1 SUMMARY 2 INTRODUCTION. By Wim Boone and Christiaan Sonderen, DNV GL

Transcription

1 Copper in comparison to aminim as common materia in condctors of LV and MV power cabes; properties and reated decision framework on how the condctor materia is being seected By Wim Boone and Christiaan Sonderen, DNV GL SUMMARY The Eropean Copper Institte (ECI) reqested DNVKEMA, now part of DNV GL, to investigate the position of copper verss aminim in the appication of LV and MV cabe condctors, in particar paying attention to the decision mode how to seect copper or aminim: The iteratre srvey made cear that there seems to be more faire mechanisms reated to aminim condctor than to copper condctor. The major mechanisms identified are: The chemica reaction between aminim and water The chemica reaction between aminim and oxygen The thermo-mechanica behavior of aminim. The decision mode shows price as a dominant factor to the advantage of aminim. Other, ess dominating factors, ike connector probems, ease of instaation of joints and repair are to the advantage of copper, whie ower specific weight and the compatibiity with other cabes are to the advantage of aminim. Srprisingy the factors radia dimensions, environmenta concerns and costs of corrective maintenance scored reativey ow in the decision frame work. In short, it is fair to say that for both LV and MV cabe circits, aminim condctor cabe pays a dominating roe becase of the cost advantage. However, the technica advantages of copper are obvios, and copper can contine to pay a roe in cabe appications where these advantages weigh the most. The tiity indstry is crrenty too mch focsed on initia costs and insfficienty aware of the benefits of copper. The move from copper to aminim may affect technica performance of distribtion networks as we as tota cost of ownership. The impact of condctor choice on technica and financia performance of eectricity networks merits to be better nderstood. 2 INTRODUCTION Nowadays there is discssion with respect to the seection of copper or aminim as common condctor materias in power cabes [3], [4], [5]. Next to price differences, each materia has positive and negative characteristics that affect their se in varios appications. Originay copper was the ony condctor materia sed, ater aminim was introdced as a condctor materia as we. Some tiities are in favor of copper, some tiities are increasingy sing aminim. Certain properties of aminim are favorabe above copper for certain appications. These appications reqire for instance: a ighter system in aircraft appications where power to weight ratios are critica. KEMA Nederand B.V. Utrechtseweg 30, 682 AR Arnhem P.O. Box 9035, 6800 ET Arnhem The Netherands T F [email protected] Registered Arnhem DNV GL PMT/POL DNG GL paper.docx

2 Page 2 of 3 Aternativey, when the physica size of the cabe is a imiting isse, for instance in dcts, copper is a better choice than aminim, becase aminim condctor wi have a cross-sectiona of 64 % arger than copper for the same crrent carrying capacity. By reqest of the Eropean Copper Institte (ECI), DNV KEMA, now part of DNV GL was asked to investigate on what gronds distribtion tiities decide to se copper or aminim condctors in LV and MV cabe networks. A qestionnaire was prepared that was sent to abot 00 distribtion tiities in 25 contries, to obtain accrate and reiabe written information. The qestionnaire consisted of three parts, of which ony the third part on the decision mode how to seect copper or aminim wi be deat with in this paper. After giving smmarized information on the typica properties of copper and aminim condctors in chapter 3 and information on faire mechanisms reated to condctor materia in chapter 4, the rests of the qestionnaire are given in chapter 5. Finay evaation and concsions are described in respectivey chapter 6 and 7, foowed by a ist of references in chapter 8. 3 CONDUCTORS USED IN LV AND MV POWER CABLE NETWORKS 3. Avaiabe condctors for LV and MV cabes The internationa cabe indstry provides cabes with both stranded copper and stranded aminim condctors, say in rond constrction (fig. ), bt aso sector shaped constrctions. Some manfactrers aso provide soid aminim condctors (fig. 2), bt ony a few deiver p to.600 mm 2 and arger. Figre Copper and aminim stranded condctors Figre 2 Aminim soid condctor Specificay for LV cabes stranded and soid aminim and stranded copper condctors are provided in rond and sector shaped constrction. In [0] the nomina cross-sectiona areas, in the range of 0.5 mm 2 to mm 2 are specified. These condctors incde soid and stranded, rond and sector shaped copper and aminim condctors in cabes for fixed instaations and fexibe copper condctors. DNV GL PMT/POL

