HVDC Madeira Transmission System – Planning Development and ...

21, rue d’Artois, F-75008 PARIS B4_306_2010 CIGRE 2010http : //www.cigre.orgHVDC Madeira Transmission System – Planning Development and Final DesignP.C.V. ESMERALDO (*) E.M.A. ARAÚJO D.S. CARVALHO JR.EPE – EMPRESA DE PESQUISA ENERGÉTICABRAZILSUMMARYThis paper presents the planning development and final design of the 2,375 km Madeira TransmissionSystem, to interconnect Santo Antônio and Jirau hydroelectric plants, 6,450 MW, located at theAmazon region, far Northwest of Brazil, to the main load center.Several alternatives for different transmission technologies were investigated during the feasibilitystudies, considering steady-state operation analyses, dynamic performance, and economic evaluation.The final conclusion of those studies recommended the best solution concerning technical andeconomic performance, which was a transmission system with two HVDC + 600 kV bipoles (3,150MW each) and two back-to-back devices (400 MW each) for local loads connection. In order toincrease competition in the bidding process, the Brazilian authority recommended that at least threedifferent technical alternatives should be taken into account. In addition to the previous DCAlternative, the feasibility analysis recommended a Hybrid Alternative, with one DC bipole (3150MW, + 600 kV) and two AC 500 kV parallel compensated lines, and an AC Alternative, with threeAC 765 kV parallel compensated lines.All three alternatives were submitted to complementary and detailed analysis including transientsswitching simulations, power recovery and blocking of DC bipole. One of the main concerns was tosimulate the accelerating torque submitted to the Madeira bulb type turbo generators. These resultsrecommended discarding AC Alternative and adopting DC and Hybrid alternatives which competed inan auction resulting with the DC Alternative as the winner with annual revenues smaller than theestablished ceiling. As permitted in the bidding process, the final design solution proposed to beimplemented by the new owners of Madeira Transmission System encompasses modification tooptimize the whole new system. In conclusion, the Madeira Transmission System final design reflectsa criterion and efficient process of planning.KEYWORDSHVDC Madeira Transmission System, Transmission alternatives, Transmission system auction,Planning development and final design, Bulb generator, Switching surge, Dynamic Analysis.(*) paulo.esmeraldo@epe.gov.br

1 INTRODUCTIONMadeira river hydroelectric plant projects, Santo Antônio and Jirau, generating together 6,450 MW,are the first big hydro plants at the Amazon region, far Northwest of Brazil, near the border withBolivia and Peru. The Brazilian power system interconnects 98% of the existing load, whichencompasses now local load at Porto Velho area, site of Madeira. But local load is very small, andMadeira site distance 2,375 from the main loads located in the Southeast. The generation project was,then, conceived to supply local load and the energy surplus to be transmitted to a long distance. Theamount of energy and the distance, crossing different regions of the country, made such a transmissionsystem very challenging and unique to be planned and implemented.The transmission planning process in Brazil encompasses a technical and economic study to establisha reference solution, an opened and public auction and a final design to be implemented by the newowners. It initiates with a first selection of alternatives considering a broad range of conceptions interms of technologies, routes, new substations, and points of connection to the existing network.The feasibility studies starts with steady-state analysis, dynamics performance and economicsevaluation of these alternatives, which takes, to insert a new and complex transmission system in anextensive network like the Brazilan, a large amount of work and analysis. Then, for the best alternativeselected, and to assure its technical viability, additional complementary and detailed analysis is carriedon. The selected solution is the reference for a public auction when any qualified transmission agentcan dispute. The new owner can implement either the reference solution, with modification on it, oreven a new alternative. Any choice must fulfil the technical bidden process specification.This paper briefly covers the whole planning process for Madeira Transmission System, since itsconception up to the final design to be implemented.2 ALTERNATIVE SOLUTIONS IN COMPETITIONA previous paper [ 1] presented the feasibility studies for a transmission system to transfer most of thepower generated at Jirau and Santo Antônio hydroelectric plants (6,450 MW), located at the MadeiraRiver in the Amazon region (Porto Velho 500 kV new substation), to the main load center distant2,375 km in Brazil southeastern (Araraquara 500 substation), São Paulo state, as illustrated by Figure1.PORTOVELHOARARAQUARAFigure 1 - Madeira Transmission System location1

