
VACUUM CLEANER
0.6 TO 0.7
o
TUBE LIGHT
0.5 TO 0.9
o
CLOCK
0.9
o
ELECTRONIC EQUIPMENT
0.4 TO 0.95
13
NATURAL POWER FACTORS
o
NEON SIGN
0.5 TO 0.55
o
WINDOW TYPE AIR CONDITIONER
0.62 TO 0.85
o
HAIR DRYERS
0.7 TO 0.8
o
LIQUIDISER
0.8
o
MIXER
0.8
o
COFFEE GRINDER
0.75
o
REFRIGERATOR
0.65
o
FREEZER
0.7
o
SHAVER
0.6
o
TABLE FAN
0.5 TO 0.6
14
NATURAL POWER FACTORS
o
MERCURY VAPOUR LAMP
o
INDUSTRIAL INDUCTION MOTOR:
O.4 TO 0.6
◘
NO LOAD
O.18
◘
25% FULL LOAD
0.56
◘
75% FULL LOAD
0.81
◘
100% FULL LOAD
0.85
◘
125% FULL LOAD
0.86
o
COLD STORAGE
O.76 TO 0.80
o
CINEMAS
0.78 TO 0.80
o
METAL PRESSING
O.57 TO 0.72
15
NATURAL POWER FACTORS
o
OIL MILLS
O.51 TO 0.59
o
WOOLEN MILLS
O.70
o
POTTERIES
0.61
o
CIGARETTE MANUFACTURING
0.80
o
FOUNDRIES
0.59
o
STRUCTURAL ENGINEERING
0.53 TO 0.68
o
CHEMICALS
0.72 TO 0.87
o
MUNICIPAL PUMPING STATIONS
0.65 TO 0.75
o
OIL TERMINALS
0.64 TO 0.83
o
ROLLING MILLS
0.60 TO 0.72
16
NATURAL POWER FACTORS
o
PLASTIC MOLDING
0.57 TO 0.73
o
FILM STUDIOS
O.65 TO 0.74
o
HEAVY ENGINEERING WORK
0.48 TO 0.75
o
RUBBER EXTRUSION AND MOLDING 0.48
o
PHARMACEUTICALS
0.75 TO 0.86
o
OIL AND PAINT MANUFACTURING
0.51 TO 0.69
o
BISCUIT FACTORY
0.60
o
LAUNDRIES
0.92
o
FLOUR MILLS
0.61
o
GLASS WORKS
0.87
17
NATURAL POWER FACTORS
o
IRRIGATIONS PUMPS
O.62 TO 0.80
o
REPAIR SHOP, AUTOMATIC LATHE, 0.6
WORKSHOP, SPINNING MILLS,
WEAVING MILL
o
WELDING SHOP
0.5 TO 0.6
o
HEAT TREATMENT SHOP, STEEL
0.65 TO 0.8
WORKS, ROLLING MILLS
o
TEXTILE
0.65 TO 0.75
o
CEMENT
0.8 TO 0.85
o
OFFICE BUILDING
O.8 TO 0.85
18
ADVANTAGES OF POWER
FACTOR IMPROVEMENT
PFI Capacitor’s addition, thus can be viewed in two lights.
i. Adding capacitor, releases circuit capacity for
more load or relieves the overloaded circuit. The
capacitor KVAR per KVA of load increase is of
particular interest as this establishes the average
cost of supplying each additional KVA of load.
This cost can be compared with the cost per KVA
of increasing the transformer or supply circuit
rating and would justify the application of
capacitors.
19
ADVANTAGES OF POWER
FACTOR IMPROVEMENT
ii. Capacitors applied to given load reduce the I2R
losses in the supply circuit. For a 70 percent power
factor load with 40-KVAR of capacitors added for