3 Page 3 of Typica differences between Copper and Aminim As the density of aminim is abot one third of that of copper, for eqa condctance the weight of the aminim condctor materia is amost haved. However the cross-sectiona area has to be increased by a factor of.6 and this means extra sage of insating materia, sheathing materia and armoring. Becase of the smaer cross-section of copper condctor cabes compared with aminim condctor cabes, copper condctor cabes can be stored for a onger ength on a cabe ree or in a cabe ship in case of sbmarine cabe, resting in the need of fewer joints. It is sti worth recaing that copper condctor cabe is more dctie and ess ssceptibe to eectrica contact probems and ths offers a greater margin of safety than a corresponding aminim condctor cabe. De to its smaer crosssection, the copper cabe wi aso be easier to insta as the stiffness of the cabe depends on the sqare of the cross-sectiona area and ths on the forth power of the diameter. It is aso possibe to get very sma stranded copper cabe; stranded aminim cabe is ony avaiabe at nomina cross-sectiona areas of at east 0 mm 2 and the individa strands are sti very thick compared to those in the eqivaent sized copper cabe. For technica reasons mainy reated to the degree of eongation, so caed "finey stranded" and "extra finey stranded" condctors are ony avaiabe in Copper (0.5 6 mm 2 ). Another important piece of information to consider is the fact that Copper cabe is most commony sed for connecting offshore wind farms. This is becase the cabe needs to be heavy to provide a more stabe strctre in the soi. Frthermore, as mentioned before, copper condctor cabes have smaer radia size. Finay at ocations where the cabes are bent to connect to the wind farm strctre, copper is preferred de to its fexibiity and ths its workabiity. The option of aoying materias may improve mechanica properties of aminim. Aoy 350 has a arge coefficient of therma expansion, a ssceptibiity to bending and creep faires, a high rate of oxidation and vnerabiity to gavanic corrosion. These concerns are minimized with the se of 8000 series, proper eectrica connectors, proper instaation and appropriate connecting methods. However as the se of aoys has not an obvios appication for insated cabes, becase of the condctivity penaty, aminim and copper are both sed in insated cabes at high prity grade. Copper and aminim are both recycabe, to be sed as condcting materias in cabes again, In genera copper condctors wi be more pre than aminim condctors, however even assming that both materias wi contain other eements, according to the meta whee [6] recycing of copper deivers mosty recoverabe materias, as for recycing of aminim amost a of the other eements cannot be economicay recovered. This wi rest in a ot of scrap materia when recycing aminim and besides making the recycing process for copper more economicay attractive than for aminim. Typica comparative properties of aminim reative to copper (assmed vae is 00) are isted in Tabe [8]. DNV GL PMT/POL

4 Page 4 of 3 Tabe : Aminim vs Copper comparative materia properties in the pre state Materia Properties Comparative Vaes Copper Aminim Eectrica resistivity Density Weight/nit resistance Diameter/nit resistance Eastic mods Hardness Utimate tensie stress Meting point 00 6 Stress fatige endrance imit Therma resistivity Corrosiveness ) 2) Therma expansion ) Copper is resistant to most organic chemicas 2) Aminim may corrode qicky 4 FAILURE MECHANISMS RELATED TO CONDUCTOR 4. Genera Most of the ageing mechanisms in cabes are directy reated to insation faire as this is the most serios threat in the ife of the cabe. The stresses acting on cabes may be cassified in therma, eectrica, mechanica and chemica or a combination of the aforementioned. Ageing wi graday rest in a owering of the eectric strength of the insation and if a critica imit is passed into the sitation of faire. The ageing mechanisms affecting cabe condctors generay deveop more sowy and are ess ikey to occr than insation faires that accont for the majority of cabe faires. Condctor faire is very rare in MV power cabes where the wires are of arge diameter. In LV cabes, condctors are physicay smaer diameter wires and can occasionay break from meta fatige de to ong term exposre to vibration or excessive handing and termination. Aminim condctor cabes do have more insation than the comparabe copper cabe. One cod arge that more insation vome impies a higher risk of faire, as the nmber of dangeros defects increases with insation vome. On the other hand a arger diameter aso impies a better cooing, redcing the temperatre and therefore the risk of faire. As ong as statistics do not prove a significant difference in faire behavior between copper condctor cabe and aminim condctor cabe it is not jstified to do any reiabe prediction on the faire risk based on the above mentioned phenomena. DNV GL PMT/POL

