A Modified OPGW Cable to Account for Higher Temperature Capacity During Short Circuit and Lightning Events

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1 A Mdified OPGW Cable t Accunt fr Higher Temperature Capacity During Shrt Circuit and Lightning Events Jã T. Pinh 1, Sérgi Clle 2, Victr Dmitriev 1, Luciana Gnzalez 1, Júli N. Scussel 2, Marcel A. Andrade 3, Jã C. V. da Silva 3, Maur Bedia 3 1 Department f Electrical Engineering / Federal University f Pará Belém Pará Brazil jtpinh@ufpa.br 2 Department f Mechanical Engineering / Federal University f Santa Catarina Flrianóplis Santa Catarina Brazil clle@emc.ufsc.br 3 Prysmian Telecmunicações Cabs e Sistemas d Brasil S.A. Srcaba Sã Paul Brazil marcel.andrade@prysmian.cm Abstract This paper presents a cncept f an OPGW cable, which was designed t ptimize its highest temperature capacity, t accunt fr the high current regimes present at shrt circuit and lightning events, which may ccur during nrmal peratin, and cause severe faults, even resulting in the rupture f the cable. Cncerning the thermal effects, a cable with the prpsed cnfiguratin was manufactured and preliminary shrt circuit tests were perfrmed fr cmparisn with the calculated results using the analytical mdel develped. Fr the electrmagnetic effects, simulatins were carried ut using the finite element methd and the results fr the prpsed structure (aluminum cvered steel/aluminum ally) are cmpared t thse f three ther different cnfiguratins: armr steel wires nly, steel and aluminum ally, and nly aluminum cvered steel. Keywrds: Mdified OPGW cable, numerical analysis, current density, skin effect, temperature capacity. 1. Intrductin The OPGW is a multilayer structure, which is specially designed t be installed as verhead cable n pwer transmissin lines t prtect them against lightning, and simultaneusly transmit infrmatin thrugh its ptical fibers. The verhead lines present sme advantages cmpared t undergrund cables such as lwer installatin and maintenance csts [1], better safety, and since the ptical fibers pack is placed in a metal tube in the center f the cable structure, they are immune t electrmagnetic interference. Thus, the cable can be used fr high-speed transmissin f data and t be part f lng distance telecmmunicatin lines with high reliability [2]. A typical OPGW is cmpsed f a dielectric cre (ptical fibers pack) prtected by an aluminum tube, which is cvered by armr wires usually made f steel [3-5]. Althugh these armr wires can vary in number, the cable cnsidered in this wrk is made f 12 wires at all analyzed structures. In the OPGW the physical parameters as thermal and electric cnductivity are different fr each layer and, cnsequently, the current distributin and the heat generated by Jule s Effect during the ccurrence f a shrt circuit r lightning are nt unifrm [2]. The physical and gemetrical characteristics f the cable determine the degree f damage that can ccur. Therefre, the gal f the mdified cable is t btain a mre unifrm current density distributin, and the heat thus develped, ver the cable s crss sectin, cnsequently reducing the temperature at all pints and making the cable mre resistant t the abve mentined electrical and thermal stresses. The prpsed structure fr the cable is based n the nrmal extruded aluminum tube which cntains the ptical fibers and is embedded in armr aluminum cvered steel/aluminum ally wires. The s btained crss sectin is shwn in Figure 1, and its first theretical thermal analysis was presented in the 56 th IWCS [6]. Fr the electrmagnetic analysis, the results fr the mdified cable are cmpared t thse f three ther different cnfiguratins. 2. The cmmn prblems which ccur in OPGW cables When an OPGW is submitted t shrt circuit r lightning cnditins, heat is generated by Jule Effect in the metal layers. The heat prduces a fast increase in temperature in the aluminum tube befre the heat transfer frm the tube t the armr wires begins. Due t the skin effect the current ver the cnductr crss sectin is unevenly distributed, existing mstly at the surface f the external cnductrs [7]. This effect increases with frequency and is mre significant in magnetic materials due the larger values f their magnetic permeability. The increase in temperature caused by current flw, may nt nly cause serius damage t the tube and wires, but als t the ptical fibers. Therefre, the maximum temperature absrbed in the aluminum tube shuld be less than the allwable temperature in the cre with the ptical fibers [2]. The armr wires f the OPGW are usually made f steel, which may cause high magnetic hysteresis and eddy current lsses. T reduce magnetic lsses, nn magnetic materials such as aluminum are used [1]. Aluminum has a much smaller permeability than steel, and its thermal and electrical cnductivities are higher than thse f steel. Thus, inserting aluminum in the armr wires, it is expected that a mre unifrm current distributin can be achieved, Internatinal Wire & Cable Sympsium 64 Prceedings f the 57th IWCS

