ISSN 2319-8885
Vol.03,Issue.16
July-2014,
Pages:3345-3349 www.semargroup.org, www.ijsetr.com
H
TUN
Y
U
A
UNG
1
, K
HIN
T
HUZAR
S
OE
2
1
Dept of Electrical Power Engineering, Mandalay Technological University, Mandalay, Myanmar,
E-mail: tunyuaung86@gmail.com.
2
Dept of Electrical Power Engineering, Mandalay Technological University, Mandalay, Myanmar.
Abstract: From economical point of view, transmission line system is very important in the electricity supply system. The choice of the line voltage is important to do the design of power transmission line. Different voltage systems with the same power flow have different carrying current on the line. Higher current tends to produce the higher losses. To reduce the current on the line, the line voltage can be increased. The electrical transfer of energy from one place to another over long distance with standard regulations is one of the major problems in the field of electrical power engineering. The parameters of overhead transmission line are resistance, inductance and capacitance. For three-phase line, the choice of spacing of conductors is important and the lines must be transposed to compensate the mutual inductance. In this paper, design of Chaunggu-Harkhar 66 kV overhead transmission lines and performance analysis of MV transmission system are mentioned.
Keywords: Transmission Line System, Different Voltage Level, Overhead Line, Line Parameters, 66Kv Overhead
Transmission Line.
I. INTRODUCTION
The use of electrical power is more developing in accordance with the development of the nation and more development of the living standard of the people.
Transmission line means essential link between generating station and load point. Transmission lines are a vital part of the electrical system, as they provide the path to transfer
Power between generation and load. Transmission lines operate at high voltage levels, and are ideally tightly interconnected for reliable operation. The length of transmission lines, the amount of power transmitted, short circuit levels, stability requirements have also become paramount importance. Most high voltage transmission systems are interconnected in a network system of circuit elements. In order to transmit heavy power efficiently for any considerable distance, comparatively high voltage is required. So, economic choice of voltage should be considered for any power transmission line. The selection of size of the conductor is also important in order to carry the amount of enough current that flows on the line due to the transfer of power. Moreover, the amount of power losses and voltage drop on the line should be in an acceptable range as in the standard regulations.
In transmission system, there are two kinds of transmission line, namely overhead lines and underground cables.
Overhead line transmission system is cheaper than underground cable system. But maintenance cost for overhead line is higher than that of the underground cables
The resistance of an overhead line produces the power loss and the capacitance will affect the voltage of sending end an the receiving end. If the lines have very much capacitance effect, the reactors must be used to compensate the capacitance effect. The inductance of an overhead transmission line may interfere to the nearby communication channel. In highly induction line, the mutual induce voltage in the telephone line is dangerous for the people who use the telephone. Therefore for the three-phase line, the choice of spacing of conductors is very important and the lines must be transposed to compensate the mutual inductance if needed.
II. TYPES OF CONDUCTOR
In the early days of transmission of electric power conductor were usually copper but aluminum conductors have completely replaced copper because of the much lower cost and lighter weight of aluminum conductor compared with a copper conductor of the same resistance. The fact that an aluminum conductor has a large diameter than a copper conductor of the same resistance is also an advantage. With a larger diameter the line of electric flux originating on the conductor will be farther apart at the conductor surface for the same voltage.[47Woo] Different types of aluminum conductors are as follows;

AAC ; all-aluminum conductors

AAAC; all-aluminum-alloy conductors

ACSR; aluminum conductor steel-reinforced

ACAR; aluminum conductor alloy-reinforced
ACSR (aluminum conductor steel-reinforced) is the most wildly used conductor material, having particular application
Copyright @ 2014 SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved.

