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DESIGN CALCULATION FOR VOLTAGE
IMPROVEMENT IN PRIMARY SUBSTATION BY
USING MATHCAD
Khin Trar Trar Soe1
1
Ministry of Science and Technology, Electrical Power research Department, Mandalay Technological
University, Mandalay, Myanmar, [email protected]
Received Date: February 11, 2013
Abstract
Main objective of this paper is to analyze the design of the reactive power compensation in primary
substation by using MATHCAD. This paper describes generally theory, application and design
characteristics of power factor correction and voltage improvement with shunt capacitor banks. The
locations of power factor improvement with capacitor bank at high tension side are Myaungta Gar -
Hlaw Gar- Thake Ta -Hlaingthar Yar - Bayint Naung 230 kV primary Substation in Myanmar. This
paper has been calculated by variable data. Their transmission line configuration are twin bundle
single circuit and single circuit three phase. Calculation results for capacitor bank selection
program are showed with table, chart and curve with variable data by using MATHCAD
calculation. In this paper, a plant consisting of five numbers of primary substation poor voltage
regulations is taken as a designed plant from variable data. The design plant is constructed any
condition. Capacitors have no moving parts, initial cost is low, upkeep costs are minimal, and they
are compact, reliable, and highly efficient and can be installed basically three possibilities to
correct loads individually, in groups or centrally. Therefore, in this paper capacitor banks are used
in Myanmar more than any other. Finally, suitable result selections are explained with bar chart and
curves.
Keywords: MATCHCAD Calculation, Primary Substation, Power Factor, Size of Capacitor
Banks, Transmission Line Configurations, Voltage Improvement
Introduction
Nowadays, power quality is one of the most important topics from electrical energy
consumers’ point of view. Among different power quality factors such as voltage
harmonics, voltage imbalance, voltage sag, voltage swell and flicker, it is possible to say
that voltage magnitude regulation and reactive power compensation is the most common
problems. Capacitor banks are designed for reactive power compensation in primary
distribution substation in Myanmar. They are the most common type to control reactive
power. The main objectives of this paper are to be more economical, effective utilization of
electricity and to get benefits of power factor correction. The system improvement has to
be planned properly with the following objectives in mind. To reduce loss in the distribution and sub transmission system.
To improve the voltage regulation so as to bring it within the prescribed limit.
To improve the power factor in the distribution system so as to get optimum
utilization of distribution capacitors.
Type of distribution system
The distribution system can be classified as follows:
Radial system
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Parallel or loop system
Network or grid system
Radial System
The sub-transmission substation supplies the primary distribution system feeders radiating
from the substation bus. They feed the distribution transformer of substations which step
down the voltage to distribution voltage and supply various loads through distributors.
Parallel or Loop System
From the source of supply such as sub-transmission substation, feeders are laid in parallel
to supply substations from which the secondary distribution of power will be effected. In
this system, the circuit returns to the same point so that there is in affect one feeding point
only. In case of fault in one part of the circuit, an alternative path is available giving mare
reliability than the radial system.
Primary substation
Typical distribution system consists of a primary substation and a number of receiving
substations. A typical distribution system will consist of one or more distribution
substations consisting of one or more feeders. Components of the feeder may consist of the
following:
Three-phase primary main feeder,
Three-phase, two-phase (v phase), and single-phase laterals
Step-type voltage regulators or load tap changing transformer (LTC)
Shunt capacitor banks
Three-phase, two-phase, and single-phase loads.
Network or grid system
This type of system is applicable in large distribution areas with-large loads and where the
system has to be made more reliable for continuity of supply. This is true for primary
distribution systems as well as in some applications to secondary distribution system. In
this paper, there are five primary substations of national grid system namely; Myaungta
Gar, Hlaingthar Yar, Bayint Naung, Hlaw Gar and Thake Ta. These are supplied by 230
kV overhead lines. Lines may start grid configuration from the primary substation as
shown in figure 1.
