Download Electric and Magnetic Fields of Compact Transmission Lines

IEEE Transactions on Power Delivery, Vol. 14, No. 1, January 1999
200
lectric and Magnetic Fields of Compact Transmission Lines
Miguel O.B.C. Melo Luiz C.A.Fonseca, Eduardo Fontana, Non-Member
Non-Member
C o m m a Hidro Eletrica do S5o Francisco
Rua Delmiro Gouveia, 33 3
Recife -PE - 50761-901
Brazil
UniversidadeFederal de Pernambuco
Depto de Eletrbnica e Sistemas
Rua Acad2mico H6lio Ramos sln
Recife-PE 50740-530
Brazil
Abstract: Experimental and theoretical stukes of the electric and
magnetic fields produced by compact transmission lines are
descnbed. The lateral and longitudinal field profies at ground
level w i t h right of way have been analyzed. The studies include
measurements of the profiles of field strength of compact
transmission lines as well as an analysis relative to the type of
tower, size and type of conductor, and voltage level. Finally a
comparison between measured and calculated values are presented
Keywords: Compact Transmission Lines, Electric Fields,
Magnetic Fields
I. INTRODUCTION
CHESF-Companhia Hidro Elktrica do S5o Francisco,
responsible for the electric power generation and
transmission in the Northeast of Brazil, plans to expand its
transinission system in that regon by installing long 230 kV
and 500 kV, transmission lines (TL)[l]. In this regard,
feasibility studies have been conducted to determine costs
and economical constraints involved in the project. One of
the conclusions of these studies is that the use of compact
transmission lines could provide several benefits, including,
longer htervals between upgrades, reduction of the shunt
and series reactive compensations, as well as increase of the
transmission capability of existing lines.
S. RNaidu, Member, IEEE
Universidade Federal da Paraiiba
Laboratorio de AltaTensiio
AV. Aprigio Veloso 882
C . Grande-PB 58109-970
Brazil
A new type of compact transmission line known as the
High Surge Impedance Transmission Line (HSIL)[2], with a
higher level of compactness, has been recently put into
operation in a few countries.
The HSIL is a new concept of transmission line design
because it uses a combination of features that include
distance reduction among conductors belonging to Merent
phases and increase of both the number and relative
distances among sub-conductors of a single phase. In
addition, the HSIL uses asymmetricalbundles instead of the
symmetrical and circular distribution of subconductors,
employed in conventional compact lines. This new
geometric configuration equalizes and optimizes the electric
field distribution around all subconductors. The HSIL
optimization process allows obtaining a substantial reduction
of the series inductance as well as a sigriiiicant increase of
the shunt capacitance, in h m producing a very high
intrinsic transmission line capability.
Recent development of the HSIL technology has limited
its use to a few countries and therefore, further development
and implementation of HSIL towers brings new challenges
to experts on transmission line studies and design[3]. The
purpose of this work is to analyze the electric and magnetic
fields produced by compact lines.
11. STUDIED CASES
PE-033-PWRD-0-04-998 A paper recommended and approved by the
IEEE Transmission and Distribution Committee of the IEEE Power
Engineering Society for publication in the IEEE Transactions on Power
Delivery Manuscript submitted September 15, 1997; made available for
printing April 24, 1998
CHESF engaged in research and development work to
evaluate the performance of HSIL towers for power
transmission at 230kV As the studies showed a cost
reduction of approximately US$300.00/M\”
to
US$600.00/MW/km, the company is jointly working with
CEPEL (Center for Research in Electrical Energy) and
ELETRQBRAS (Brazilian holding company) to implement
an HSIL system in the northeast region of Brazil.