H TUN Y U A UNG , K HIN T HUZAR S OE at high voltage. It is made up of galvanized steel core one or more strands, and one or more outer layers of aluminum wire. The conductivity is taken to be that of the aluminum alone, and the strength to be 85 percent of the sum of the steel wire plus 95 percent of the sum of the aluminum wires. f = system frequency in Hz
µ= permeability = 1.0 for non-magnetic material
R dc
= dc resistance in Ω/mile
TABLE I: Skin Effect
A. Line Constants
The transmission line is an electric circuit which has four constants, that is resistance R, inductance L, capacitance C and leakage admittance y and it is necessary to fully understand these line constants so as to calculate its electrical characteristics.
B. Resistance
The resistance of transmission line conductors is the most important cause of power loss in a transmission line. The term resistance, unless specifically qualified, means effective resistance. The effective resistance of a conductor is
R = power loss in conductor
I
2
(1)
Where the power is in watt and I is the rms current in the conductor in amperes. The effective resistance is equal to dc resistance of the conductor only if the distribution of current throughout the conductor is uniform.
Direct current resistance is given by the formula.
(2)
Where ρ = resistivity of conductor l = length
A = cross-sectional area
The resistance of a conductor at any temperature is
R
2
R
1

T o
T o


T
2
T
1
(3)
R
1
and R
2
are the resistance of conductor at temperature
T
1 and T
Celsius.
2
. T
1
and T
2
are conductor temperature in degrees
T
0
= constant varying with conductor material
= 234.5 for annealed copper
= 241 for hard-drawn copper
= 228 for hard-drawn Aluminum
C. Skin Effects
Uniform distribution of the current throughout the cross section of a conductor exists only for direct current. As the frequency of alternating current increase, the non-uniformly of distribution become more pronounced. An increase in frequency causes non-uniform current density. This phenomenon is called skin effect. In resistance calculation the following formula should be used to consider the skin effect,
D. Inductance
When the conductors of three-phase line are not spaced equilaterally, the problem of finding the inductance becomes more difficult. Then the flux linkages and inductance of each phase results in an unbalanced circuit. Balance of the three phase can be restored by exchanging the position of conductors at regular intervals along the line so that each conductor occupies the original position of every other conductor over an equal distance .Such an exchange of conductor position is called ‘transposition’.[85Cot]
The inductance per phase in bundle is
L

2

10

7 ln
D eq
D s
Where,
D eq
= equivalent GMD
D s
= GMR of the conductor
The inductive reactance,
H m
(6)
(7)
TABLE II. Self-GMD or GMR of Stranded Conductors
Where, K is a function of X.
X = 0.63598
(4)
μf
R dc (5)
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.16, July-2014, Pages: 3345-3349

Design and Analysis of 66 kV Transmission Line
E. Capacitance
Capacitance to neural is the ratio of the change on a conductor to the voltage between that conductor and neutral.
B. Economic Size of Conductor
Kelvin’s Law may be represented by the following formula in case of aluminum conductor.
Where,
D eq
= equivalent GMD
r = radius of conductor
k = 8.85x10
-12
F/m
The capacitive reactance,
(8)
(9)
F. Surge Impedance
In transmission system, characteristic impedance is called surge impedance. It is usually reserved for the special case of a losses line. If a line is lossless, its resistance and conductance are zero and the characteristic impedance reduces as,
C

0.013
a.p
(Ampere/mm
2 q
) (13)
Where,
C = most economical density of current (Ampere/mm
2
) a = percent annual expense to the construction cost of conductor p = price of conductor (kyat/kg) q = cost of electricity (kyat/kWh)
The current I is work out as follows:


(
3
) (14)
Where,
µ = utility factor being (0.6 ~ .15)
pf = power factor being 0.85
V = line voltage (kV)
P = Maximum Power (kW)
The most economic size of conductor = A = I/C (mm
2
).
Where,
(10)
X
L
= series inductance per unit length of the line
X
C
= shunt capacitance per unit length of the line
These X
L
and X
C
are the basic parameter of the transmission line.
F. Surge Impedance Loading (SIL)
Surge Impedance Loading (SIL) of a line is the power delivered by a line to a purely resistive load equal to its surge impedance. Under this condition the sending-end and receiving-end voltages are equal in magnitude but different in phase position. Surge impedance loading in itself is not a measure of maximum power that can be delivered over line.
C. Choice of Conductor by Corona Voltage
Critical voltage of corona formation of conductor is worked out by the following formula.
V c