5 Page 5 of 3 In the ageing of joints, the connector pays an important roe. The connector that joins the condctors within a joint can be vnerabe to ageing and degradation mechanisms sch as vibration, mechanica stress and therma-mechanica cycing. These mechanisms can rest in meta fatige of the condctors and/or oosening of the connector. Ingress of moistre into the interior can case corrosion and formation of oxides at the connector. This can case increased eectrica resistance and increased heating. 4.2 Faire mechanisms reated to aminim condctor Specificay for aminim cabe condctor cabes, three main isses have been coected which can practicay ead to faires: Chemica reaction between water and aminim []. If water comes into contact with aminim a chemica reaction happens resting in the deveopment of hydrogen at reativey high pressre to magnitdes which are impossibe to contain within existing joints or connectors. Additionay, increased partia discharge (PD) activity can occr de to interface contamination. This may trn to srface discharges (tracking) and sbseqent faire. At aboratory scae sch process has been sccessfy demonstrated. The most effective answer to gas generation probems is to prevent water from entering the power condctor system, by appying radia and ongitdina watertight protection methods. However in many cabes sch methods are not present. Athogh this faire mechanism ooks rather threatening, there was no confirmation avaiabe from tiities abot this faire mechanism ever happening dring operation. Oxide ayer on aminim and corrosion. Aminim oxidizes readiy when exposed to oxygen forming a thermodynamicay and chemicay stabe sitation. This insating oxide ayer is very thin (nanometre scae), however if not propery removed before appying a connector to connect wires to each other, an extra resistance wi be created resting in overheating. Aminim connectors reqire greater care de to increased therma instabiity compared to copper, when the protective oxide ayer forms, a process which occrs natray. In addition, when aminim cabes are instaed in sois having a ph otside the range (non-draining cay-organic mcks etc.), the oxide ayer which wi form natray is nstabe and wi case corrosion of the meta. Gavanic corrosion is more important for aminim when it comes into contact in an eectroyte with a more cathoic meta ike Fe, Ni, Pb, Sb, C etc. dring a connection etc. and it is more ssceptibe to corrosion [4]. Copper is according to the arrangement of eectrochemica potentia mch more precios than aminim and wi therefor ony corrode when it is in contact with precios metas ike Ni, Ag, Pt. In [2] the rests are presented of the characterization of MV extrded cabes with a corroded aminim condctor and aged nder varios simated fied conditions. The rests indicated that the presence of water and corroded aminim in the condctor strands decreases cabe performance. It has to be borne in mind that specia ceaning techniqe and improved connector designs rested in acceptabe sotions. Thermo-mechanica faire de to the mechanica properties of aminim, in particar in case of soid Aminim condctors.[9] The therma inear coefficient of expansion for aminim is 36 % greater than that of copper. If the proper connector is not sed, high stress cod occr de to neven growth between the condctors and the connectors dring therma cycing. In case of soid condctors high forces are generated in the joints for high oads becase the expansion is amost entirey in the ongitdina direction. Creep, DNV GL PMT/POL

