Download II. Electrostatic Effects

International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Influence of Electrostatic Effects on Conductive
Objects in the Vicinity of Overhead
Transmission Line
Mya Thida Tun, Aung Ze Ya

Abstract— To transmit electricity, overhead transmission lines
are sometimes passed through near the residential zones. These
transmission lines have harmful environmental effects.
Therefore, the electrostatic effects of overhead transmission
lines on the vicinity of conductive objects are needed to consider
preventing the person from hazards. This paper presents the
electrostatic effects on conductive objects. The transmission line
voltage of 132 kV and 230 kV are studied for electrostatic effects
on automobile, building and fence. The results are solved by the
help of Matlab Program. The induced voltage and shock current
on automobile, building and fence are calculated.
Index Terms— electrostatic, induced voltage, shock current and
conductive objects.
I. INTRODUCTION
A time-varying electric fields are induced in the vicinity of
AC power transmission systems. Due to increase in
transmitted voltages and currents, possible problems
associated with electrostatic coupling between the overhead
AC transmission line and conductive objects increase. When
a conductive object insulated from ground is in the vicinity of
overhead lines, the conductive object picks up a
electrostatically induced voltage that is proportional to the
transmission line voltage. Electric fields from high voltage
AC power lines can be hazard for personal and public that
may be in contact or in proximity with a conductive object
which is within the right-of-way of high voltage power lines.
Most conductive objects in the vicinity of overhead
transmission lines are fences of industries and buildings. So,
conductive objects existing overhead transmission lines
right-of-way (ROW) are studied in this paper. To mitigate the
effects of electric field levels from high voltage lines on
human beings living or working close to the lines, any
building constructed along the high voltage lines should have
right location along the corridor. The shock currents by
induced voltage in objects due to electrostatic effects of
overhead transmission lines should be less than “let-go”
current.
II. ELECTROSTATIC EFFECTS
In this paper, the electrostatic effects are analysed based on
the evaluation of electric field, shock current and induced
voltage on conductive objects.
A. Calculation of Electric Field
The electric fields are calculated by the Gauss equation.
The horizontal component of electric field is:
Q
Ex 
sin φ 
(1)
2πεx
and the vertical component of electric field is:
Q
Ev 
cosφ 
(2)
2πεx
Where
Q = the charge on the conductor, C/m
x = the radial distance, m
φ = angle between the electric vector and its vertical
components
Ds = self-geometrical mean distance, m
hi = height of conductor, m
Dij = distance between conductor i and image conductor j, m
dij = distance between conductor i and conductor j, m
hj = height of the conductive object, m
i
hi
j
Dij
Air
Earth
hi
Image of
conductor i
Manuscript received May 18, 2014.
Mya Thida Tun, Department of Electrical Power Engineering,
Mandalay Technological University, (e-mail: [email protected]).
Mandalay, Myanmar, +9595062788
Aung Ze Ya, Department of Electrical Power Engineering, Mandalay
Technological University, Mandalay, Myanmar, +9595038549, (e-mail:
[email protected])..
dij
dij
Image of
conductor j
Fig.1 Geometric layout of conductors and their images
The charge Q on the conductors is determined through the
voltage V and Maxwell potential coefficients P with matrix
equation.
1
All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Q  P1V 
(3)
The element of the shunt capacitance matrix is computed
from the geometry of the tower configuration as shown in
Fig.1.and from the conductor radii [3]. The capacitance is:
1
(4)
C  P
Then, the diagonal element becomes:
2h
1
(5)
Pii 
ln i
2πε0 Ds
and the off- diagonal element is
Dij
1
Pij 
ln
(6)
2πε0
dij
  
TABLE II
TRANSMISSION LINE PARAMETER
Specifications
230 kV line
132 kV line
Length
26.162 km
34.1342 km
Phase spacing, di
8m
6m
Height
of
conductor ,hi
Number of bundles, N
14 m
12.2 m
2
_
Bundle diameter, D
0.381 m
_
The system is for 230 kV AC power transmission line is
parallel with a conductive object as shown in Fig.2.
B. Calculation of Shock current
Shock current on object is occurred, when induced voltage
is inserted in the object.
object
The amount of shock current on conductive objects is,
I shock  jωEv S
(7)
Where
ω = angular frequency, rad/sec
ε0 = permittivity of free space F/m
S = charge collecting area of the object, m2
Ev = vertical components of electric field, V/m
C = Capacitance of the object, F
Fig .2. Object paralleled with power line phase conductors a,b,c
C. Calculation of Induced voltage
The electrostatically induced voltage on conductive object
is mainly due to the effect of capacitive coupling between
overhead transmission line and object [1].
The electrostatically induced voltage on conductive object,
I
(8)
V  shock
jC
In this paper, automobile, buildings and fence are studied
as the conductive objects.
The electrostatic effect on the building has been analysed at
the three different types of building (type 1 is house insulated
roof conductive building, type 2 is house conductive roof
insulated building and type 3 is house and roof conductive
building).
