7/28/2019 1999 Electric and Magnetic Fields of Compact Transmission Lines.pdf

1/5

200 IEEE Transactions on Power Delivery,Vol. 14 , No . 1, January 1999

lectric and Magnetic Fields of Compact Transmission LinesMiguel O.B.C. Melo Luiz C.A.Fonseca,Non-MemberC o m m a HidroEletrica do S5o FranciscoRua Delmiro Gouveia, 333Recife -PE - 50761-901

Eduardo Fontana, Non-MemberUniversidade Federal de PernambucoDepto de Eletrbnica e SistemasRua Acad2mico H6lio Ramos sln

S. RNaidu, Member, IEEEUniversidade Federal da ParaiibaLaboratorio de AltaTensiioAV. Aprigio Veloso 882Brazil Recife-PE 50740-530 C . Grande-PB 58109-970

Abstract: Experimental and theoretical stukes of the electric andmagnetic fields produced by compact transmission lines aredescnbed. The lateral and longitudinal field profies at groundlevel w i t h rightof way have been analyzed. The studies includemeasurements of the profiles of field strength of compacttransmission lines as well as an analysis relative to the type oftower, size and type of conductor, and voltage level. Finally acomparison between measured and calculated values are presentedKeywords: Compact Transmission Lines, Electric Fields,Magnetic Fields

I. INTRODUCTIONCHESF-Companhia Hidro Elktrica do S5o Francisco,responsible for the electric power generation andtransmission in the Northeast of Brazil, plans to expand itstransinission 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 costsand economical constraints involved in the project. One ofthe conclusions of these studies is that the use of compacttransmission lines could provide several benefits, including,longer htervals between upgrades, reduction of the shuntand series reactive compensations, as well as increase of thetransmission capabilityof existing lines.PE-033-PWRD-0-04-998 A paper recommended and approved by theIEEE Transmission and Distribution Committee of the IEEE PowerEngineering Society for publication in the IEEE Transactions on PowerDelivery Manuscript submitted September 15, 1997;made available forprinting April 24, 1998

Brazil Brazil

A new type of compact transmission line known as theHigh Surge Impedance Transmission Line (HSIL)[2], with ahigher level of compactness, has been recently put intooperation in a few countries.The HSIL is a new concept of transmission line designbecause it uses a combination of features that includedistance reduction among conductors belonging to Merentphases and increase of both the number and relativedistances among sub-conductors of a single phase. Inaddition, the HSIL uses asymmetricalbundles instead of thesymmetrical and circular distribution of subconductors,employed in conventional compact lines. This newgeometric configuration equalizes and optimizes the electricfield distribution around all subconductors. The HSILoptimization process allows obtaininga substantial reductionof the series inductance as well as a sigriiiicant increase ofthe shunt capacitance, in h m producing a very high

intrinsic transmission line capability.Recent development of the HSIL technology has limitedits use to a few countries and therefore, further developmentand implementation of HSIL towers brings new challengesto experts on transmission line studies and design[3]. Thepurpose of this work is to analyze the electric and magneticfields producedby compact lines.11. STUDIEDCASES

CHESF engaged in research and development work toevaluate the performance of HSIL towers for powertransmission at 230kV As the studies showed a costreduction of approximately US$300.00/M\ toUS$600.00/MW/km, the company is jointly working withCEPEL (Center for Research in Electrical Energy) andELETRQBRAS (Brazilian holding company) to implementan HSIL system in the northeast region of Brazil.

0885-8977/99/$10.00 0 1998 IEEE

Authorized licensed use limited to: Universidad Federal de Pernambuco. Downloaded on April 27,2010 at 02:48:08 UTC from IEEE Xplore. Restrictions apply.