0885-8977/99/$10.00 0 1998 IEEE
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20 1
3.0
The specific HSIL design, for operation at 230 kV, that
resulted from this joint effort has the configuration
illustrated in Fig. 1. It is a single circuit 230kV line and has a
bundle of three subconductors per phase ACSR Linnet 336
kcmil and a Surge Impedance Loading (SIL) of 320 MVA
CHESF has also developed a new upgrading technique for
conventional lines, based upon the HSIL concept, called the
Expanded Bundle Transmission Line (EBTL). In this
arrangement, steel hangers have been utilized to obtain an
adequate increase in the distance between subconductors of
the same phase and consequently, to reduce the series
reactance. This strategy enables increasing from 20 to 40%
of the SIL of conventional lines. This approach has been
implemented on a 480 km TL located in the northern region
of Brazil. Figure 2 illustrates the conventional tower
configuration for double 230 kV circuits that are in
operation in that region. It has a bundle of two
subconductors per phase ACSR Grosbeak 636 kcmil and a
SIL of 406 MVA. Fig3 shows the planned upgrade in tower
configuration, for future operation of the system with a
single 500kV circuit with a bundle of four subconductors per
phase and a SIL of 900 MVA By using intermediate EBTL
2x230kV configuration illustrated in Fig.4, it was allowed
four-year postponement of the 500 kV transmission system.
It also allowed an increase of the S E . reaching 510 MVA.
This leads to a total cost reduction of US$ 10 million in the
entire upgrade process due to financial cost reduction and
extra capacity gain.
I
6.1
I
I
2.2
,
11.9
I
I
(distance in metas)
Fig..2. Conventional transformable double circuit 2x230 kV tower
configuration, two subcondudon 636 kanil Grosbeak per phase.
1.6
,
10.3
11.9
I
I
I
10 c
(distance m meters)
Fig.3.500 kV tower configuration. four suhductors
636 kcmil Grosbeak per phase
3.0
6.1
2.2
11.9
(distance in metas)
Fig 1. HSIL tower configuration. single circuit 230 kV,
three subconductors ACSR 336 kcmil per phase
(distance in meters)
Fig 4. E.xpanded Bundle (EBTL) tower configuration,double Circuit 230kV.
two subcondudors 636 kcmil Grosbeak per phase.
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202
With the increased use of HSIL towers in transmssion
systems it is important to determine the enmronmental
impact The electric and magnetic field strength around
towers, wires and particularly near the ground level,
represent some of the parameters requred for t h s
evaluation Because of the subconductors asy”etnca1
geometry associated with the HSIL tower, modlfications in
the bundle equivalent radius calculations have to be
introduced in the existing computational procedures These
modifications also were carried out wthin the
C)HESF/CEPEL/ ELETROBRAS joint project
Figure 6 illustrates the electnc field distributio
span of the line. The maximum calculated e
strength at the tower location is approximately 3 kV/m with
a large increase occurring at midspan where the maximum
value reaches 11 kV/m. The increase is due to the lower
mdspan conductor-to-ground distance relative to that at the
tower location
EkCb
A. Electric Fields
Electric and magnetic fields are calculated using the
traditional equivalent charge method [4]-[6], for the TL
geometnes illustrated in Figs 1 through 4
Figure 5 shows the lateral profiles of the ground level
electric fields, calculated at midspan for the lines considered
in this paper Minimum distances from conductor to ground
at midspan are typically. 8 m for the 230kV HSIL and EBTL
2x230kV, 10 m for the 500kV line and 14m for the 2x230
kV. conventional double circuit line It may be observed that
the electric field is influenced by the distinct voltage levels
and correspondmg conductor-to-ground mnimum distances,
as expected It IS also noted that the maximum electnc field
strength increases from 2kV/m to 4 5 kV/m when the 230
kV line is converted to the EBTL confgurationThe
maximum electric field for the HSIL is 5 kV/m and 11 kV/m
for the 500kV converted TL In the edge of the right-of-way
(30m) is 2 5kV as illustrated in the Fig 5 , where it IS
important to highlight that the usual maxlmum allowed
electric field in the edge of the right-of-way is 5 kV/m This
value is the same recommended by IRPA for a exposure
charactenstics up to 24 h per day [6]
13
Edge
of
right
-of- ’
Electric Field (kV/m)
1
K23OkV
I
4
2
0
-30
-20
-10
0
10
20
30
Lateral coordinate (m)
Fig.5. Lateral electric field profiles for the HSIL 230kV, transformable
2x230kV, EBTL 2x230kV and 500kV configurations.