Distance between middle conductor and conductive object,
dj is 13.5 m. The calculations are for the distance between
middle conductor and object, from 0 to 50 m, line-to-line
voltage of 132 kV and 230 kV.
IV. ANALYSIS RESULTS
III. SYSTEM MODEL PARAMETERS
The following is the list of parameters used in this study:
A. Shock Current on Fence
14
TABLE I
CONDUCTIVE OBJECTS
230 kV
132 kV
12
Specifications
Fence
Automobile
Building
Capacitance to
ground, C
Length
11.15 nF
1800 pF
6.22 nF
1.5 km
10.4 m
100 m
Height
1.8m
2.4 m
33.5 m
width
-
2.8 m
50 m
4
Radius
of
fence wire, rf
2.032 mm
_
_
2
Height of roof
_
_
12.5 m
Charge
collecting area
of the object, S
2268.1
m2
89.856
m2
System
Separation distance: range from 0 to 50 m
Shock current (mA/m)
10
8
6
0
0
5
10
m2
(type 1) 20167
(type 2) 17487 m2
(type 3) 24924 m2
15
20
25
30
distance dj (m)
35
40
45
50
Fig.3 Shock current on fence due to electrostatic effect
Shock current on fence is occurred when induced voltage is
inserted in the fence. Based on the electrostatically induced
2
All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
voltage on the fence as shown in Fig.6, the shock current on
fence is calculated. The calculated results for shock current on
fence due to electrostatically induced voltage are shown in
Fig.3 for various distances between middle conductor and
fence. As it is the shock current of electrostatically induced
voltage, the capacitance of the fence is needed to consider
calculating the current. The maximum shock current on fence
is about 12.2324 mA/m at the distance 13.5 m between middle
conductor and fence. The minimum shock current on fence is
occurred at fence under middle conductor. The shock current
is sharply increased the distance 7-13.5 m between middle
conductor and fence. Beyond that distance, the shock currents
are slightly decreased. The shock current due to 230 kV on
transmission line is higher than others, and due to 132 kV on
line is lower than others.
B. Shock Current on Automobile
Fig.4 shows the shock current on automobile due to 230 kV
and 132 kV overhead transmission line for various distances
between middle conductor and automobile.
The maximum shock current on automobile is 0.4846
mA/m about at the distance 13.5 m from the middle conductor.
When the automobile is under middle conductor, the shock
current on automobile is minium. The shock current on
automobile is slightly reduced by increasing the distance
between middle conductor and automobile
The maximum shock current on type 3 building is
134.4205 mA/m about at the distance 13.5 m between middle
conductor and building. The minium shock current on type 2
building is occurred at building is under the middle conductor.
The shock current due to type 3 building is higher than others,
and due to type 2 building is lower than others. It can be
regarded as the level of shock current on the buildings
decrease with the increasing the separation distance between
middle conductor and buildings.
D. Induced voltage on Fence
Fig.6 shows the induced voltage on fence due to 230 kV
and 132 kV on overhead transmission line for various
distances between middle conductor and fence. The voltage
induced on the fence is of electrostatically induced voltage. It
is due to the effect of capacitive coupling between overhead
lines and fence. For the study, the maximum induced voltage
on the fence is 3.4916 kV/m at the distance 13.5 m from the
middle conductor. Beyond that distance, the coupling effect
reduces slightly and for that reason, the induced voltage on
fence is less, and the least at far distance. But when the fence
is under middle conductor, the induced voltage on the fence is
least.
3.5
3
0.5
230 kV
132 kV
Induced voltage (kV/m)
0.45
0.4
Shock current (mA/m)
230 kV
132 kV
0.35
0.3
2.5
2
1.5
1
0.25
0.2
0.5
0.15
0
0
0.1
0.05
0
5
10
15
20
25
30
distance dj (m)
35
40
45
Shock current (mA/m)
20
25
30
distance dj (m)
35
40
45
50
0.9
(type 1 building)
(type 2 building)
(type 3 building)
(type 1 building)
(type 2 building)
(type3 building)
230 kV
132 kV
0.8
0.7
Induced voltage (kV/m)
140
100
15
E. Induced voltage on Automobile
C. Shock Current on Building
The calculated results for shock current on buildings is
shown in Fig.5 for various distance between middle conductor
and buildings.
230 kV
230 kV
230 kV
132 kV
132 kV
132 kV
10
Fig.6. Electrostatically induced voltage on fence
50
Fig.4. Shock current on automobile due to electrostatic effect
120
5
0.6
0.5
0.4
0.3
0.2
80
0.1
60
0
0
5
40
10
15
20
25
30
distance dj (m)
35
40
45
50
Fig.7. Electrostatically induced voltage on automobile
20
0
0
5
10
15
20
25
30
distance dj (m)
35
40
45
50
Fig.5. Shock current on buildings due to electrostatic effect
The induced voltage on the automobile is of electrostatic
induced voltage. It is mainly due to capacitive coupling
between overhead line and automobile. Fig.7 shows the
3
All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
induced voltage on automobile due to 230 kV and 132 kV
overhead transmission line for various distances between
middle conductor and automobile.
