Volume 3, Issue 2
ISSN: 2320-5288
International Journal of Engineering Technology &
Management Research
Journal homepage: www.ijetmr.org
Performance Analysis and Operating Characteristics of 765 KV
Transmission Line.
Sanjeev Kumar
Nisheet Soni
M.Tech Research Student
SRIT, Jabalpur
Email: sanjeevkumarsubodh@gmail.com
Assistant Professor
(Electrical & Electronics Dept)
SRIT, Jabalpur
Email: nisheetsoni@gmail.com
Abstract—Under normal, balanced steady
state conditions the performance of power
system is of primary importance in power
system. The transmission is the main
element of electrical power transmission
system. The performance of power system
is mainly depends upon the performance of
transmission line in the system. Therefore it
is necessary to calculate the voltage,
current, and power at any point on the
transmission line. The performance of
transmission line is governed by series line
resistance, and inductance and shunt
capacitance and conductance. This paper
discusses the performance analysis of 765
kv transmission line by using power circle
diagram, and loadability curve.
Keyword:—Transmission line, Power circle
diagram, Formulation of power equation for
transmission line.
1. INTRODUCTION
Increasing demand of electric power and
addition of new generation capacity to meet
the demand, necessitate enhancement of
large transmission capacity between
generation and bulk consumption points.
This can be achieved either by development
of new transmission corridor or by
enhancing the power transfer intensity of
existing transmission assets. In India the
available generation and installed capacity
has been increased many folds in the last
two decades[3]. To transfer this bulk power
from generating stations to the distant load
centers transmission system is required The
important considerations in the design and
operation of a transmission line are the
determination of voltage drop, line losses
and efficiency of transmission. These
values are greatly influenced by the line
constants R, L and C of the transmission
line. For instance the voltage drop in the
line depends upon the values of above three
line constants. Similarly, the resistance of
transmission line conductors is the most
important cause of power loss in the line
and determines the transmission efficiency.
In this paper developed the power circle
diagram which shows the performance of
EHV transmission line [5]. Firstly, they
provide an opportunity to understand the
effects of the parameters of the line on bus
voltages. Secondly, they help in developing
an overall understanding of what is
occurring on electric power system.
2. CLASSIFICATION OF OVERHEAD
TRANSMISSION LINES
A transmission line has three constants R, L
and C distributed uniformly along the
whole length of the line [2]. The resistance
and inductance form the series impedance.
The capacitance existing between
conductors for 1-phase line or from a
conductor to neutral for a 3- phase line
forms a shunt path throughout the length of
the line. Therefore, capacitance effects
introduce complications in transmission
International Journal of Engineering Technology & Management Research | Vol 3 | Issue 2 | Sep 2015
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Sanjeev Kumar, Nisheet Soni, SRIT, Jabalpur| Performance Analysis and Operating Characteristics of 765 KV
Transmission Line
line calculations. Depending upon the
manner in which capacitance is taken into
account; the overhead transmission lines
are classified as:
(i)
(ii)
(iii)
Short transmission lines. When the
length of an overhead transmission
line is up to about 50 km and the line
voltage is comparatively low (< 20
kV), it is usually considered as a
short transmission line. Due to
smaller length and lower voltage, the
capacitance effects are small and
hence can be neglected. Therefore,
while studying the performance of a
short transmission line, only
resistance and inductance of the line
are taken into account.
Medium transmission lines. When
the length of an overhead
transmission line is about 50-150 km
and the line voltage is moderately
high (>20 kV < 100 kV), it is
considered as a medium transmission
line. Due to sufficient length and
voltage of the line, the capacitance
effects are taken into account [6]. For
purposes of calculations, the
distributed capacitance of the line is
divided and lumped in the form of
condensers shunted across the line at
one or more points.
Long transmission lines. When the
length of an overhead transmission
line is more than 150 km and line
voltage is very high (> 100 kV), it is
considered as a long transmission
line. For the treatment of such a line,
the line constants are considered
uniformly distributed over the whole
length of the line and rigorous
methods are employed for solution
[7]. It may be emphasized here that
exact solution of any transmission
line must consider the fact that the
constants of the line are not lumped
but are distributed uniformly
throughout the length of the line.
3. FORMULATION OF POWER
EQUATION
Figure 1. A two bus system
Figure 1 shows the SLD of three phase
transmission line the system having two
buses. Sr is the complex power at receiving
end & Ss is the complex power at sending
end. The receiving end and sending current
is given as:
Where ABCD are the line paremeter.
Let
Therefore
The complex power at the receiving &
sending end is given by
International Journal of Engineering Technology & Management Research | Vol 3 | Issue 2 | Sep 2015
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Sanjeev Kumar, Nisheet Soni, SRIT, Jabalpur| Performance Analysis and Operating Characteristics of 765 KV
Transmission Line
5. CAPABILITY OF POWER
TRANSMISSION
4. POWER CIRCLE DIAGRAM
The receiving and sending end power is
given by eq. (X) & (Y) each of the power
is sum of two phasors. Real part of these
phasor represents real power P while
imaginary part of phasor represents
reactive power Q [8]. Is is possible to plot
Sr and Ss in x-y plane. The transmission
lines are usually operated with constant
sending and receiving end voltage then one
component of each power is constant
phasor while second component of a
phasor of constant magnitude but variable
angle.
The center of circle diagram is located at
tip of the phasor
Therefore the horizontal axis of center is
The ability of power handling capacity is
limited by thermal loading limit and
stability limit due to real power loss the
conductor temperature increased and due
to this conductor is [2] stretches this will
increase the sag between the towers the
thermal limit is specified by current
carrying capacity of conductor if current
carrying capacity is denoted by Ithermal then
Sthermal=3VratedIthermal
6. SURGE IMPEDANCE LOADING
When the line is loaded by being
terminated with impedance equal to its
characteristic impedance, the receiving end
current is
Ir= Vr/Zc
For a lossless line Zc is purely resistive.
The load corresponding to the surge
impedance at rated voltage is known as the
surge impedance loading (S1 L). given by
And vertical axis is
7. RESULT AND DISCUSSION
The radius of receiving end circle is
The circle diagram for 765kv line is shown
in fig. The locus of all points is obtained by
plotting Pr vs. Qr for fixed line voltage and
varying load angle [1]. The family of such
circles with fixed receiving end voltage
and varying sending end voltage is useful
in assessing performance of the
transmission line.
Figure 2: Receiving end power circle diagram
International Journal of Engineering Technology & Management Research | Vol 3 | Issue 2 | Sep 2015
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Sanjeev Kumar, Nisheet Soni, SRIT, Jabalpur| Performance Analysis and Operating Characteristics of 765 KV
Transmission Line
when load ability is expressed in terms of
SIL, a curve, can be used to estimate the
maximum permissible loading for a given
line length [3].
Power circle diagram Vs: from Vr to 1.1Vr
16000
14000
12000
10000
Qr, Mvar
8000
1.10
6000
1.05
4000
Loadability curve for length up to 1/4 wavelength
10
2000
1.0
9
0
SIL = 2015.0504MW, delta = 30degrees
8
-2000
7
-0.8
-0.6
-0.4
-0.2
0
Pr, MW
0.2
0.4
0.6
0.8
1
6
4
x 10
Figure 3: Receiving end power circle diagram
P.U. SIL
-4000
-1
5
4
The loadability curve
The voltage profile for 765 kv transmission
line is shown in Fig the fallowing cases are
considered for voltage profile for 765 kv
transmission line such as:
3
Thermal limit
2
Theoretical stability limit
1
0
Practical line loadability
0
500
1000
1500
Line length
Figure 5: Line Load ability Curve for 765 kv Line