2CE3CEThe development and the results of these analyses were carried out considering steady-state operationanalyses, dynamic performance, and economic evaluation. Several alternatives were investigated,including a number of circuit topologies, voltage levels, and different technologies such as DCtransmission, AC transmission and combinations of both. The final conclusion of those studiesrecommended the best solution concerning technical and economic performance, which was atransmission system with two HVDC + 600 kV bipoles (3,150 MW each) and two back-to-backdevices (400 MW each) for connection with a 230 kV system to feed local loads, as illustrated inFigure 2. Besides the long distance point-to-point connection, new reinforcements were planned tointegrate the Porto Velho local load with the main Brazilian transmission system.LOCAL230 kV500 kV+ 600 kV DCPORTOVELHOSTANTÔNIOback-to-backsBT2BT2 3CS-CUIABAR. ARAGUAIAOARARAQUARASoutheastNetworkbipolesJIRAUFigure 2 - DC Alternative solution for Madeira Transmission SystemAt this stage of the transmission planning process, for the first time in Brazil, considering the largeamount of investment involved in such huge transmission system and to encourage competition, theBrazilian authority recommended that at least three different technical alternatives should be takeninto account for the bidding process of Madeira Transmission System. Then, after a large amount ofadditional studies, including all reinforcement necessary to connect the new transmission system in theInterconnected National System (SIN), three alternatives were recommended [ 2], briefly described as:DC Alternative, firstly recommended; Hybrid Alternative (Figure 3), with one DC bipole (3150 MW,+ 600 kV) and two AC 500 kV parallel compensated lines (series and shunt); AC Alternative (Figure4), with three AC 765 kV parallel compensated lines (series and shunt).LOCAL230 kV500 kV+ 600 kV DCSTANTÔNIOPORTO VELHOJIPARANAC. OESTECUIABAR. ARAGUAIASoutheastNetworkARARAQUARAJIRAUA.VERMELHAFigure 3 - Hybrid Alternative for Madeira Transmission System2

230 kV500 kV765 kVLOCALSTANTÔNIOPORTO VELHOJIPARANAC. OESTE3SCCUIABAJAURUR.ARAGUAIASoutheastNetworkARARAQUARA1SCJIRAU3SCA.VERMELHAFigure 4 - AC Alternative for Madeira Transmission SystemThe following stage of analysis, as for any other national grid new transmission system planned inBrazil, requires the recommended feasible solution to be submitted to complementary and detailedevaluation, as described in the next item of this article. It must fulfil all technical requirements, inorder to be eligible for the competitive bidding process.3 COMPLEMENTARY AND DETAILED ANALYSISThis analysis included transients switching simulation, as energization, reclosing, load rejection andshort circuit, using EMTP-ATP (Alternative Transients Program) and EMTDC programs. Foralternatives with DC bipole, power recovery after short circuits, bipole blocking and overvoltages inDC side after faults on DC line were also carried out [ 3]. One of the main concerns of the studies wasto simulate the accelerating torque submitted to the Madeira low inertia bulb type turbo generators(first ever used 83 MW hydro generator), due to fault applications at the AC transmission systemconnected to itThe network represented corresponded to 2012/2013 years, first stage of the Madeira TransmissionSystem, with a small number of generators, and 2017 year, final stage, with all generators at Jirau(46units) and Santo Antônio(44 units) hydro plants. The study was conducted with planning criteriausually adopted in Brazil, similar to those considered for the Itaipu Transmission System [ 4].DC AlternativeOperation points of the AC, HVDC and back-to-back system corresponded to the main configurationsanalyzed in the previous planning process with emphasis to the complete scenario of 2017, whichincludes the two bipoles transmitting its nominal power of 3150 MW, each.The pick value of accelerating torque resulted in 2.5 p.u. at Jirau generators, with generator nominalpower as a base, for a three-phase short circuit at the converter 500 kV AC bus in Porto Velho, asillustrated in Figure 5. For all other conditions simulated, with single or three-phase short-circuits atthe converters AC 500 kV terminals in Porto Velho or Araraquara, maximum values for acceleratingtorque were ranged between 0.7 and 2.0 p.u.3