each 100 KVA of circuit capacity, the I2R loss will
be 59% of its former value. The losses are not only
reduced in the circuit in which the capacitors are
applied but in all the circuit back to and including
the source generator.
20
ADVANTAGES OF POWER
FACTOR IMPROVEMENT
Automatic Power Factor improvement capacitors or
capacitor banks applied on the load end of circuit,
with lagging power factor (more than 95% loads),
have particular effects, one or more of which may be
the reason for the application.
1. Improves the power factor at the source.
2. Reduces system losses as current in
conductors decreases.
21
ADVANTAGES OF POWER
FACTOR IMPROVEMENT
3. Improves voltage level at the load.
4. Decreases KVA loading on the source.
5. Reduces investment in system facilities per
KW of load supplied.
6. Eliminates low power factor penalty imposed
by WAPDA.
22
ROLE
ROLE OF
OF CAPACITOR
CAPACITOR IN
IN DISTRIBUTION
DISTRIBUTION SYSTEM
SYSTEM
Disadvantages of Low Power Factors.
The disadvantages of low power factor are summarized below:In transmission/distribution lines, it is only in phase component of
line current, which is active in the transmission of power. When P.F
is low, then in phase (active) component is small but the reactive
component is large, hence unnecessarily large current is required
to transmit a given amount of power. Large reactive component
means, large voltage drop, and hence greater Cu-losses with the
results that regulation is increased and efficiency is decreased.
Supply authorities usually bound to maintain the voltage at
consumer’s terminal within prescribed limits, for which they have to
incur additional capital cost of tap changing gear on transformers to
compensate for the voltage drop. Hence the supply authorities
penalize the industrial consumers for their low P.F by charging
increased tariff for KVA maximum demand in addition to useful KW
charge. Obviously it is advantageous for the consumer to improve
his load P.F.
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ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
How to Improve the Power Factor.
Power factor can be improved by supplying KVAR to the Inductive
load. Different techniques to improve the P.F are given below:

With Synchronous Motors
With Capacitors
Synchronous motors are not commonly used in distribution
network for P.F improvement because it requires regular
maintenance & also expensive. This method is mostly used to raise
P.F of system having large Induction Motor loads. Also it is difficult
to install at
In distribution system, Capacitors are the most common method
for power factor correction as it is the least expensive & almost
maintenance free.
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OFCAPACITOR
CAPACITORIN
INDISTRIBUTION
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SYSTEM
Power Factor Correction with Capacitors.
Capacitor is a source of KVARs i.e it provides a static source of
leading reactive current. It is desirable to add capacitors in the load
areas supplying the lagging component of the current. There are two
types of Capacitors according to their mode of installation.
i.
ii.
Series Capacitors
Shunt Capacitors
Series Capacitors have some draw backs because all load current
will flow through capacitors, so if the load is more then we need big
capacitor, further it boost the voltage at the point of installation.
Shunt Capacitors are more suitable for installation on distribution
feeder as it produce a uniform voltage boost per unit of length of line,
out of its point of installation. Therefore, it should be installed as far
out on distribution system as practical, close to the loads requiring the
KVARs.Shunt Capacitor can be viewed in two lights. Adding
Capacitors releases circuit capacity for more load, and adding
capacitors relieve over loaded circuits.
25
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Power Factor Correction with Capacitors.
There are two types of Shunt Capacitors.
i.Switched
Capacitors
ii.Fixed Capacitors
Switched Capacitor
Switched Capacitors banks are programmable capacitors & can be
switched on/off during load cycles by different program settings.Time
Clocks, temperature, voltage, current and kilovars controls are
common actuators for capacitor switching.
Switched Capacitors are usually applied to correct the power factor
to 0.97 at peak load (if economical). Each Switched Capacitor bank
should save at least 8 KW loss at peak load.
26
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Power Factor Correction with Capacitors.
Fixed Capacitors
Fixed Capacitor bank are usually applied to correct the power factor
to unity at light load (if economical) & permanently connected into
the system through fuses.
Proposed permanently connected capacitor application should be
checked to make sure that the voltage to some consumers will not
rise too high during light load periods.
Each Fixed capacitor bank should save at least 1 KW loss at light
load.
These are quite cheap as compared to switched capacitors,
therefore, they are often used in distribution network to improve the
power factor.
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OFCAPACITOR
CAPACITORIN
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Benefits to Be Achieved by Installing
Shunt Capacitors on Power Distribution
System.
Reactive Power Compensation i.e decrease KVA
loading on source, therefore, additional KW
loading may be placed without augmenting the
existing system.
Power Factor Improvement
Reduction in Line Current i.e reduce lagging
component of circuit current.
Reduction in System Losses i.e reduce I2 R power
loss & I2X Kilovar losses in the system.
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OFCAPACITOR
CAPACITORIN
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Benefits to Be Achieved by Installing Shunt
Capacitors on Power Distribution System.
Reduction in Voltage Drop i.e increase voltage level
at the load.
Reduce Investment in System Facilities per KW of
Load Supplied.
Advantage No.1 is a direct consequence of installing
a shunt capacitor because the same supplies the
reactive demand to the load, relieving extra burden
to reactive power. Thus due to reactive power
compensation all other advantages are automatically
29
achieved.
ROLE
ROLE OF
OF CAPACITOR
CAPACITOR IN
IN DISTRIBUTION
DISTRIBUTION SYSTEM
SYSTEM
Power Factor Improvement By Capacitor Bank
Before Installation of Capacitor
Meters
Kwh
Kvarh
KW
KW
Load
G/Station
KVAR
After Installation of Capacitor
KW
KVAR
Meters
Kvarh
Kwh
KW
Load
KVAR
G/Station
KW
KVAR
Capacitor
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Some Examples which Illustrate the Benefits to be Achieved By
Installing Capacitors.
i.
Reactive Power Compensation i.e Decrease in KVA Loading at
Source.
Assume that a single phase load supplied from a single phase A.C
System with supply voltage as 230 Volts has active & reactive power
demand as 3000 Watts and 4000 Vars respectively. If we install a
shunt capacitors of rating 3000 Vars on the load point, then reactive
power equal to 3000 Vars is compensated and directly supplied by the
capacitor, leaving behind only 1000 Vars on the system. The Effect is
shown by the following calculations.
VA burden on the System before installation of Capacitors =
( 3000² + 4000²)1/2 = 5000 VA
VA burden on the System after installation of Capacitors =
(3000² + 1000²)1/2 = 3162 VA
It means that VA burden on the system has been largely reduced due
31
to reactive power compensation.
ROLE
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OFCAPACITOR
CAPACITORIN
INDISTRIBUTION
DISTRIBUTION SYSTEM
SYSTEM
Some Examples which Illustrate the Benefits to be Achieved By Installing
Capacitors.
i.
Reactive Power Compensation i.e Decrease in KVA Loading at Source.
Assume 100 KVA Circuit or piece of apparatus has to carry 100 KVA at various
P.F.
60%
70%
80% Load P.F
90%
0
20
40
60
80
CAP. Kvar in % of Circuit KVA
100
32
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Some Examples Illustrating the Benefits to be Achieved By Installing
Capacitors.
Power Factor Improvement
ii.
This advantage is obtained as a consequence of reactive power
compensation.
From the example discussed in (i) above we can conclude as under:
Power Factor before installation of a shunt capacitor = W = 3000 = 0.6
VA 5000