1
1
Fig.6. Surface plot representing the electric field distnbuhon along the span of
the 500 kV line
B. Magnetic Fields
Figure 7 shows the lateral profile of the magnetic field at
midspan. The values shown in this figure refer to the major
axis of the field ellipse These fields are strongly dependent
on the value of the transmission line current and also on the
height of the conductor above ground level [7] It is also
noted that the maximum magnetic field increases from 20
pT to 30 pT when the 230 kV line is converted into the
EBTL corQuration. These values are still lower than the
maximum value of 70 pT, calculated for the 500 kV
converted transmission line.
It is important to highlight that the usual maximum
allowed magnetic field in the edge of the right-of-way at
ground level is 100 pT. This value is the same recommended
by IRPA for a exposure characteristics up to 24 h per day
[61.
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203
Magnetic Field (pT)
Electric Field (kV/m)
80
4
,
I
l
I
-30
-20
-10
0
10
20
a
30
I
Lateral coordinate (m)
Fig.7. Lateral magnetic field profiles for the HSIL 230kV, transformable
2x230k17,EBTL 2x230kV and 500kV configurations.
-30
-20
10
0
20
30
(
d
111. MEASURED VALUES
In order to check the theoretical calculations, which take
into account the asymmetrical bundle geometry,
measurements of the electric and magnetic fields have been
obtained for a double circuit TL. It is also expected that the
measurements will provide a better understanding of the
behavior of the electric and magnetic fields generated by
compact lines. They were performed using the equipment
FM 130-169 from the Electric Field Measurements Co. and
was realized in the Paul0 Afonso / Fortaleza transmission
line.
Figures 8 and 9 show the measured and calculated fields
at midspan as a function of lateral distance. The
transmission line under consideration is a 2x230 kV
transformable conventional line, with one of the circuit
already converted into the EBTL configuration. This mixed
configuration is reflected in the asymmetric behavior of the
fields. as can been observed in the Figs.8 and 9.
These figures also indicate a good agreement between
calculated and measured results, thus showing the suitability
of the modified simulation method for the determination of
the fields of compact lines.
It is worth noting from Fig.8 that the measured electric
field reach to a value close to zero, 20 m away from the
central axis of the line, and the difference with respect to the
calculated value may be attributed to the presence of a tree in
that position.
-10
Fig.8.Measured and calculated electric field profiles at midspan of a 2x230kV
transformable line having one circuit converted into the EBTL configuration.
Magnetic Field (pT)
e
01
-30
I
I
-20
-10
I
I
1
I
0
10
20
30
Lateral coordinate (m)
Fig.9.Measured and calculated magnetic field profiles at midspan of a
2x230kV transformable having one circuit converted into the EBTL
configuration.
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204
The results of this work can
slunmarized according to
1-11 is noted that the m
~ electric
m field
~ strength
increases from 2kVlm to 4.5 kVlm when the 230 kV line is
converted into the EBTL c o ~ ~ a t i o nHowever,
.
these
inurn value of 11 kV/m,
t r ~ i s ~ s s line.
~ o nIn the
HSIL line the ~ f l
f i ~ value
~ d is 5 k V h .
2-For the 500kV line
field strength at the t0~7e
with a large increase
~a~~~ value reaches 11kV/m.
magnetic field strength increases from
20 pT to 30 pT when
0 kV t r a n ~ o ~ a bline
l e is
~ a ~ These
o ~values
. are
converted into the EB
70 pT, calculated for the
lower than the maxi
met~odfor field determination of
The authors a c ~ o w ~ ~Messrs
g e F. W a d and S.
Gusm20 from CHESF for their relevant participation during
mea~ements,and 0.Regis (CHESF) and F. Dart
for their contrib~tions and information about
lines .