2.0Santo Antônio3Jirau1.521.010.500.0-1-0.50.0 0.2 0.4 0.6 0.8 1.0(file 2CC600_3F_PV500_dx16_Estat.adf; x-var Domain) SA_Pacc:1-20.0 0.2 0.4 0.6 0.8 1.0(file 2CC600_3F_PV500_dx16_Estat.adf; x-var Domain) JIRAU_Pacc:1Figure 5 - Accelerating torque at Santo Antônio and Jirau after a three-phase fault at S. Antônio500 kV - DC AlternativeThe DC power recovery is limited by the AC system capacity to supply the reactive powerconsumption during the DC power transient. Figure 6 illustrates the DC power recovery at the HVDCPorto Velho rectifier after a 100 ms single phase short-circuit at Araraquara 500 kV AC bus converter.8000Potência CC (MW)8000Potência Reativa (consumo-filtros) (Mvar)5400540028002800200200-2400-2400-5000-50000.0 0.4 0.8 1.2 1.6 2.0 0.0 0.4 0.8 1.2 1.6 2.0(file 2CC600_1F_Ara_dx16_Estat.adf; x-var Domain) Pdc_elo:1(file 2CC600_1F_Ara_dx16_Estat.adf; x-var Domain) Qdc_elo:1Figure 6 - DC power recovery and reactive power at Porto Velho rectifier after a 100 ms shortcircuitin the 500 kV AC bus inverter.The DC power recovery was quite fast for short-circuits with impedance. Last than 150 ms wasnecessary for the DC power recovery to 90% of its initial value. Nevertheless, for three-phase shortcircuitwithout impedance applied to AC 500 kV bus of inverter, this time increased to 350 ms. Forthese cases was recommended that transmission agent, during project implementation, shall adjust thecontrols in order to reduce recovery time. The Porto Velho back-to-back converter has a similarperformance and the same recommendation applied.For transient switching overvoltage DC Alternative had a good performance. For all disturbancesimulated overvoltage pick values situated under expected values, as resumed at Table 1.Table 1 - Maximum overvoltages at different points of network - DC AlternativeSystem represented Disturbance Maximum overvoltage (p.u.)Last stage, AC and DC 2 bipoles and back-to-back 1.2 to 1.45 at 500 kV networkcompleteblockedAC and back-to-back, without Back-to-back blocked1.15 to 1.45 at 230 kVHVDC bipolesLast stage, AC and DCcompleteShort-circuit applied at differentpoints of DC line1.91 at middle of DC line4