Power Factor after installation of a shunt capacitor = W = 3000 = 0.949
VA1 3162
It means power factor has been improved from 0.6 to 0.949.
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ROLEOF
OFCAPACITOR
CAPACITORIN
INDISTRIBUTION
DISTRIBUTION SYSTEM
SYSTEM
Some Examples which Illustrate the Benefits to be Achieved By Installing
Capacitors.
ii.
Power Factor Improvement.
Assume 100 KVA Circuit or piece of apparatus has to carry 100 KVA at various
P.F.
90%
80%
70%
60% Load P.F
0
20
40
60
80
100
CAP. Kvar in % of Circuit KVA
34
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Some Examples Illustrating the Benefits to be
Achieved By Installing Capacitors.
Reduction in Line Current
iii.
As the reactive power compensation causes reduction in VA burden
of the line, so for a system having regulated supply voltage, it can be
seen that reactive compensation actually causes reduction in line
current.
From the data of (i) the values can be calculated as under:
VA before installing capacitor was = 5000, V = 230 Volts

VA = V x I,

VA after installing capacitor was = 3162,

VA1 = V x I1
Therefore I = (VA/V) = (5000/230) = 21.7 Amps
V = 230 Volts
Therefore I1 = (VA1/V) = (3162/230) = 13.7 Amps
It means that current has been reduced from 21.7 Amps to 13.7
Amps.
35
ROLE
OF CAPACITOR
ROLE OF
CAPACITOR IN
IN DISTRIBUTION
DISTRIBUTION SYSTEM
SYSTEM
Some Examples Illustrating the
Achieved By Installing Capacitors.
Benefits
to
be
Reduction of System Losses
iv.
Assume that power was supplied through 800 ft. long S/Phase L.T line
of Gnat conductor having resistance per mile as 2.11 ohms and
capacitor has been installed. The losses can be calculated as under:
Resistance R = (2.11 x 800)/5280 = 0.32 ohms

System Losses for one year = 2 (VA)² x0.32 x8760 =2 (5000)²x 0.32 x 8760
without Capacitor
(V)²
[ 1 mile = 5280 ft.]
(230)²
= 2649527 Watt hours

System Losses for one year with capacitor

=2(3162)²x0.32x8760/(230X230)=


1059625 Watt hours
%age Reduction in System Losses = (2649527
36
– 1059625 )x 100/2649527 = 60%
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Some Examples Illustrating the Benefits to be Achieved By
Installing Capacitors.
Reduction in Voltage Drop
v.
Voltage Drop before and after installing shunt capacitor can be calculated by
using the following formulas.

V.D = (R x W) + (Xl x VAR)
OR
V.D = Ir R + Ix X
Without Capacitor
V

V.D = (R x W) + (Xl x VAR1) OR
V.D = Ir R + Ix X – IcX With Capacitor
V
Suppose
R = 0.64 ohm for S/P circuit Xl = 0.145 ohm for S/P circuit, V = 230 Volts
W = 3000 Watt,
VAR = 4000 Vars,
VAR1=1000 Vars

V.D = (0.64 x 3000) + (0.145 x 4000) = 10.86
Volts Without Capacitor
230

V.D = (0.64 x 3000) + (0.145 x 1000) = 8.97 Volts
With Capacitor
230
Reduction in Voltage Drop = 10.86 – 8.97 = 1.89 Volts
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ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Vectorial Representation of Power Factor
Improvement
P (KW)
After improving P.F from ø1 to ø2,
KVAR is reduced from Q1 to Q2. The
difference in values of KVAR is due to
capacitor, which supply leading
KVAR (Qc) to partially neutralize the
lagging KVAR of the System.
ø1
ø2
Q2 (KVAR)
Q1 (KVAR)
Leading KVAR Supplied by Capacitor is Qc = Q1 – Q2
Qc (KVAR)
Qc = P (tan ø1 – tan ø2)
Before Capacitor Installation
After Capacitor Installation
ø1= Power Factor before Improvement
ø2= Power Factor After Improvement
P = Active Power (KW) at ø1
P = Active Power (KW) at ø2
S1 = Apparent Power (KVA) at P.F ø1
S2 = Apparent Power (KVA) at P.F ø2
Q1= Reactive Power (KVAR) at at P.F ø1
Q2= Reactive Power (KVAR) at at P.F ø238
ROLE
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OFCAPACITOR
CAPACITORIN
INDISTRIBUTION
DISTRIBUTIONSYSTEM
SYSTEM
Effect of Shunt Capacitors on Feeder Voltage Profile
The effect of shunt capacitor application on voltage profile of
Feeder, where the load is assumed to be uniformly distributed
along the Feeder is illustrated in figure as below.
Sub Station
Uniformly distributed Load
Capacitor
Rise produced
by Capacitor
Volts
Sub Station
Reference
Distance
Voltage Profile of Feeder With & Without Capacitor
Feeder Profile
with Capacitor
Feeder Profile
without Capacitor
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ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Effect of Shunt Capacitors on Feeder Voltage Profile