[I] Miguel 0 Melo, A Pessoa, V Quelroga, V Andrade, C
Tahan, D Brasil, W Sato, “Viability Stuches of Apphcation of
Compact 500 kV Transllllssion Lmes on the CHESF (Brazil)
Systems,“ Leningrad S ~ p o s i uon
~ Compact Overhead Lznes,
CIGRE, 1991
[2] G N Alexandrov, “Scienhfic and Engmeenng Pnnciples of
Creatmg Compact Lmes wth Increased Natural Capacity,”
Leningrad Symposrum on Compacr Overhead Lines, CIGRE, 199 1.
[ 3 ] Oswaldo Regis, M Maia, A Pessoa “UnconvenhonalLmes of
Ill& Natural Power Ratmg, An Exercise 111 Prospection 111 69 kV
and 138 kV,“ (m Portuguese), Y.ERL;sC. CIGRE-BRAZIL, 1993
[4] Electnc Power Research Institute “Transmisszon Line
Reference Book 345 kV and Above‘: Second a h o n . Palo Alto,
I982
[5] “Electnc and Magnetic Fields Produced by Transmssion
System,“ CIGRE Workzng Group 36 01, Intemahonal Conference
on Large High VoltageElectnc Systems, Pans, 1980
[6] “Electric Power Transmission and the Enmonment : Fields,
Noise,
and Interference,” C E R E Working Group 36.01,
Intemational Conference on Large High Voltage Electric Systems,
Pans, 1992.
[7] P. S. Mmvada, ”Characterization of Power Frequency
Magnehc Fields 111 Different Environments,“IEEE Transachons
on Power Delivery, Val 8, No 2, April 1993, pp 598-605
Miguel 0. B. C. Melo was born in Recife, Brazil, in 1953.
He received his B.Sc. and MSc. degrees in Electrical
Engineering from Federal University of Pernambuco, Brazil
in 1976 and 1997 respectively. He is presently enrolled in
the doctoral program of the D
Engineering Federal University of Paraiba. He joined the
Department of Transmission Systeins Studies, CHESF, in
1976, where he is at the present a Senior Engineer. His area
of interest includes e l e c ~ o m a ~ e t i c com~tibility,
electromagnetictransients and compact transmission lines.
LuiZ C.A. Fonseca was born in Recife, Brazil, in 1953. He
received his B A . degrees in Electrical Engineering from
Federal University of Pernambuco, Brazil in 1977 and
completed his postgraduate course 1979 by the Power
Technologies, Inc. Mr Fonseca joined
CHESF
at
D e m e n t of Transmission Systems Studies in 1977,
where he is at the present a Senior Engineer. His area of
interest includes transmission systems studies and power
quality.
Eduardo Fontana was born in Rio de Janeiro, Brazil, in
1957. He received his B.Sc. degrees in Electrical
Engineering in 1980, and M.Sc.. degree in Physics in 1983,
both fkom Federal University of Pernmbuco, Brazil. In 1989
he received the Phd degree in Electrical Engineering from
Stanford University, CA-USA. His past research activities
have included microwave ferrite devices, low temperature
magnetic materials, magnetic semiconductors, optics and
free-electron lasers. He is presently a Professor at the
Electronics and Systems Department, Federal University of
Pernambuco. HIS current research activities concern use of
surface plasmon spectroscopy in thin-film technology,
integrated optics devices, and in the development of optical
fiber sensors.
SreeramuIu R Naidu received his B.Sc. and M.Sc. degrees
from Indian Institute of Technology, Madras, India and
Indian Institute of Science, Pangalore, India, in 1966 and
1970 respectively. In 1975 he received his Phd degree by
University of Liverpool, United Kingdom. Dr Naidu joint
Federal University of Paraiba, Brazil, where he is at the
present a Professor of the Department of Electrical
Engineering. psis area of interest includes electromagnetic
field c o m p ~ ~ t i o and
n s electricaltransients computations.
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