Myaungta Gar
Athoke
Kamarnat
ThatonHlaw Gar
Ywama
Bayint Naung
Thake Ta
Thanlyin
Thida
Ahlone
Sinmaleik
Hlaingthar
Yar
Figure 1. Single line diagram for primary substation (230 kV operation)
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Voltage Control Methods
A power system is said to be well designed only if it gives a good quality reliable supply
i.e. the voltage level should be within certain limits (say within ± 10%). When power is
supplied to a load through a transmission line keeping sending end voltage constant, the
receiving end load voltage undergoes variations depending upon the magnitude of the load
and power factor of the load. The higher the load with smaller power factor, the greater is
the voltage variation. Thus, various methods are adopted for voltage control.
Shunt capacitors
Series capacitors
Synchronous condensers
Tap-changing transformers
Autotransformer tap changing
Booster transformer
Shunt Capacitors
Shunt capacitors installed on a distribution system reduced the current, improve the voltage
regulation and reduce energy losses in every part of the system between capacitors and
generators. There is the capacitor for improving the voltage regulation of the system, as
well as the power factor of the system. The size of the shunt capacitor banks varies from
individual units of 5 to 25 kVA connected to the secondary of primary circuits of a
distribution system to a bank of capacitors of lager size kVA connected to the bus of a
substation at the primary side .
Table 1.Line Data for 230kV primary substation
Line Data for Primary Substation
MG-HY HY-BN MG-HG HG-TKT
Line length(mile) 22.4 6.906 19.14 13.85
Conductor size (mcmil) 605 605 605 795
Configuration Twin
bundle
single
circuit
horizontal
Twin
bundle
single
circuit
horizontal
Twin
bundle
single
circuit
horizontal
Single circuit
Horizontal
Spacing(ft) 25 25 25 25
Bundle spacing (m) 40 40 40 --
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a b c
25 ft 25 ft
40 cm 40 cm 40 cm
Figure 2. Configuration conductor between Myaungta Gar and Hlaingthar Yar
a b c
25 ft 25 ft
40 cm 40 cm 40 cm
Figure 3. Configuration conductor between Hlaingthar Yar and Bayint Naung
a b c
25 ft 25 ft
40 cm 40 cm 40 cm
Figure 4. Configuration conductor between MyaungtaGar and HlawGar
25 ft25 ft
Figure 5 . Configuration Conductor between Hlaw Gar and ThakeTa
Capacitive Susceptance:
For short lines, the total capacitive susceptance is so small that is may be omitted. In so far
as the handling of capacitance is concerned, open wire 60 Hz lines less than about 50 mile
long are short lines. Medium- Length lines are roughly between 50 and 150 mile long.
Lines more than 150 mile long require calculation in terms a high degree of accuracy is
required, although for some purposes a lumped parameter representation can be used for
lines up to 200 mile long.
Results Data for Capacitor Banks of MyauntaGar Primary Substation
The line resistance and inductive reactance are 3.8279 and 11.37763 Ω. After power factor
correction (compensation), power factor is 0.966 (lagging). When the receiving end
voltage is 230 kV, the capacitor’s size of 130 MVAR will be installed. However, the size
of capacitor will be installed 30 MVAR which is used in the form of three parallel 10
MVAR capacitor banks when the receiving end voltage is 225 kV because this power
system can be economically convenient.
Figure 6 and 7 show curve and chart of variable data for Myaungta Gar-Hlaingthar Yar
primary substation. If the receiving end voltage improves to 225 kV, size of capacitor is30
MVAR, whereas if receiving end voltage improves to 230 kV, size of capacitor is 130
MVAR for 160 MW and 70 MVAR load as shown in Fig 7. So, size of capacitor must be
chosen small size than large size for economic cost. Moreover, both receiving end voltage
and sending voltage are a little regulation. And then, maximum sending end voltage gets
230.1 kV from data collection of primary substation for one month. So, improve voltage
can choose 225 kV. The more the load increase, the more size of capacitor increase.