Hybrid AlternativeSince the two parallel 500 kV lines were planned to start operation two years in advance of the HVDClink, switching manoeuvres at the AC network were simulated within all segments of the 2,375 kmtransmission corridor, from Santo Antônio to Araraquara. The results showed overvoltage (2.05 p.u.phase to ground) under the admitted criterion limits and ZnO arrester energy limits not violated. Forload rejection, opening of the two lines simultaneously, overvoltages were found in the range of 2.2(without fault) to 2.8 p.u. (with fault) and a recommendation for multiple arresters columns were done.In the last stage of the Hybrid Alternative, with HVDC included, all manoeuvres and load rejections inthe AC 500 network were less severe.Accelerating torque imposed to generators resulted with pick value equal to 3.0 p.u. at Santo Antôniogenerators (generator nominal power as a base), for a three-phase short circuit at Porto Velhoconverter 500 kV AC bus. At this point of final technical analysis, as accelerating torque was apermanent concern, the support of an expert consultant was requested. De Mello[ 5] analyzed theresults of Alternatives DC and Hybrid, and had the opinion that the severity of fault torques is notunusual relative to that found in the industry.The remaining analysis with the HVDC resulted very similar to the DC Alternative, as the bipoles areidentical. This included active power recovery following short-circuits in the AC network, overvoltageat the AC network, and overvoltages at the DC lines due to short-circuit in different points of the line.Even though, there was not doubt about the feasibility of the solution appointed, the analysisrecommended for the future transmission agent to exploit reclosure operations.AC AlternativeEnergization and reclosure of the 765 kV transmission lines were simulated for the first stage ofimplementation with one single circuit from Santo Antônio to Araraquara. The results wereovervoltages (1.9 to 2.14 p.u.) and arrester energy under acceptable limits.For load rejection, final stage with all generators and the simultaneously openness of the threeparallels 765 kV lines were considered, similar to the Itaipu project in the 70s [ 4]. Table 2summarizes the main results.Table 2 - Bus overvoltage and arrester energy due to load rejection - 765 kV AC AlternativeCase Line rejectedSubsequently Max transient Temporarily MaxTerminalsingle-phase overvoltage (p.u.) overvoltage arresterrejectedshort-circuit at Fase to Fase to (at the end of energyground fase simulation) (MJ)1 Porto Velho- Porto Velho ---- 1.79 1.94 1.25 42 Ji ParanáP. Velho 1.93 2.14 - 387 ( 1 ) A. Vermelha----- 1.80 2.02 1.75 ∞7a ( 1,2 ) AraraquaraAraraquara---- 1.80 2.02 1.75 288 ( 1,2 ) Araraquara 1.93 2.16 - 579 Rio Araguaia- Água ---- 1.82 2.01 1.60 ∞9a ( 2 ) A.Vermelha Vermelha ---- 1.82 2.01 1.60 910 ( 2 ) A. Vermelha 1.93 2.35 - 4011 ( 3 ) Rio Araguaia- Água ---- 1.84 2.23 1.77 ∞11a ( 2,3 ) A. Vermelha Vermelha ---- 1.84 2.23 1.77 4412 ( 2,3 ) A. Vermelha 1.93 2.34 - 77Notes ( 1 ) - With openness of 765/500 kV transformer in SE Água Vermelha at the same time of rejection.( 2 ) - With openness of the three 765 kV lines in SE Cuiabá, 300 ms after rejection.( 3 ) - With openness of 765/500 kV transformer in SE Cuiabá.The adequacy of such criterion was reinforced by two recent triple rejections of the Itaipu 765 kVtransmission system. The last one, in November/2009, provoked one of the biggest black-out in the5

Brazilian interconnected power system, nevertheless with no equipments damages as previouslydesigned. The openness of 765/500 kV transformers connected at two substation along the 765 kVroute (Água Vermelha or Cuiabá) were imposed by the overcurrents at these transformers during loadrejection.Temporarily overvoltage resulted high, and consequently with high level of energy at arrester,imposing a prohibitive number of arrester columns (near 10, considering 7.96 MJ per column), evenwhen the openness of the lines at the opposite terminal of rejection was an operation strategy. If suchmanoeuvre is not considered energy results extremely high anyway (cases 7, 9 and 11).The analysis recommended a necessity to re-design the AC Alternative, once typical solutions tomitigate the identified problems were not applied. Planning should point out to feasible solutions withsmall risks for implementation. The AC Alternative was, then, discarded.4 TRANSMISSION SYSTEM AUCTIONDC and Hybrid alternatives competed in an auction promoted by ANEEL (Brazilian regulatoryagency) in November 2008, resulting with the DC Alternative as the winner with annual revenuessmaller (7.15% average) than the established ceiling. The Brazilian regulatory model considers aceiling annual payment for each new transmission element put in auction.In order to improve competition, ANEEL split the transmission system in parts to be offered in thatauction, as illustrated in Figure 7, for the DC Alternative, with seven different lots, including thenecessary reinforcements to accommodate the main transmission system in the national network.The bidding process resulted with different owners for pair of converters (rectifier and inverter) andDC lines. Also each one of the pair of converters was granted to different manufacturers. Theintegration of these two DC bipoles, two back-to-backs and a master control has become a challengesince then.SE Porto VelhoFiltro AC+600kV CC4x2312MCM – 2375kmSE AraraquaraLOT 11575 MVAPólo 11575MWLOT 2 LOT 41575 MVAPólo 21575MWPólo 11475MWLOT 2Pólo 21475MWAraraquara(Furnas)Filtro AC-600kV CC4x2312MCM – 2375km+600kV CC44x71,6MW Filtro AC4x2312MCM – 2375kmAtibaiaS. Antônio4x954MCM - TC - 105kmPólo 1Pólo 11575MW1475MW1575 MVA3x1250MVA1575 MVAPólo 2Pólo 21475MW1575MWFiltro AC4x2312MCM – 2375km-600kV CCLOT 3 LOT 3Jirau44x75MWCuiabá RibeirãozinhoJauru Rio Verde364 km3x(- 70/100) Mvar242kmSI1x750MVA1x750MVABack-to-back1x136 MvarP. Velho Samuel Ariq. J. Paraná P.Bueno VilhenaCoxipo400 MVA400 MVA 2x954MC M12 km 41km 150km 165km 118km 160km 354CECERio BrancoAbuna Univers.- 25/50 Mvar -25/50 MvarLOT 5LOT 7MT-120/250 MvarTrindadeItumbiaraSELOT 6Araraquara(CTEEP)305km 160km 30kmFigure 7 - DC Alternative lots offered in auction6