Capacitors produces a voltage rise because of its leading
picofarad current flowing through the inductive reactance of
the feeder.

As is seen in the figure, this voltage rise increases linearly
from zero at sub station to its maximum value at the
capacitor location.

Between the capacitor location & the remote end of the
feeder, the rise due to capacitor is at its maximum value.

When the capacitor voltage-rise profile is combined with
original feeder profile, the resulting net profile is obtained.

The capacitor has increased the voltage level all along the
40
feeder, resulting also in reduced voltage spread..
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Effect of Shunt Capacitors on Feeder
Voltage Profile
Proposed permanently connected capacitors
should be checked to make sure that voltage to
some customers will rise too high during light load
periods.
Switched capacitor application should be checked
to determine that switching the capacitor bank on
or off will not cause objectionable voltage flicker.
41
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ROLE OF
OF CAPACITOR
CAPACITOR IN
IN DISTRIBUTION
DISTRIBUTION SYSTEM
SYSTEM
Effect of Series Capacitor on Feeder Voltage Profile
The effect of series capacitor application on voltage profile of
Feeder, where the load is assumed to be uniformly distributed along
the Feeder is illustrated in figure as below.
Sub Station
Uniformly distributed Load
Series Capacitor
Rise produced
by Series Cap
Volts
Sub Station
Reference
Distance
Feeder Profile
with series Cap
Feeder Profile
without Series Cap
• The series capacitor produces no voltage effect between the source & the
capacitor location and its entire boost effect is between the capacitor location
and the remote end of the feeder.
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ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Effect of Voltage Regulator on Feeder Voltage Profile
The effect of feeder voltage regulator is shown in figure below
Sub Station
Uniformly distributed Load
Voltage Regulator
Rise produced
by regulator
Volts
Sub Station
Reference
Distance
Feeder Profile
with regulator
Feeder Profile
without regulator
• Like series capacitor, voltage regulator produces no voltage effect between the
source & the regulator location and its entire boost effect is between the
regulator location and the remote end of the feeder.
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OFCAPACITOR
CAPACITORIN
INDISTRIBUTION
DISTRIBUTIONSYSTEM
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Common Methods of Connecting Capacitors
Most common methods of connecting capacitors are as under:3-Phase Grounded Wye
3-Phase Ungrounded Wye
3-Phase Delta
Single Phase
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ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Common Methods for Connecting Capacitors
Fuse
Gnd
Grounded wye
Ungrounded wye
Delta
S/P Ground to
Neutral
Grounded Wye & Ungrounded Wye connections are usually made
on high voltage circuits, whereas delta & single phase connections
are usually made on low voltage circuits.
Majority of Capacitor equipment installed on distribution feeders is
connected grounded wye.
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ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Common Methods for Connecting Capacitors
Grounded wye connection has number of advantages & benefits
over Ungrounded wye connection.
With grounded wye connection, capacitor tanks/frames are at ground
potential. This provides increased personnel safety.
Grounded wye connections provides for faster operation of the series
fuse in case of a capacitor failure.
Grounded capacitors can bypass some line surges to ground and
therefore exhibit a certain degree of self-protection from transient
voltages & lightning surges.
The grounded wye connection also provides a low impedance path
for harmonics.
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ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Common Methods for Connecting Capacitors
If the capacitors are electrically connected ungrounded wye, the
maximum fault current would be limited to three times line
current. If too much fault is available, generally 5000 A, the use of
current limiting fuses must be considered.
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How Many Capacitors to Install
The number of capacitors to install to raise the power factor from
one value to another can be computed by using Stander Table.
48
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
ROLE OF CAPACITOR IN DISTRIBUTION
SYSTEM
How Many Capacitors to Install
49
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
How Many Capacitors to Install
50
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
How to Select a Location Of Capacitor to be Installed
The application of shunt capacitor to a distribution feeder produces a
uniform voltage boost per unit length of line, out to its point of
application. Therefore it should be installed as far out on distribution
system as practical, close to load requiring the Kvars.
Many Factors influence the location of Capacitor such as the circuits in
plant, the length of the circuits, the variation in load, the load factor,
type of motors, distribution of loads, constancy of load distribution.
The maximum loss reduction on a feeder with distributed load is
obtained by locating capacitor banks on the feeder where the
capacitor kilovars is equal to twice the load kilovars. This principle
holds whether one or more than one capacitor bank is applied to a
feeder.
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ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Protection Principles
There are several major factors which must be considered during
the design phase of a power factor correction capacitor
application.
i.
Fundamental Protection Principles