24.3
3 m
0 m
1
δ dlog
2D d
(kV) (15)
Where,
V
C
= disruptive critical voltage in kV (line to line) m
0
= factor of irregularly of conductor surface being 0.8 m
1
= factor of weather being 1 in fair weather and 0.8 in rainy weather
δ = factor of air density being 1.0
D = spacing of conductor (cm) d = Diameter of conductor
Where,
(11)
V
LL
= line to line voltage (kV, rms),
I
LL
= line current at surge impedance loading in ampere.
D. Contamination Design for Porcelain Insulator
The target withstand voltage for contamination design can be calculated with the following Equation,
III.
DESIGN AND CONSTRUCTION FOR 66KV
TRANSMISSION LINE (CHAUNGGU-HARKHAR)
A. Selection of Transmission Line Voltage
It is very important to select proper voltage level for a transmission line because that will lead to many consequences in operation of power system and if there is an incorrect decision by a designer or decision marker, it is very difficult and costly to solve the problems in future. Generally the supply power and the line length will be given; the most economic voltage can be determined by the following equation.[88Tur]
(16)
The design withstand voltage of each insulator discs is proportional to the number of insulator strings. The flashover voltages of insulator discs of 10″ dia. × 5¾″ spacing are shown in Table.
TABLE III. Flashover Voltages of 10″ dia. × 5¾″of
Insulator Discs
V

5 .
5 L

Load in
150
KVA
( KV )
(12)
Where,
L = Line length in mile.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.16, July-2014, Pages: 3345-3349

H TUN Y U A UNG , K HIN T HUZAR S OE
IV.
DESIGN AND CALCULATION OF 66KV
TRANSMISSION LINE
Line Data,
Total Line Length
Transmitted Power
System Frequency
Phase Spacing
= 166km (103 mile)
= 6MW
= 50 Hz
= 6.5m
Line configuration = Horizontal
66

3.8

145 kV
3
TABLE IV: Line Voltage and Number of Insulators Used
Economic voltage selection,

5.5
103

6000 kV
150

65.77
kV
(17)
The numbers of insulator discs are decided as follows:
Suspension Insulator – 5 units
Tension Insulator – 6 units (Double string of 12 units)
Economic voltage = 65.77 kV
So, selected voltage = 66kV
Economic size of conductor,
The insulation of the line approaching within a mile from
Power Station or Sub-station would be reduced by decreasing the number of insulator discs in order to have the insulation co ordination with the insulation strength of station equipment.
Most economical density of current,
(18)
(19) a = 20% p = 2500 kyat/kg q = 50 kyat/ kWh
C

0 .
013
0.2

2 500

0 .
41
A/mm
2
50
Power factor, pf = 0.85
Utility factor, µ = 0.75
Load current, I =
μ
P
3

V
 p.f
=
0.75

6

10
3
3

66
= 46.31A
A

I
C

46.31

112 .
95 mm 2
0.41
Economic cable size = 367.8 MCM (185 mm
2
)
Consideration for choice of conductors by corona voltage,
V
C

24.3

3

0 .
8

1 .
0

1 .
0

1 .
9177
2

650 log
1.9177
(20)
= 182.811 kV
Line constant calculations are as follow;
Line Data
Line length = 103 miles
Conductor size = 367.8 MCM
Outside diameter = 0.755 in
Conductor spacing = 6.5 m = 21.325 ft
Configuration = horizontal
Line voltage = 66 kV
Resistance Calculation,
At 20˚C,
R dc

ρ
A
Ω/mile
X

0.063598
(21)
1

50
0.2735

0 .
8599
By using linear interpolation, from Table,
K

1 .
00212

( 1 .
0034
( 0 .
9


1 .
0
00212
.
8 )
)

( 0 .
8599

0 .
8 )
K = 1.002887
Rac = 1.002887 × 0.2735= 0.2743 Ω/mile
Line Inductance Calculation, L
Corona critical voltage, V
C
= 182.811kV (Line to Line)
Thus, 367.8MCM, ACSR conductor should be chosen to avoid from corona effect.
Number of insulator:
Internal abnormal voltage (kV) = Normal operating voltage
(kV)× 3.8
D