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225 226 227 228 229 230150
125
100
75
50
25
0
25
50
75
100
Voltage (kV), Vi
Pow
e F
acto
r,S
uppl
y C
urre
nt, S
ize
of C
apac
itors
pfi 100
Isi 100
Qi
Vi
Figure 6. Curve of variable data for Myaungta Gar – Hlaingthar Yar Primary Substation
0
50
100
150
200
250
PL(MW) 160 170 180 190 200
QL(MVAR) 70 80 90 100 110
Qr(MVAR) 30 40 50 70 80
Qr2(MVAR) 130 140 150 170 180
Voltage(kV) 225 225 225 225 225
Voltage2(kV) 230 230 230 230 230
1 2 3 4 5
Figure 7. Chart of variable data for Myaungta Gar – Hlaingthar Yar Primary Substation
ASEAN Engineering Journal, Vol 2 No 1, ISSN 2229-127X, e-ISSN 2586-9159 p.55
Results Data for Capacitor Banks of HlaingtharYar Primary Substation
The line resistance and inductive reactance are 1.18017 and 3.5077 Ω. After power factor
correction (compensation), power factor is 0.946 (leading). When the receiving end voltage
is 230 kV, the capacitor’s size of 50 MVAR will be installed which is used in the form of
two parallel 25 MVAR capacitor banks because this power system can be economically
convenient. However, the size of capacitor will be installed 270 MVAR when the receiving
end voltage is 225 kV.
Figure 8 and 9 show curve and chart of variable data for HlaingtharYar - Bayint Naung
primary substation. If the receiving end voltage improves to 225 kV, size of capacitor is
270 MVAR, whereas if receiving end voltage improves to 230 kV, size of capacitor is 50
MVAR for 70 MW and 25 MVAR load as shown in Fig 9. So, size of capacitor must be
chosen small size than large size for economic cost. Moreover, both receiving end voltage
and sending voltage are a little regulation. And then, maximum sending end voltage gets
225 kV from data collection of primary substation for one month. So, improve voltage can
choose 230 kV. The more the load increase, the more size of capacitor increase.
225 226 227 228 229 230100
60
20
20
60
100
140
180
220
260
300
Voltage (kV), Vi
Po
wer
Fac
tor,
Su
pp
ly C
urr
ent,
Siz
e o
f C
apac
ito
rs
pfi 100
Isi 100
Qi
Vi
Figure 8. Curve of Variable Data for Hlaingthar Yar - Bayint Naung Primary Substation
ASEAN Engineering Journal, Vol 2 No 1, ISSN 2229-127X, e-ISSN 2586-9159 p.56
0
50
100
150
200
250
300
PL(MW) 70 80 90 100 110
QL(MVAR) 25 35 45 55 65
Qr(MVAR) 50 60 80 90 100
Qr2(MVAR) 270 260 250 230 220
Voltage2(kV) 225 225 225 225 225
Voltage(kV) 230 230 230 230 230
1 2 3 4 5
Figure 9. Chart of variable data for Hlaingthar Yar - Bayint Naung Primary Substation
Results Data for Capacitor Banks of Hlaw Gar Primary Substation
The line resistance and inductive reactance are 3.2708 and 9.72178 Ω. After power factor
correction (compensation), power factor is 0.922 (lagging). When the receiving end
voltage is 230 kV, the capacitor’s size of 100 MVAR will be installed. However, the size
of capacitor will be installed 10 MVAR which is used in the form of ten parallel 2 MVAR
capacitor banks when the receiving end voltage is 225 kV because this power system can
be economically convenient.
Figure 10 and 11 show curve and chart of variable data for Myaunta Gar - Hlaw Gar
primary substation. If the receiving end voltage improves to 225 kV, size of capacitor is 10
MVAR, whereas if receiving end voltage improves to 230 kV, size of capacitor is 100
MVAR for 150 MW and 55 MVAR load as shown in Fig 11. So, size of capacitor must be
chosen small size than large size for economic cost. Moreover, both receiving end voltage
and sending voltage are a little regulation. Then, maximum sending end voltage gets 230
kV from data collection of primary substation for one month. So, improve voltage can
choose 225 kV. The more the load increase, the more size of capacitor increase.