2 making it easier t transfer the heat between the tube that prtects the fibers and the armr. 3. The Mdified OPGW Prpsed The prpsed structure fr the cable is based n the nrmal extruded aluminum tube which cntains the ptical fibers and is embedded in armr aluminum cvered steel/aluminum ally wires. The s btained crss sectin is shwn in Figure 1, and the first theretical analysis has already been presented in the 56th IWCS [6]. Figure 1. Crss sectin gemetry f the prpsed OPGW A cable with the prpsed cnfiguratin was manufactured in rder t be tested under shrt circuit cnditins fr cmparisn with the calculated thermal results. Fr the electrmagnetic analysis, the three structures shwn in Figure 2 were cnsidered, and the numerical results fr these cnfiguratins are presented in the analysis. The dimensins shwn in Figure 2 are given in Table 1. The thickness f the aluminum cver is given by r a - r b. The physical parameters fr the structures are shwn in Table 2. In Figure 2(b) letter c stands fr the steel wires, and letter b fr the aluminum ally wires. Table 1. Dimensins f the analyzed structures Radius Value (mm) Descriptin R dielectric cre radius (inner aluminum tube radius) R uter aluminum tube radius R cable ttal radius r a armr wire radius r b armr wire radius withut the aluminum cver Table 2. Parameters f the OPGW analyzed Material ε r µ r Cnductivity (S/m) Silica Aluminum Steel / Electrmagnetic Analysis This sectin presents the results btained frm the numerical simulatins t analyze the current density distributin ver the crss-sectins f the fur different cnfiguratins shwn in Figures 1 and 2. The relative permeability f steel used in the simulatins is μ r =1,000 [7] fr Figures 3, 4, 5 and μ r =1, 000 and μ r = 280 [8] fr Figure 6. Figure 3 shws the current distributin fr the frequencies f 60 and 500 Hz, cmparing the results fr the prpsed structure (Figure 1) t thse fr the cable with alternate armr wires, cnsidering the radius path taken ver the aluminum wire. (a) (b) (c) Figure 2. Crss sectin gemetries f: (a) typical structure, (b) aluminum/steel alternate wires, (c) aluminum cvered steel wires Figure 3. Nrmalized current density versus radius f the prpsed structure and with alternate armr (ver the aluminum wire) fr f = 60 and 500 Hz Internatinal Wire & Cable Sympsium 65 Prceedings f the 57th IWCS

3 Fr the frequency f 60 Hz the current is almst cnstant bth fr the aluminum tube and the armr aluminum wire. Althugh layers 2 and 3 have the same cnductivity in this case, it is seen that the current density suffers significant variatin with increasing frequency where the skin effect is mre prnunced. Figures 4 and 5 shw cmparisns between the fur structures fr the frequencies f 60 and 500 Hz, respectively. The current densities are calculated in layer 3 fr the steel wires. when the frequency is increased t 500 Hz (Figure 5) the current distributin remains almst cnstant. The permeability f the steel wires is als a factr that causes a great variatin in the current distributin. Figure 6 shws the current density behavir (fr the steel wires in layer 3) fr the cases f μ r = 1,000 and μ r = 280. Figure 4. Nrmalized current density versus radius at f = 60 Hz fr the fur structures analyzed (ver the steel wires) Figure 5. Nrmalized current density versus radius at f = 500 Hz fr the fur structures analyzed (ver the steel wires) Fr the prpsed cnfiguratin and the ne with aluminum cvered steel armr wires a unifrm current density distributin was btained in the steel wires at the frequency f 60 Hz. Even Figure 6. Nrmalized current density versus radius fr structure prpsed fr f = 500 Hz 5. Thermal Analysis Fr the thermal analysis, tw cables with different cnfiguratins were tested under shrt circuit cnditins, and the test results were cmpared t the theretical results f the mdel presented in [6]. The first cable (cable A) is made f 12 aluminum cvered steel wires (ACSW) and the secnd (cable B) alternates 6 aluminum ally wires with 6 galvanized steel wires (AAW). Cable A was submitted t ten current tests f 15 ka each. The initial temperature befre each test was 50 C. Apprpriate thermcuples were fixed at pints lcated n the uter surface f the aluminum tube, and at tw pints lcated at the interface between tw adjacent ACSW. The measured temperatures f bth the aluminum tube and the ACSW are pltted in Figure 7. The figure als shws the predicted results btained frm an analytical slutin reprted in [6]. The analytical slutin is fitted against the measured temperature f the tube by adjusting a thermal cntact resistance parameter, as reprted in the mentined papers. The axial lad during the test was mnitred by and apprpriate lad cell. The cllected results are pltted in Figure 8. Instead f adjusting parameter Λ as made in the previews wrks mentined, the fitting parameter is ( hϕ ) = lim ( hϕ ), ϕ 0 where 2 h[w / m K ] is the heat transfer film cefficient referred t the cntact surface (strip) between the tube and the wires, and ϕ is the effective cntact angle as defined in (2007). The parameter Λ is shwn t be directly prprtinal t ( hϕ ). The Internatinal Wire & Cable Sympsium 66 Prceedings f the 57th IWCS