6 Page 6 of 3 the continos deformation nder stress, is mch higher than for copper. This fact was not taken into accont in instaation techniqes or termination devices and this contribted to heating isses at the connections. This isse has been mitigated with the se of different series of aminim aoys (for instance 370, 99,7% aminim or 350, 99,5% aminim) and sitabe connection methods and connectors. As described in [9], aboratory tests as we as theoretica cacations are carried ot to expain freqent joint faires de to high cycic oads. Aminim condctors, in particar soid aminim condctors are responsibe for high eve of mechanica forces if the condctor cannot expand ongitdinay and radiay, resting in a joint faire, say via a oosening of: the connector or via sideward moving of the condctor throgh the insation. 4.3 Faire mechanisms reated to Copper For copper condctor cabes no cear threatening faire mechanisms cod be fond that are reated to copper condctor. However copper does corrode in the presence of water or moistre forming a condctive oxide ayer and then to a ayer caed "patina". These formations increase its resistance at the connector points. This can ead to overheating and finay faire of the connection. In the presence of sphr dioxide the transition from the oxide ayer to the so caed "patina" is enhanced. Copper is aso vnerabe when bried in sois, to arge qantities of organic acids, ammonia and cinder fis. It mst be mentioned that cay sand, grave, oam, and chak hardy possess the combination of properties that promote corrosion of copper in soi [4]. We beieve that for insated copper condctors as in cabes, if propery instaed and connected in joints, the possibiity of faire de to oxidation or corrosion is minima compared to the case of aminim condctor for the predicted ifetime of the cabe. 5 UTILITIES' ANSWER TO QUESTIONNAIRE REGARDING LV AND MV POWER CABLE CONDUCTORS 5. Introdction This report is based on 6 qestionnaires competed from distribtion tiities originating from the foowing contries:. Begim 2. Brazi 3. Brazi 2 4. Denmark 5. Denmark 2 6. Germany 7. Netherands 8. Poand 9. Soth Africa 0. Soth Africa 2. Spain 2. Switzerand 3. Thaiand 4. Trkey 5. Netherands 6. Mexico Athogh the nmber of competed qestionnaires is rather sma, the geographica spread is satisfactory: 9 from Erope, 2 from Africa, 2 from Asia and 3 from America. DNV GL PMT/POL

7 Page 7 of Condctor seection This part of the qestionnaire (Qestionnaire part III) deas with information on how tiities make their decision in seecting condctors: copper or aminim. The foowing factors were seected, to be considered as important seection criteria as possibe answers in the qestionnaire:. Price per meter of cabe 2. Radia size 3. Weight per meter of cabe 4. Mechanica properties 5. Ease of accessory instaation 6. Ease of repair 7. Cost of corrective maintenance (repair after faire) 8. Company standard or company procedres 9. Compatibiity with existing cabes in network 0. Environmenta concern (osses). Expected probems with connectors 2. Any other factor. In the qestionnaire for each factor two comns are present, one for LV and one for MV networks. The participants were asked to rate the importance of each factor concerned from to 5, where refers to a rating of east importance and 5 to a rating of highest importance. Frthermore the participants were asked to indicate per factor the preferred condctor materia, copper or aminim. Next to the specified factors there was at the end a free row where the participant cod enter a new factor not specified yet. In tabe 2 the rests are given of tota scores for LV cabe systems of the participants invoved as in tabe 3 the rests for MV cabes are reported. In both tabes the participants are represented from B- B6 horizontay (4 participants as B8 and B5 did not generate reevant information), whie the decision factors are represented verticay form -2. In two vertica comns (TA and TC) the sm is given of tota scores for the different factors for respectivey Aminim and Copper. Tabe 2 LV scores given for 2 factors by 4 tiity participants B B2 B3 B4 B5 B6 B7 B9 B 0 B B 2 B3 B4 B 6 T A T C 5A 5A 5A 5A 5A 5A 2C 5A 2C 4C 5A C 3C -- A A 2A 3A 2C 3C 3A C 4C 2C 2C A C 2A A 2A C 3C 3A 3C 2C 2C 2A A 3C -- 3A 3A 4C 4C 3A 4C 4C 2C C C -- A 4C 4C C 3C 4C 3C C C -- A C 2A 4C C 3C 2C C -- A na --A 2A 4C 3C 3C 22 DNV GL PMT/POL

8 Page 8 of 3 B B2 B3 B4 B5 B6 B7 B9 B 0 B B 2 B3 B4 B 6 T A T C 8 5A 2A 5A 5A C A C 5A 2A A 5A 3C 3C 4C A /A -- A A 3A Na 3C 3C 3C C -- A A 3A 4C 4C C 4C 4C 3C ) De to congestion in ndergrond faciities, space for UG rote is imited Tabe 3 MV scores given for 2 factors by 4 tiity participants B B2 B3 B4 B5 B6 B7 B9 B 0 B B2 B3 B 4 B 6 TA TC 5A 5A 5A 5A 5A 5A 2C 2C 5A 5A C 3C -- A A 2A 3A 3C 3A 2C 4C 2C 3C A C 2A A 2A C 3C 3A 2C 2C 3A A 3C -- 3A 3A 4C 3A 3C 4C 2C 3C C C -- A 4C 4C C 3C 5A 3C C C -- A C 2A 4C C 3C 2C C -- A na -- 2A 4C 3C 5A A 2A 5A 5A 4C C 5A A C 5A 2A A ; 5A 4C 4C 5A A /A -- A 3A 3A Na 3C 3A 3C 23 2 DNV GL PMT/POL