7/28/2019 1999 Electric and Magnetic Fields of Compact Transmission Lines.pdf

2/5

20 1

The specific HSIL design, for operation at 230 kV, thatresulted from this joint effort has the configurationillustrated n Fig. 1. It is a single circuit 230kV line and has abundle of three subconductors per phase ACSR Linnet 336kcmil and a Surge Impedance Loading (SIL) of 320MVACHESF has also developed a new upgrading technique forconventional lines, based upon the HSIL concept, called theExpanded Bundle Transmission Line (EBTL). In thisarrangement, steel hangers have been utilized to obtain anadequate increase in the distance between subconductors ofthe same phase and consequently, to reduce the seriesreactance. This strategy enables increasing from 20 to 40%of the SIL of conventional lines. This approach has beenimplemented on a 480 km TL located in the northern regionof Brazil. Figure 2 illustrates the conventional towerconfiguration for double 230 kV circuits that are inoperation in that region. It has a bundle of twosubconductors per phase ACSR Grosbeak 636 kcmil and aSIL of 406 MVA. F i g 3 shows the planned upgrade in towerconfiguration, for future operation of the system with asingle 500kV circuitwth a bundle of four subconductors perphase and a SIL of 900 MVA By using intermediate EBTL2x230kV configuration illustrated in Fig.4, it was allowedfour-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 theentire upgrade process due to financial cost reduction andextra capacity gain. 10 c

(distance inmetas)Fi g 1.HSIL tower configuration. single circuit 230 kV,threesubconductorsACSR 336 kcmil per phase

3.0 I 6.1 I 2.2 , 11.9I I I

(distance in metas)Fig ..2. Conventional transformable double circuit2x230 kV towerconfiguration,two subcondudon63 6 kanil Grosbeak per phase.1.6 , 10.3 11.9II I

(distancemmeters)Fig.3.500 kV tower configuration. four suhductors63 6 kcm il Grosbeak per phase3.0 6.1 2.2 11.9

(distance inmeters)Fig 4. E.xpanded Bundle (EB TL ) tower configuration, ouble Circuit 230kV.two ubcondud ors 636 kcmil Grosbeak per phase.

Authorized licensed use limited to: Universidad Federal de Pernambuco. Downloaded on April 27,2010 at 02:48:08 UTC from IEEE Xplore. Restrictions apply.

7/28/2019 1999 Electric and Magnetic Fields of Compact Transmission Lines.pdf

3/5

202With the increased use of HSIL towers in transmssionsystems it is important to determine the enmronmentalimpact The electric and magnetic field strength aroundtowers, wires and particularly near the ground level,represent some of the parameters requred for th sevaluation Because of the subconductors asyetnca1

geometry associated with the HSIL tower, modlfications inthe bundle equivalent radius calculations have to beintroduced in the existing computational procedures Thesemodifications also were carried out wthin theC)HESF/CEPEL/ELETROBRAS joint projectA. Electric Fields

Electric and magnetic fields are calculated using thetraditional equivalent charge method [4]-[6], for the TLgeometnes illustrated in Figs 1 through 4Figure 5 shows the lateral profiles of the ground levelelectric fields, calculated at midspan for the lines consideredin this paper Minimum distances from conductor to groundat midspan are typically. 8 m for the 230kV HSIL and EBTL2x230kV, 10 m for the 500kV line and 14m for the 2x230kV. conventional double circuit line It may be observed thatthe electric field is influenced by the distinct voltage levelsand correspondmg conductor-to-ground mnimum distances,as expected It IS also noted that the maximum electnc fieldstrength increases from 2kV/m to 4 5 kV/m when the 230kV line is converted to the EBTL confgurationThemaximum electric field for the HSIL is 5 kV/m and 11 kV/mfor the 500kV converted TL In the edge of the right-of-way(30m) is 2 5kV as illustrated in the Fig 5 , where it ISimportant to highlight that the usual maxlmum allowedelectric field in the edge of the right-of-way is 5 kV/m Thisvalue is the same recommended by IRPA for a exposurecharactenstics up to 24 h per day [6]Electric Field (kV/m) Edgeof3

right-of-

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, transformable2x230kV, EBTL 2x230kV and 500kV configurations.