4 parameter ( hϕ ) is fitted against its adjusted discrete values with time, by the Bltzmann crrelatin expressed as ( hϕ ) = ( A1 A2 ) /[ 1+ exp(t t ) / Δt ] + A2, where A 1, A 2, and Δ t are cnstants. The experimental discrete values f ( hϕ ) as well as the fitting curve are pltted in Figure 9. As can be bserved in Figures 8 and 9, the greatest variatin f ( hϕ ) ccurs during the first tw secnds just after the current test applicatin perid. During this cling perid, the axial lad varies steeply frm its prelad value f 2,600 N t arund 1,000 N. The analytical slutin is able t describe the heat transfer f the cable nly in the perid f arund ten secnds, during which the cling phenmena can be cnsidered adiabatic. Figure 7. Plts f the experimental values f the temperature, and predicted values btained frm the analytical slutin reprted in [6] Figure 8. Plts f the experimental values f the cable axial lad Figure 9. Plts f experimental adjusted values f ( hϕ ), and Bltzmann crrelatin fitting Fr cable B the test was carried ut by ten applicatins f a test current f 12.3 ka. The initial temperature befre each test was 50 C. The experimental values as well as the predicted values f the cable temperatures are pltted in Figure 10. Fr this cable, the parameter ( hϕ ) refers t the cntact interface between the aluminum tube and the galvanized steel wires. The thermal cntact resistance fr this interface is much mre sensitive than the ne related t the interface between the aluminum tube and the AAW. The temperature f bth the AAW and the galvanized steel wires were measured by apprpriate thermcuples fixed at the uter cable radius. As seen frm Figure 10, the predicted wire temperatures are in disagreement with the experimental values. Hwever, it must be taken int accunt that the predicted temperatures are the average crss sectin temperatures f the wires, while the measured temperature are taken frm pints lcated at the external surface f the cable, where cling effects arise due t the cable scillatin in surrunding cl air. This may explain the reasn why the wire temperatures are lwer than the predicted nes. The axial lad measured during the test is pltted in Figure 11. As made fr cable A, the experimentally adjusted value f ( hϕ ) are fitted by the Bltzmann crrelatin and pltted in Figure 12. It can be seen by cmparing Figures 10 and 11 that a better interface cntact cnductance is fund fr cable B, fr which ( hϕ ) decreases less intensively in cmparisn t the case f cable A. Similar results are fund fr the variatin f the axial lad with time. The better thermal cntact fund fr cable B may be explained by the fact that the axial lad fr this cable is almst ttally recvered during the first tw secnds after the current applicatin perid. Since the axial lad reflects the interface cntact pressure, n which the thermal cntact surface depends, a less effective thermal cntact is expected fr cable A. These results suggest that there is a crrelatin between the variatin f the axial lad and the variatin f ( hϕ ) with time, as can be bserved by cmparing Figures 8 and 9 with Figures 11 and 12. Internatinal Wire & Cable Sympsium 67 Prceedings f the 57th IWCS