9 Page 9 of 3 3C -- A A 3A 3C C 4C 5A 3C ) Fireproof 2) De to congestion in ndergrond faciities, space for UG rotes imited As can be seen from tabes 6 and 7 some factors give a high score (for instance factor for aminim, some give a ow score (for instance factor for copper). In tabe 4 and 5 the order of tota scores of factors -, from high to ow vaes, for aminim and copper cabes are given for both LV and MV cabe systems. It tes what vae is given to a certain factor and by separating between aminim and copper the decision process to seect copper or aminim becomes visibe in decreasing order of importance. Tabe 4 LV cabes, order of tota scores of factors from high to ow C A. Company standard, 26 Price, Mechanica, 26 Company standard, Connectors, 25 Compatibiity, Compatibiity, 24 Weight, 2 5. Environment, 24 Mechanica, 8 6. Repair, 23 Environmenta, 8 7. Corrective maintenance., 22 Accessory instaation, 3 8. Accessory instaation,22 Connectors, 3 9. Radia size, 8 Corrective maintenance, 0. Price, 8 Repair,. Weight, 2 Radia size, 0 DNV GL PMT/POL

10 Page 0 of 3 Tabe 5 MV, cabes, order of tota scores of factors from high to ow C A. Mechanica, 24 Price, Connector, 24 Company standards, 3 3. Radia size, 23 Compatibiity,27 4. Repair, 23 Mechanica, Accessory insta., 22 Weight, 8 6. Compatibiity, 22 Accessory, 8 7. Environmenta, 2 Environmenta, 8 8. Company standards,20 Connector, 8 9. Corrective maintenance, 9 Corrective maintenance, 6 0. Price, 4 Repair,. Weight, 4 Radia size, 0 6 EVALUATION OF RESULTS The differences in the decision to choose copper verss aminim are noticeabe. For aminim for both LV and MV cabes the dominating factor is price (score 44 for LV and score 48 for MV cabes). The other factors for aminim score significanty ower in vae. For copper there is not sch a dominating factor, bt rather a combination of factors. The other remarkabe fact is that there exists a great simiarity in decision mode between LV and MV aminim condctor cabes. The order of decision factors is for LV and MV cabes amost identica, as for copper condctor cabes there are sti some difference. It is diffict to find a satisfactory expanation. It cod be that for aminim the decision mode is more strctred and more company controed than for copper. On the other hand the impression is made that the decision to seect aminim is more reated with the ower price of aminim than with technica argments. When smmarizing the rests with the three highest scores from tabe 8 (LV cabes) we notice for copper condctor cabes the foowing factors: Company standard/company re 2 Mechanica properties 3 Expected probems with connectors. DNV GL PMT/POL

11 Page of 3 For LV aminim condctor cabes with the three highest scores we fond the foowing factors: Price per meter cabe 2 Company standard/company res 3 Compatibiity with existing network. From tabe 9, for MV cabes, we fond for copper condctor cabes the foowing highest scores: Mechanica properties 2 Expected probems with connectors 3 Radia size. For MV aminim condctor cabes we fond: Price 2 Company standards/company res 3 Compatibiity with existing network. When smmarizing the rests for the owest scores we notice for LV as we as for MV cabes for copper the foowing factors: Price 2 Weight. And for aminim: Easy repair 2 Radia size. Focsing on the technica reasons to seect copper above aminim the foowing points can be isted: Mechanica properties are considered to be better Probems with connectors in combination with aminim condctors seem to be in the advantage of copper condctors Instaation of accessories and repair aso seem to be topics that are advantageos for copper condctors The smaer radia size is an advantage. When considering the opposite approach, to ist technica reasons to seect aminim above copper, the foowing can be concded: The ower specific weight of Aminim is a point of attention The compatibiity with existing network. The isse of environmenta concern does not score high, both for aminim and copper. Athogh copper has a higher specific condctivity than aminim, in practica sitations condctors of both materias have the same condctivity and conseqenty the same osses, becase different cross sections are seected. DNV GL PMT/POL