ASEAN Engineering Journal, Vol 2 No 1, ISSN 2229-127X, e-ISSN 2586-9159 p.57
225 226 227 228 229 230150
125
100
75
50
25
0
25
50
75
100
Voltage (kV),Vi
Po
wer
Fac
tor,
Su
pp
ly C
urr
ent,
Siz
e o
f C
apac
ito
rs
pfi 100
Isi 100
Qi
Vi
Figure 10. Curve of variable data for Myaungta Gar - Hlaw Gar Primary Substation
0
50
100
150
200
250
PL(MW) 150 160 170 180 200
QL(MVAR) 55 65 75 85 105
Qr(MVAR) 10 5 20 30 60
Qr2(MVAR) 100 120 140 150 180
Voltage(kV) 225 225 225 225 225
Voltage2(kV) 230 230 230 230 230
1 2 3 4 5
Figure 11. Chart of Variable Data for Myaungta Gar - Hlaw Gar Primary Substation
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Results Data for Capacitor Banks of Thake Ta Primary Substation
The line resistance and inductive reactance are 1.8108 and 9.43541 Ω. After power factor
correction (compensation), power factor is 0.920 (lagging). When the receiving end
voltage is 230 kV, the capacitor’s size of 30 MVAR will be installed which is used in the
form of three parallel 10 MVAR capacitor banks because this power system can be
economically convenient. However, the size of capacitor will be installed 90 MVAR when
the receiving end voltage is 225 kV.
Figure 12 and 13 show curve and chart of variable data for Hlaw Gar - Thake Ta
primary substation. If the receiving end voltage improves to 225 kV, size of capacitor is 90
MVAR, whereas if receiving end voltage improves to 230 kV, size of capacitor is 30
MVAR for 60 MW and 20 MVAR load as shown in Figure 13. So, size of capacitor must
be chosen small size than large size for economic cost. Moreover, both receiving end
voltage and sending voltage are a little regulation. And then, maximum sending end
voltage gets 235 kV from data collection of primary substation for one month. So, improve
voltage can choose 230 kV. The more the load increase, the more size of capacitor
increase.
225 226 227 228 229 230100
80
60
40
20
0
20
40
60
80
100
Voltage (kV), Vi
Po
wer
Fac
tor,
Sup
ply
Curr
ent,
Siz
e of
Cap
acito
rs
pfi 100
Isi 100
Qi
Vi
Figure 12. Curve of variable data for Hlaw Gar - Thake Ta Primary Substation
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0
50
100
150
200
250
PL(MW) 60 70 80 90 100
QL(MVAR) 20 30 40 50 60
Qr(MVAR) 30 45 55 70 80
Qr2(MVAR) 90 75 65 50 40
Voltage2(kV) 225 225 225 225 225
Voltage(kV) 230 230 230 230 230
1 2 3 4 5
Figure 13. Chart of variable data for Hlaw Gar - Thake Ta Primary Substation
Conclusions
In this paper, the primary substation Myaungta Gar - Hlaingthar Yar, Hlaingthar Yar -
Bayint Naung, Myaungta Gar - Hlaw Gar and Hlaw Gar - Theka Ta are considered for
improve receiving end voltage by using capacitor banks. Capacitor banks will be used in
this primary substation 230 kV operation. If power system is needed to consider for
economically cost, capacitor bank will be used to control reactive power, power factor,
voltage. Installing capacitor bank at 230 kV voltage side of primary substation for voltage
improvement are benefited to reduce loss, supply current and improve power factor. The
calculated programming language used in this paper is MATHCAD software and easy to
understand, easy to modify for future expansion if necessary.
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