Safety of all personal who are required to work near or with
the equipment should be of prime importance.

Capacitors should be connected to system through fuses
so that a capacitor failure will not jeopardize system
reliability or result in violent case rupture.

To assure that the proper fuse protection is provided, the
installed capacitor fuse ratings are listed in standard Tables.
52
ROLE
ROLE OF
OF CAPACITOR
CAPACITOR IN
IN DISTRIBUTION
DISTRIBUTION SYSTEM
SYSTEM
Protection Principles
ii.
Capacitor Tank Rupture
•
Capacitor tank rupture will occur if the total energy applied to
capacitor under failure conditions is greater than the ability of
the capacitor tank to withstand such energy.
•
Tank rupture curves are essential for correct selection of fuse
link for over current protection of any capacitor installation.
•
Fuse selection should be based upon the coordination of the
fuse link maximum clearing curve and the high voltage
capacitor tank rupture curve
53
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Protection Principles
iii.
•
iv.
•
•
Ventilation
Although very efficient power capacitors do consume power and
generate heat. This heat must be adequately ventilated when
enclosed or exposed to higher than normal ambient
temperature.
System Voltage
Capacitors are designed for operation on 50 or 60 Hz sine wave
power lines at a specific voltage, which is mentioned on the unit
name plate.
However, they are normally designed to operate at over
voltages of 10% without damage to the capacitor. The Kvar
output of the capacitor increases as square of the applied
voltage.
KvarE2 = Kvar (E2)²
(E1)²
54
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Protection Principles
iv.
System Voltage