Based on the electrostatically shock current on automobile
as shown in Fig.4, the induced voltage on automobile is
calculated.
For this study, the maximum induced voltage on
automobile is about 0.857 kV/m at the distance 13.5 m from
the middle conductor and it decreases slightly with distance.
When the automobile is under the middle conductor, induced
voltage on automobile will be minium level. The induced
voltage due to 230 kV on transmission line is higher than due
to 132 kV on transmission line.
F. Induced voltage on Building
Fig.8 is the calculated results of induced voltage on
building due to 230 kV and 132 kV over head transmission
line for various distances between middle conductor and
building.
Based on the electrostatically shock current on building as
shown in Fig.5, the induced voltage on building is calculated.
The induced voltage on the building is highest at type 3
building and is lowest at type 2 building at the same distance
from middle conductor. The peak induced voltage on the
building for the study is 68.79 kV/m at the distance 13.5 m
from the middle conductor. The induced voltage due to type 3
building is higher than others, and due to type 2 building is
lower than others.
maximum shock current on fence for the study is about
12.2324 mA/m. The maximum shock currents on building and
fence are higher than the current magnitude of 5 mA
maximum “let-go” current [2]. So to safe for a person in
touching the conductive object, the conductive object should
be grounded.
VI. CONCLUSION
Electrostatic effects caused by high voltage overhead
power transmission lines on neighboring, parallel conductive
objects have been analyzed. For the study, 132 kV and 230
kV AC transmission lines are used and automobile, building
and fence are studied as conductive objects. Due to the
electrostatic effect, high induced voltage on the conductive
objects is occurred. For any conductive objects in the vicinity
of overhead transmission lines should be grounded.
ACKNOWLEDGMENT
The author would like to express grateful thanks to her
supervisor Dr. Aung Ze Ya, Associate Professor, Department
of Electrical Power Engineering, and to all her teachers from
childhood till now, especially Dr. Min Thu San, Associate
Professor, Department of Myanmar Scientific and
Technological Research, Yangon. The author’s special thanks
are sent to her father, mother and aunt, for their guidance and
support for all times.
REFERENCES
[1] Transmission Line Reference Book-345 kV and Above 2nd ed.,
Electrical Power Research Institute, Palo Alto, CA, 1982.
[2] Electrostatic and Electromagnetic Effects of Overhead Transmission
Lines, REA Bulletin 62-4, United States Department of Agriculture,
May, 1978.
[3] Electric Power Generation, Transmission and Distribution 2nd ed.,
Leonard L. Grigsby, 2007.
[4] Electrostatic and Electromagnetic Effects of Ultrahigh-Voltage
Transmission Lines, EL-802, Research Project 566-1, June 1978.
[5] EPRI Transmission Line Reference Book-115-230 kV Compact Line
Design,2007.
[6] Transmission and Distribution of Electrical Power, Dr. Houssem Rafik
El- Hana BOUCHEKARA, 2009/2010.
70
230 kV
230 kV
230 kV
132 kV
132 kV
132 kV
Induced voltage (kV/m)
60
50
type 1
type 2
type 3
type1
type2
type3
40
30
20
10
0
0
5
10
15
20
25
30
distance dj (m)
35
40
45
First A. Author ― M s . M y a T h i d a T u n
Place
― Room no: 2 47, Manthazin
Hostel, MTU, Mandalay
Date of birth
― 1.5.1980
50
Fig.8. Electrostatically induced voltage on buildings
V. DISCUSSIONS
The voltage induction effects of overhead transmission
lines on conductive objects are governed by the amount of
capacitive coupling, inductive coupling and resistive coupling.
For the study, the effect of capacitive coupling is considered.
Increasing the applied voltage will increase the induced
voltage on the conductive objects due to the effect of
capacitive coupling. The differences in induced voltages and
shock currents are occurred when the lateral distance of
conductive objects is increased.
As the maximum shock current on the automobile for the
study is about 0.4846 mA/m, it is less than the maximum
“let-go” current magnitude of 5 mA. But the peak shock
current on the type 3 building is 134.4205 mA/m and the
Ms. Mya Thida Tun received her B.E. degree in
Electrical Power Engineering from Technological
University, Meikhtila, Mandalay Division,
Myanmar, in February 2004. Afterwards, she
received M.E. degree in Electrical Power Engineering
from West Yangon Technological University (WYTU), Hlaingtheryar township,
Myanmar, in October 2010.
She worked as an assistat lecturer in the Department of Electrical
Power Engineering at Technological Collage, Kyaukpadaung Township,
Mandalay Division in Myanmar from April 2004 to Dec 2009. Currently, she is
an lecturer in the Department of Electrical Power Engineering at Technological
University, Pinlon, Shan State in Myanmar since Jan 2010.
Ms. Tun is currently a Ph.D. candidate in the Department of Electrical
Power Engineering at MTU, Myanmar. Her research interest is in the high-voltage
transmission lines with a special emphasis on analysis and reducing the
environmental effects of high-voltage AC transmission lines.
4
All Rights Reserved © 2012 IJSETR