Open ended line

Line terminated in SIL

Short circuited line

For full load line
REFERENCES:
[1]
Electric Power Research Institute
(EPRI), “Transmission Line
Reference Book: 345 kV and
Above,” second edition, revised,
1987.
[2]
R. Lings, “Overview of
Transmission Lines Above 700
kV,” IEEE PES 2005 Conference
and Exposition in Africa, Durban,
South Africa, 11-15 July 2005.
[3]
IEEE Standard 738-2006, “IEEE
Standard for Calculating the
Current–Temperature Relationship
of Bare Overhead Conductors,”
IEEE, 2006.
[4]
R. Dunlop, R. Gutman, and P.
Marchenko,
“Anal ytical
Development of Loadability
Characteristics for EHV and UHV
Transmission Lines,” IEEE
Transactions on Power Apparatus
and Systems, Vol. PAS-98, No. 2,
March/April 1979.
[5]
H. P. St. Clair, "Practical Concepts
in Capability and Performance of
Voltage profile for length up to 1/8 wavelength, Zc = 290.527 ohm
1100
No-load
1000
900
800
SIL
700
Vr
600
500
Rated load
400
300
200
100
Short-ckt
0
0
Sending end
100
200
300
400
500
600
700
800
Receiving end
Figure 4: Voltage Profile of 765 kV Transmission
Line.
Thermal limit Curve
To assess the load ability of a high-voltage
transmission line, planning engineers
commonly use the concept of Surge
Impedance Loading (SIL). SIL is a
convenient for measuring relative load
abilities of lines operating at different
nominal voltages. It has been shown that,
International Journal of Engineering Technology & Management Research | Vol 3 | Issue 2 | Sep 2015
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Sanjeev Kumar, Nisheet Soni, SRIT, Jabalpur| Performance Analysis and Operating Characteristics of 765 KV
Transmission Line
Transmission Lines," AIEE
Transactions (Power Apparatus
and Systems). Paper 53-338
presented at the AIEE Pacific
General Meeting, Vancouver, B.
C., Canada, September 1-4, 1953.
[6]
Electric Power Research Institute,
“Transmission Line Reference
Book: 345 kV and Above,” second
edition, revised, publication EL2500, 1982.
[7]
J. Hao and W. Xu, “Extended
Transmission Line Loadability
Curve by Including Voltage
Stability Constrains, ”Proc of
Electric Power Conference,2008.
[8]
H. Scherer and G. Vassell,
“Transmission of Electric Power at
Ultra-High Voltages: Current
Status and Future Prospects,”
Proceedings Of The IEEE, Vol.
73, No. 8. August 1985.
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