5 Figure 10. Plts f the experimental values f the temperature, and predicted values btained frm the analytical slutin reprted in [6] Figure 11. Plts f the experimental values f the cable axial lad Figure 12. Plts f experimental adjusted values f ( hϕ ), and Bltzmann crrelatin fitting 6. Cnclusins This paper presented an analysis f a mdified OPGW, designed t btain a better heat transfer perfrmance and thus be capable f withstanding the harsh cnditins f shrt circuit and lightning. Cmparing the results btained fr the prpsed structure t thse f the cnfiguratin with alternate armr wires, it is seen that in the first case the current distributin is mre cncentrated in the aluminum tube than in the secnd case, reducing the heat in the armr. At the interface between the aluminum tube and the aluminum armr wires there is a current density discntinuity due t the small cntact area. In this area there is a large cncentratin f electrmagnetic fields. Thrugh the analysis f the fur structures it is pssible t see that thse withut aluminum cvered steel have a larger cncentratin f current density in the armr wires. The heat transfer mdel reprted in previus wrks by the authrs [6] was used t determine the thermal cntact cnductance at the interface cntact surface between the aluminum tubes and the wires. The analytical slutin is apprpriate t characterize the heat transfer f cables submitted t shrt circuit tests and, therefre, t design the type f cables studied here, by cnsidering the effect f the therm-physical prperties, as well as the materials temperature limits. 7. References [1] G. J. Anders, Rating f Electric Pwer Cables: ampacity cmputatins fr transmissin, distributin, and industrial applicatins, IEEE Press Pwer Engineering Series, New Yrk (1997). [2] K. Ryuz, Y. Kji, T. A. Schéhade, V. Lászi and G. Ottó, Develpment f an Aplicatin Prgram t Calculate Shrt- Circuit Temperature Rise in OPGW, in: Furukawa Review,N. 18 (1999). [3] K. Q. da Csta, V. Dmitriev, J. T. Pinh, S. Clle, L. Gnzalez, M. A. Andrade, J. C. V. da Silva, and M. Bedia, Analytical Mdel fr the Calculatin f Current Density Distributins ver the Crss-Sectin f a Multi-Cnductr Cable, IWCS Internatinal Wire and Cable Sympsium, Prvidence (2006). [4] K. Q. da Csta, V. Dmitriev, J. T. Pinh, L. Gnzalez, S. Clle, M. A. Andrade, J. C. V. da Silva and M. Bedia, Numerical Calculatin f Current Density Distributins ver Crss-Sectin f a OPGW Cable, 16 th Internatinal Cnference n the Cmputatin f the Electrmagnetic Fields, Aachen, Germany (2007). [5] J. T. Pinh, V. Dmitriev, K. Q. da Csta, L. Gnzalez, S. Clle, M. A. Andrade, J. C. V. da Silva and M. Bedia, Theretical Analysis f Current Density Distributins ver the Crss-Sectin f a Mdified OPGW Cable t Reduce the Skin Effect Area, IWCS Internatinal Wire and Cable Sympsium, Lake Buena Vista (2007). [6] S. Clle, M. A. Andrade, J. T. Pinh, J. C. V. da Silva, M. Bedia, Carls E. Veiga and J. N. Scussel, Temperature Respnse f OPGW with Armred Aluminum Cvered Steel Wires Aluminum Allys Wires Submitted t Shrt- Circuit, IWCS Internatinal Wire and Cable Sympsium, Lake Buena Vista (2007). Internatinal Wire & Cable Sympsium 68 Prceedings f the 57th IWCS

[7] Z. Mir, J. Franc and T. Igr, Skin Effect Impact n Current Density Distributin in OPGW Cables, in: Electrtechnical Review (2003). [8] Z. Mir and T.

Bawler, Frequency Dependence f Relative Permeability in Steel, in: Review f Quantitative Nndestructive Evaluatin, Vl. 25, American Institute f Physics, USA, (2006). 8.

degree in electrical engineering frm the Universidade Federal d Pará (Brazil) in 1977, the M.Sc.

degree in electrical engineering frm the Rheinisch-Westfälische Technische Hchschule Aachen (Germany) in 1990.

research grup n energy alternatives and micrwave applicatins. His research interests are centered in electrmagnetics and in renewable energy surces, especially slar and wind.

Pinh is ad hc advisr fr several institutins in Brazil, member f varius scientific scieties, and presently president f the Internatinal Slar Energy Sciety - Brazilian Sectin Victr Dmitriev was brn

The fields f his scientific interest are micrwave, millimeter wave and ptic cmpnents, applicatin f grup thery t electrmagnetic prblems, cmplex media, nanphtnics, and mathematical methds f

degree in electrical engineering frm the Federal University f Pará in March 2008. She is nw a dctr student at UFPA. Prf.