For example 450 Kvar, 11 KV capacitor will supply 492 Kvar at 11.5 KV.
KvarE2
=
KvarE2
=
450 (11500)²
(11000)²
492
55
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Protection Principles
v.
Harmonics Distortion
•
Capacitors are designed to operate on sine wave current with
limited amount of harmonics.
•
Typical applications that may cause harmonics current
problems are arc furnaces, saturable reactors, rectifies and
solid state motor controls.
•
Capacitors are usually designed to operate 135% of rated
Kvar. This includes any increase due to over voltage as well
as that due to harmonic currents.
•
The total rrms current equal to
where n = harmonic number
(I60)2 + (I2)2 + (I3)2 + ------+ (In)2
56
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Protection Principles
vi.
Discharge Resistor
•
When the line voltage is removed from a power capacitor, the
danger exists that, even days later, under certain conditions, the
unit would retain extremely high charge.
•
To eliminate this hazard, all power capacitors contain internal
discharge resistors. This resistor assembly will reduce the
terminal voltage from line voltage to 50 V within 5 minutes of deenergization for capacitor rated higher than 1200 V ac and within
1 minute for capacitors rated less than 1200 V ac.
vii.
High Frequency Charging Current
•
High frequency charging currents can result in blown fuses.
•
The use of series reactors & special switches are sometimes
required to reduce these currents to safe levels.
•
Proper installation of lightening arresters will ensure the
57
protection of capacitor equipment from lightning surges.
ROLE
ROLEOF
OFCAPACITOR
CAPACITORIN
INDISTRIBUTION
DISTRIBUTION SYSTEM
SYSTEM
Example of Capacitor Applications on 11 KV Feeder
11 KV Ex-Quality Feeder
Before Installing Capacitor
• Peak Current = 198 Amps
• Power Loss = 99.6 KW
• A.E.L
= 376752 KW
• %Power Loss = 3%
• %A.E.L
= 2%
• % V.D
= 6.1%
After Installing Capacitor
• Peak Current = 188.9 Amps
• Power Loss = 87.4 KW
• A.E.L
= 330852 KW
• %Power Loss = 3%
• %A.E.L
= 2%
• % V.D
= 4.9%
Benefits Achieved
• Current has been reduced from 198 to 188.9 Amps.
• Power loss has been reduced from 99.6 to 87.4 KW with Net Savings are 12.2 KW.
• A.E.L has been reduced from 376752 to 330852 KWH with Net Annual Savings are 45900 KWH.
• % V.D has been reduced from 6.1% to 4.9%
58
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
Why the Line Staff is reluctant to put the capacitor in
Circuit.
It has been experienced that on tripping of the feeder, the
man at the Grid Station tries to get the feeder
held/energized without getting the capacitor discharged
fully, the result of which is that the feeder does not hold.
The line staff is also not bothered about the discharge of
capacitor as well as solid earthing of the capacitor. The
residual charge at the capacitor point do not allow the
feeder to hold and thus the line staff always disconnect the
capacitor in the first instance and then forget to get intact
into the circuit.
59
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
11 KV CAPACITOR JUDGEMENT FACTORS
(Minimum kW Saving)
The following are the judgment factors in terms of kW saving accrued
from the application of capacitors which indicate their feasibility.
Capacitors
Rural
Fixed Capacitors
Urban
(Saving at Off-Peak)
450 KVAR
1.2 KW
1.2 KW
950 KVAR
1.6 KW
1.6 KW
Switched Capacitors
(Saving at Peak)
450 KVAR
8.7 KW
4.9 KW
950 KVAR
10.4 to 11 KW
5.6 to 6 KW
60
ROLE OF CAPACITOR IN DISTRIBUTION SYSTEM
11 KV CAPACITOR JUDGEMENT FACTORS
Size of the fixed capacitor, to be installed on a feeder, should
be estimated at off peak load.
If off peak load of the feeder is not available, then 1/3rd of the
peak load may be taken for calculation purposes.
Size of the switched capacitor, to be installed on a feeder,