12 Page 2 of 3 7 CONCLUSIONS In this report attention is being paid to copper verss aminim in reation to the decision mode. A nmber of faire mechanisms in particar reated to aminim cod be identified, as for copper no cear faire mechanism cod be fond. Athogh this report is not deaing with faire data, the reported faire mechanisms are of importance as they wi infence the decision mode. For that reason they are briefy smmarized beow: Chemica reaction between aminim and water, resting in the deveopment of high pressre hydrogen and reated joint faires, however tiities cod not confirm this mechanism from their practica experience Chemica reaction between aminim and oxygen, resting in high transition resistances in joints connectors and reated joint faire, however specia measres can bring this mechanism nder contro Thermo mechanica behavior of aminim de to significant higher coefficient of expansion and reated mechanica faire, however the practica experience is controversia. The present faire statistics do discriminate between XLPE and paper insation. However they do not discriminate between copper and aminim condctor, so it is impossibe to concde from the faire statistics any correation between condctor materia and faire behavior. Investigation of the decision mode, how to seect copper or aminim earned that there is one factor, the significant ower price of aminim, which pays a dominating roe in the decision process. The other factors seem to be of esser importance. Factors that benefit the seection of copper condctors are: Probems with connectors in aminim condctor cabes Easiness in instaation of joints and repair Mechanica properties Radia size. For aminim condctor cabes the foowing isses showed a reativey high score: Lower weight per meter cabe Compatibiity with existing cabes. It is fair to say that for both LV and MV cabe circits, aminim condctor cabe pays a dominating roe becase of its cost advantage. However, the technica advantages of copper are obvios, and copper can contine to pay a roe in cabe appications where these advantages weigh the most. The tiity indstry is crrenty too mch focsed on initia costs and insfficienty aware of the benefits of copper. The move from copper to aminim may affect technica performance of distribtion networks as we as tota cost of ownership. The impact of condctor choice on technica and financia performance of eectricity networks merits to be better nderstood. DNV GL PMT/POL

13 Page 3 of 3 8 REFERENCES [] R. Bartnikas, K. Srivastava, "Power and Commnication Cabes: Theory and Appications", IEEE Press, John Wiey & Sons Inc. Pbication, ISBN , [2] Storm Prodcts Company, "Cabe Interconnect System Design and Component Seection Mana", Section A: Condctors. [3] R. Coombs, Bateman, "Comparison of Aminim Vs Copper Power Cabes for Use in Indstria Appications", Instaations and Contractors, Jy 200. [4] A. Mak, P.Eng. Senior Fied Appications Engineer, "Corrosion of Stee, Aminim and Copper in Eectrica Appications", Acan Cabe, [5] J.B. Dixon, D. T. Rooney, N. T. Casteo, "Meta Migration Faires in a Hybrid Device: Interaction of Package Materias, Process residas and Ambient Gases", Oneida Research Services, Inc., ISHM Proceedings, San fransisco, CA, 992 [6] M. Viaran, R. Lofaro, "Essentia Eements of an Eectric Cabe Condition Monitoring Program", United States Ncear Regatory Commission (U.S.NRC), NUREG/GR-7000, BNL-NUREG , Janary 202. [7] L. Pryor, R. Schobohm, B. Browne, "A Comparison of Aminim vs. Copper as Used in Eectrica Eqipment", Sr. Specification Engineers, GE Consmer & Indstria [8] G. F. Moore, "Eectric Cabes Handbook", 3 rd Edition, BICC Cabes, Backwe Science Ltd., ISBN , 997 [9] R. Bodega eo, Seecting the optimized condctor for design, Jicabe 20 B.0. [0] IEC Condctors of insated cabes [] G.J.Lzzi Gass pressre bid p in Aminim condctor cabe, IEEE Trans.on PAS,Vo,PAS-0, No 6 Jne 982 [2] S.Pisso, J. Cote, eo. Infence of corroded condctors on the performance of MV extrded cabes, Jicabe,03 [3] R.Coombs, Comparison of Aminim vs Copper power cabes for se in indstria instaations, Jy 200, Vector [4] L.Pryor eo,a comparison of Aminim vs Copper as sed in eectrica eqipment, GE Indstria sotions 200 [5] Aminim Wire, WIKEDIA September 200 [6] Meta Recycing Opportnities, Limits, Infrastrctre UNEP Report 203 DNV GL PMT/POL