Figure 6 illustrates the electnc field distributiospan of the line. The maximum calculated estrength at the tower location is approximately 3 kV/m wtha large increase occurring at midspan where the maximumvalue reaches 11 kV/m. The increase is due to the lowermdspan conductor-to-ground distance relative to that at thetower location

EkCb

11

Fig.6. Surface plot representing the electric field distnb uhon along the span ofth e 500 kV line

B. Magnetic FieldsFigure 7 shows the lateral profile of the magnetic field atmidspan. The values shown in this figure refer to the majoraxis of the field ellipse These fields are strongly dependenton the value of the transmission line current and also on theheight of the conductor above ground level [7] It is alsonoted that the maximum magnetic field increases from 20pT to 30 pT when the 230 kV line is converted into the

EBTL corQuration. These values are still lower than themaximum value of 70 pT, calculated for the 500 kVconverted transmission line.It is important to highlight that the usual maximumallowed magnetic field in the edge of the right-of-way atground level is 100 pT. This value is the same recommendedby IRPA for a exposure characteristics up to 24 h per day

[61.

Authorized licensed use limited to: Universidad Federal de Pernambuco. Downloaded on April 27,2010 at 02:48:08 UTC from IEEE Xplore. Restrictions apply.

7/28/2019 1999 Electric and Magnetic Fields of Compact Transmission Lines.pdf

4/5

Magnetic Field (pT)80

203

Electric Field (kV/m)4

-30 -20 -10 0 10 20 30Lateral coordinate (m)

Fig.7. Lateral magnetic field profiles for the HSIL 230kV, transformable2x230k17,EBTL 2x230kV an d 500kV configurations.

111.MEASURED VALUESIn order to check the theoretical calculations, which takeinto account the asymmetrical bundle geometry,measurements of the electric and magnetic fields have beenobtained for a double circuit TL. It is also expected that themeasurements will provide a better understanding of thebehavior of the electric and magnetic fields generated bycompact lines. They were performed using the equipmentFM 130-169 from the Electric Field Measurements Co. andwas realized in the Paul0 Afonso / Fortaleza transmissionline.Figures 8 and 9 show the measured and calculated fields

at midspan as a function of lateral distance. Thetransmission line under consideration is a 2x230 kVtransformable conventional line, with one of the circuitalready converted into the EBTL configuration. This mixedconfiguration is reflected in the asymmetric behavior of thefields. as can been observed in the Figs.8 and 9.These figures also indicate a good agreement betweencalculated and measured results, thus showing the suitabilityof the modified simulation method for the determination ofthe fields of compact lines.It is worth noting from Fig.8 that the measured electricfield reach to a value close to zero, 20 m away from thecentral axis of the line, and the difference with respect to thecalculated value may be attributed to the presence of a tree inthat position.

, II l

aI

-30 -20 -10 0 10 20 30--(d

Fig.8.Measured and calculated electric field profiles at midspan of a 2x230kVtransformable line having one circuit converted into the EBTL configuration.Magnetic F ield (pT)

e

0 1 I I I I 1 I-30 -20 -10 0 10 20 30

Lateral coordinate (m)

Fig.9.Measured and calculated magnetic field profiles at m idspan of a2x230kV transformable having one circuit converted into the E BTLconfiguration.

Authorized licensed use limited to: Universidad Federal de Pernambuco. Downloaded on April 27,2010 at 02:48:08 UTC from IEEE Xplore. Restrictions apply.

7/28/2019 1999 Electric and Magnetic Fields of Compact Transmission Lines.pdf

5/5

204

The results of this work can slunmarized according to

1-11 is noted that the m ~ m ~lectric field strengthincreases from 2kVlm to 4.5 kVlm when the 230 kV line isconverted into the EBTL c o ~ ~ a t i o n .owever, theseinurn value of 11 kV/m,t r ~ i s ~ s s ~ o nine. In theHSIL line the~fl f i ~ ~ dalue is 5 k V h .2-For the 500kV linefield strength at the t0~7ewith a large increase~a~~~ value reaches 11kV/m.

magnetic field strength increases from0 kV t r a n ~ o ~ a b l eine is~ a ~ o ~ .hese values are70 pT, calculated for the

20 pT to 30 pT whenconverted into the EBlower than the maxi

me t~ od or field determination of

The authors a c ~ o w ~ ~ g eessrs F. W a d and S.Gusm20 from CHESF for their relevant participation duringmea~ements, nd 0. egis (CHESF) and F. Dartfor their contrib~tions and information aboutlines .