should be estimated at peak load of the feeder.
61
WAPDA CASE
(STUDY PERFORMED BY KEL)
 Practical demonstration was performed in presence of
Chief Engineer ELR (Energy Loss Reduction), and
Managing Director Power, WAPDA.
 Sites selected:
 3-locations at Shalimar Grid Station
 Average release in (KVA)
=
18%
 Average release in capacity (KW)
=
23%
CONTINUED
62
WAPDA CASE
(STUDY PERFORMED BY KEL)
 Results were then presented, in a presentation,
to the Chairman WAPDA in the presence of
Member Power, Member Finance, number of
G.M’s and Chief Engineers.
 The Demonstration was appreciated.
CONTINUED
63
WAPDA CASE
(STUDY PERFORMED BY KEL)
 As a test case Garden Town Grid Station was
assigned for feasibility study. The following were
the results:
 Net saving claimed by KEL
= 3.2 MW
 Approximate pay back period
= 16/17 Months
 Net saving to WAPDA in 3 years = Rs. 1,11,73,000.00
64
AEB - MULTAN
Tariff
KVA
KVAR Investment Penalty
Saving Reqd.
Charged
B-2
161527 211752
B-3
45365 60779
B-4
C-1(a)
C-1(b)
6358
7629
C-2(a)
C-2(c)
2073
4224
Total 215323 284384
Payable
Period
(Month)
8962835
7
63527100
18233700 1632199
2288700
138128
1267200
208163
85316700 10941325
11
17
6
8
65
MULTAN REGION
Study Peformed By WAPDA AEB Multan (Year 1990-91)
1. KVA savings
:
2,15,323
2. KVAR required
:
2,84,384
3. Investment
:
Rs. 8,53,16,700.00
4. Penalty charged
:
Rs. 1,09,41,325.00
5. Pay back period
:
8 months
(only based on penalty)
66
AEB - FAISALABAD
Tariff
B-2
B-3
B-4
C-1(a)
C-1(b)
C-2(a)
C-2(c)
Total
Payable
Period
(Month)
6995970
2
766316
12
KVA
KVAR
Penalty
Investment
Saving Reqd
Charged
80718
25869
99929
30812
29978700
9243600
1796
915
09
4116
1591
139
1234800
47730
41700
4704
85152
13283
4983
8014
114350 144601
2404200
43380300
056043
8521468
263
6
3
4
5
67
FAISALABAD REGION
Study Peformed By WAPDA AEB Faisalabad (Year 1990-91)
1. KVA savings
:
1,14,350
2. KVAR required
:
1,44,601
3. Investment
:
Rs. 4,33,80,300.00
4. Penalty charged
:
Rs. 85,21,468.00
5. Pay back period
:
5 months
(only based on penalty)
68
ENERCON STUDY
ENERCON (National Energy Conservation Center) piloted the idea of
energy conservation and system capacity release through power factor
improvement of industry in Pakistan. The estimate made by
ENERCON, projected that power factor improvement at 2400 industrial
units had the potential of relieving around 76 MW of system capacity.
69
PENALTY FOR LOW POWER FACTOR
Average Power Factor of a consumer at the point of supply shall not be
less than 90 percent. In the event of the said power factor falling below 90
percent, the consumer shall pay a penalty of two percent increase in the
fixed charges corresponding to one percent decrease in the power factor
below 90 percent. The fixed charges for the purpose of calculating the
penalty for low power factor shall, however, be determined with reference
to maximum demand during the month.
“ Power Factor “ means the ratio expressed as a percentage of the
kilowatt-hours to the kilovolt ampere- hours consumed during the month. In
case of those connections where KVAh meters do not exist and KVARh
meters are installed, Power Factor shall be the ratio of KWh to square root
of sum of square of KWh and KVARh, i.e.
-1
P.F.= KWh
=
KWh
= Cos (Tan KVARh )
KVAh
(KWh)2+ (KVARh)2
KWh
70
71
72
73
74
75
76
77
78
SCHWABE
Inductance: 0.756
Without Capacitor
W/Capacitor 3.5 uF + - 5%
Voltage : 225 VAC
Ampere: 365 mA
Wattage: 46 W
Power Factor : 0.57
Voltage : 225 VAC
Ampere : 217 mA
Wattage : 46 W
Power Factor 0.95
Tube Light
Choke
Capacitor
Supply
79
HELVAR
Inductance: 0.91 H
Without Capacitor
W/Capacitor 3.5 uF + - 5%
Voltage : 225 VAC
Ampere: 352 mA
Wattage: 44 W
Power Factor : 0.56
Voltage : 225 VAC
Ampere : 208 mA
Wattage : 44 W
Power Factor 0.95
Tube Light
Choke
Capacitor
Supply
80