3 eq

3 D ab
D bc
D ca (22)
21.325


21.325
26 .
87 ft

42.65
For 26-strands,
Ds= 0.809 R

0 .
809

0 .
755
2

12

0 .
02545
L

2

10
7 ln
D eq
D
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.16, July-2014, Pages: 3345-3349 s
H/m ft

Design and Analysis of 66 kV Transmission Line

2


10
7
1 .
ln
3924
26.87
10
-6
H/m
0.02545

H/m
Inductive reactance, XL = 2 π f L
= 2 π × 50 × 1.3924 ×10-6×1609
= 0.7038 Ω/mile stringing the conductors, sags for different spans with poles at equal or unequal height. Transmission line tower with fabricated steel members are used in this MV transmission.
The transmission lines are made more wind- resistant as they are to bear out the wind pressures during storms and cyclones. Problems of transportation and erection arise as the supporting structures are to be transported over long
Line Capacitance Calculation, C
C n

2

D k ln ( eq r k = 8.85×10
-12
F/m
D eq
= 26.87ft
)
(23)
R

0 .
755
(2

12 )

0 .
03146
2
 ft

8 .
85

10

12
C n
 ln (
26.87
0.03146
)
Capacitive reactance, X
C
= 1/2 π f C
= 0.24×10
6 Ω/mile
Parallel Admittance, y y = g + j ω C n
= j 2 π f C n
Ʊ/m ( g is neglected )
= j 2 π × 50 × 8.238 ×10
-12
×1609
= j 4.164 ×10
-6 Ʊ/mile distances and standard workman- ship is required for erection of the transmission lines. The demand of electric power is increasing throughout the world and in many countries it is doubling every five to eight years. The increasing demand of electric power has to be met; but it is presenting unusual problems to the power engineers. For developing power systems and transmission lines, and for the economical transmission of large blocks of power over long distances, it is necessary to go in for higher and higher transmission voltages.
VI. ACKNOWLEDGMENT
The author would like to express grateful thanks to his supervisor Dr.Khin Thuzar Soe, Associate Professor and to all his teachers from Department of Electrical Power
Engineering, Mandalay Technological University for their encouragement and helpful suggestions. And the author also would like to express his gratitude to his parents for their support and encouragement.
Surge impedance, Z
0
=
X
L
X
C
X
L
X
C
= 0.7038 Ω/mile
= 0.24×10
6
Ω/mile
Z
0
=
0.7038
Surge Impedance loading:

0 .
24

10
6 
410 .
99

Z = 77.8 ∟68.71 Ω
Y = 0.4288×10
-3
∟90 Ω
(24)
SIL3Ø


I
L

V
LL
3

Z
Y
(25)
3
66000

425 .
54

3

66000

89 .
46
89.46
A

10 .
2267 MW
VII. REFERENCES
[1] korea international cooperation agency, korea electric power corporation, kepco., “feasibility study and basic designs for the 500 kv transmission system in myanmar”, final report ad appendix. (2005).
[2]Deshpande, m. v, “electrical power system design”, mc graw.hill publishing company ltd, (2000).
[3]Turan gonen, “electric power transmission system engineering” (analysis and design), john wiley &sons, inc.,
(1988).
[4]Cotton h. and barber h., “transmission and distribution of electric energy”, hodder and stoughton, (1985).
[5]Woodruff,l. f., “principles of electric power transmission”, john wiley and sons, inc. (1947).
[6]Myanma electrical power enterprise, myanmar.
[7]Ministry of electric power, Myanmar.
V.
CONCLUSION
In this thesis, the design and calculation of the Chaunggu-
Harkhar 66 kV overhead transmission line is presented. Both of the electrical and mechanical designs are also considered.
In the electrical design, choice of voltage, size of conductors, spacing of conductors, corona losses, regulation and efficiency of the line were considered. In the mechanical design, it included types of poles or tower, span to be used, number of insulators in string, size of the ground wire, location of ground wire on towers, permissible tension in
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.16, July-2014, Pages: 3345-3349