[I ] Miguel 0 Melo, A Pessoa, V Quelroga, V Andrade, CTahan, D Brasil, W Sato, Viability Stuches of Apphcation ofCompact 500 kV Transllllssion Lmes on the CHESF (Brazil)Systems, Leningrad S ~ p o s i u ~n Compact Overhead Lznes,CIGRE, 1991[2] G N Alexandrov, Scienhfic and Engmeenng Pnnciples ofCreatmg Compact Lmes wth Increased Natural Capacity,LeningradSymposrum on CompacrOverheadLines, CIGRE, 1991.[ 3 ] Oswaldo Regis, M Maia, A Pessoa UnconvenhonalLmes ofIll& Natural PowerRatmg, An Exercise 111 Prospection 111 69 kVand 138 kV, (m Portuguese), Y.ERL;sC.CIGRE-BRAZIL, 1993[4] Electnc Power Research Institute Transmisszon LineReference Book 345 kV and Above: Second ah o n . Palo Alto,I982[5] Electnc and Magnetic Fields Produced by TransmssionSystem,CIGRE Workzng Group 36 01, Intemahonal ConferenceonLargeHigh VoltageElectnc Systems, Pans, 1980

[6] Electric Power Transmission and the Enmonment : Fields,Noise, and Interference, CER E Working Group 36.01,Intemational Conference on Large High Voltage Electr ic Systems,Pans, 1992.[7] P. S. Mmvada, Characterization of Power FrequencyMagnehc Fields 111 Different Environments,IEEE Transachonson PowerDelivery, Val 8,No 2, April 1993,pp 598-605Miguel 0. B. C.Melo was born in Recife, Brazil, in 1953.He received his B.Sc. and MSc. degrees in ElectricalEngineering from Federal University of Pernambuco, Brazilin 1976 and 1997 respectively. He is presently enrolled inthe doctoral program of the DEngineering Federal University of Paraiba. He joined theDepartment of Transmission Systeins Studies, CHESF, in1976, where he is at the present a Senior Engineer. His areaof interest includes elec~oma~eticcom~tibility,electromagnetic ransients and compact transmission lines.LuiZ C.A. Fonseca wasborn in Recife, Brazil, in 1953. Hereceived his B A . degrees in Electrical Engineering fromFederal University of Pernambuco, Brazil in 1977 andcompleted his postgraduate course 1979 by the PowerTechnologies, Inc. Mr Fonseca joined CHESF atD e m e n t of Transmission Systems Studies in 1977,where he is at the present a Senior Engineer. His area ofinterest includes transmission systems studies and powerquality.

Eduardo Fontana was born in Rio de Janeiro, Brazil, in1957. He received his B.Sc. degrees in ElectricalEngineering in 1980, and M.Sc.. degree in Physics in 1983,both fkom Federal University of Pernmbuco, Brazil. In 1989he received the Phd degree in Electrical Engineering fromStanford University, CA-USA. His past research activitieshave included microwave ferrite devices, low temperaturemagnetic materials, magnetic semiconductors, optics andfree-electron lasers. He is presently a Professor at theElectronics and Systems Department, Federal University ofPernambuco. HIS current research activities concern use ofsurface plasmon spectroscopy in thin-film technology,integrated optics devices, and in the development of opticalfiber sensors.SreeramuIu R Naidu received his B.Sc. and M.Sc. degreesfrom Indian Institute of Technology, Madras, India andIndian Institute of Science, Pangalore, India, in 1966 and1970 respectively. In 1975 he received his Phd degree byUniversity of Liverpool, United Kingdom. Dr Naidu jointFederal University of Paraiba, Brazil, where he is at thepresent a Professor of the Department of ElectricalEngineering. psis area of interest includes electromagneticfield comp ~~ tio nsnd electrical ransients computations.

Authorized licensed use limited to: Universidad Federal de Pernambuco Downloaded on April 27 2010 at 02:48:08 UTC from IEEE Xplore Restrictions apply