Engineering in 1976 COPPE / University f Ri de Janeir.

Marcel de Arauj Andrade was brn in Flrianóplis SC Brazil in 1965. He graduated in Mechanical Engineer frm Universidade Federal de Santa Catarina in 1988.

6 [7] Z. Mir, J. Franc and T. Igr, Skin Effect Impact n Current Density Distributin in OPGW Cables, in: Electrtechnical Review (2003). [8] Z. Mir and T. Igr, Determinatin f Current and Temperature Distributin in Overhead Cnductrs by Using Electrmagnetic-Field Analysis Tls, in: IEEE Transactins n Pwer Delivery, Vl. 21, N.3 (2006). [9] N. Bawler, Frequency Dependence f Relative Permeability in Steel, in: Review f Quantitative Nndestructive Evaluatin, Vl. 25, American Institute f Physics, USA, (2006). 8. Pictures f Authrs Jã Tavares Pinh was brn in Belém, Pará, Brazil, n August 22, He received the B.Sc. degree in electrical engineering frm the Universidade Federal d Pará (Brazil) in 1977, the M.Sc. degree in electrical engineering frm the Pntifícia Universidade Católica d Ri de Janeir (Brazil) in 1984, and the Dr.-Ing. degree in electrical engineering frm the Rheinisch-Westfälische Technische Hchschule Aachen (Germany) in He has been with the Department f Electrical Engineering f the Universidade Federal d Pará since 1978, has wrked as an assistant at the RWTH Aachen, and is presently a full prfessr and leader f a research grup n energy alternatives and micrwave applicatins. His research interests are centered in electrmagnetics and in renewable energy surces, especially slar and wind. In these areas he has supervised many graduate and undergraduate wrks and published several papers. Prf. Pinh is ad hc advisr fr several institutins in Brazil, member f varius scientific scieties, and presently president f the Internatinal Slar Energy Sciety - Brazilian Sectin Victr Dmitriev was brn in Russia, in Currently, he is a prfessr at the Federal University f Pará, Belám, Brazil. Dr. Victr Dmitriev has mre than 120 papers in scientific jurnals, several bks and patents. The fields f his scientific interest are micrwave, millimeter wave and ptic cmpnents, applicatin f grup thery t electrmagnetic prblems, cmplex media, nanphtnics, and mathematical methds f electrmagnetic thery. Luciana Pereira Gnzalez was brn in Belém, Pará, Brazil in She graduated in Electrical Engineering in May 2006 and received the M.Sc. degree in electrical engineering frm the Federal University f Pará in March She is nw a dctr student at UFPA. Prf. Sergi Clle received his Mechanical Engineer degree in 1970 frm the UFSC, Master f Science in Mechanical Engineering in 1972 frm COPPE / University f Ri de Janeir, and Dctr f Science in Mechanical Engineering in 1976 COPPE / University f Ri de Janeir. He is Prfessr f Thermdynamics, Heat Transfer and Slar Energy at the Department f Mechanical Engineering f UFSC since 1974, and presently head f LEPTEN. Marcel de Arauj Andrade was brn in Flrianóplis SC Brazil in He graduated in Mechanical Engineer frm Universidade Federal de Santa Catarina in He jined Prysmian Telecmunicações Cabs e Sistemas d Brasil in 1988 and is currently in charge f Cmercial and R&D Directin. Jã Carls Vieira da Silva was brn in Sã Paul SP Brazil in He graduated in Physics frm Universidade de Sã Paul in 1982 and Electrical Engineering frm Faculdade de Engenharia de Srcaba in He jined Prysmian Telecmunicações Cabs e Sistemas d Brasil in 1977 and is currently in charge f Prduct Engineering Department. Maur Bedia Jr. was brn in Sã Paul SP Brazil in He graduated in Mechanical Engineer frm Faculdade Santa Cecília in He jined Prysmian Telecmunicações Cabs e Sistemas d Brasil in 1989 and is currently respnsible fr OPGW and ADSS cable develpment. Juli Nelsn Scussel was brn in Trevis, Santa Catarina, Brazil in He graduated in Mechanical Engineer frm Universidade Federal de Santa Catarina in 1997 and has an M.Sc. degree in Industrial and Scientific Metrlgy frm Universidade Federal de Santa Catarina in He is presently researcher f LEPTEN. Internatinal Wire & Cable Sympsium 69 Prceedings f the 57th IWCS

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