5 FINAL DESIGN TO BE IMPLEMENTEDThe planning final stage activity requires a demonstration from the new owners that the proposedtransmission system fulfills all technical requirements established before. In a complex transmissionsystem like the one proposed to Madeira a potential number of details have to be discussed withmanufacturers and the new owners, in order to guarantee that the final design conceived by theplanners is ready to be implemented without any constraints.According with the bidding process rules, however, auction entrepreneur winner has the freedom ofdesign optimization of the whole new transmission system, provided that its performance ismaintained equal to or better than the originally planned conceived. As a result, the final solutionproposed to be implemented by the new owners of Madeira Transmission System has some changes,such as:Operation schedule anticipation to match with generation hydro plants schedule.CCC type back-to-back converters instead of conventional type for local load, with no need ofsynchronous compensation in Porto Velho.DC transmission lines bipoles provided with All Aluminum cables instead of ACSR type.DC transmission lines divided in three sections, with distinct project, in accordance with localenvironment, as the long lines cross distinct region of the country.Change in converter filters lay-out reinforcing islanding conception.One of the converter stations provided with three-winding transformers instead of twowinding.Minor changes, like the smooth reactor split with main part installed at lower level voltage.6 CONCLUSIONThe planning process of the Madeira Transmission System within such amount of power to betransmitted, and the long distance crossing different regions of Brazil, was effectively a challenge. Inaddition, selection of three transmission alternative, instead of the tradition one, largely increased theamount of analysis.Even though, the feasibility studies indicated DC Alternative as the most efficient solution, thecomplementary and detailed analysis reinforced this indication and cleared recommended a necessityto re-design the AC Alternative, which was discarded.A new transmission system put in competition, with the actual rules, can contribute to reducetransmission costs, as indicated by the bidding results, with annual revenues for the new transmissionowners averaging 7.15% less than the established ceiling. And even considering a reference solutionselected by the planners, the new transmission owner had the possibility to optimize this solution and,consequently, improve its efficiency.The Madeira Transmission System final design reflects a criterion and efficient process of planning,when the best technical and economical alternative was selected by the planners and its choicereinforced by transmission agents and their financial supporters.7 ACKNOWLEDGEMENTThe authors acknowledge the participation and contributions of the Working Group memberscompounded by the main transmission companies in Brazil (Eletrobras, Furnas, Chesf, Eletrosul,Eletronorte, Cepel, Cemig, Cteep, ONS).7

8 BIBLIOGRAPHY[ 1] Esmeraldo, Paulo C. V. et all. Feasibility Studies for Madeira Transmission System - Technicaland Economics Analysis, CIGRE Session 2008, paper B4-103.[ 2] Integrated system analysis for the Madeira river hydroelectric plants and reinforcements in theInterconnected National System - Reports R1 - Detailing alternatives. Report n. EPE-DEE-RE055r1, May/2008 - in Portuguese.[ 3] Carvalho Jr., Dourival S.; Esmeraldo, P.C V.; Working Group of Reports R2; MadeiraTransmission System - Switching Manoeuvres Evaluation, Cigrê XX SNPTEE, Recife, Brazil,2009 - in Portuguese.[ 4] Peixoto, C.A. et all. Sistema de Transmissão de Itaipu CA/CC - Sobretensões Dinâmicas eTransitórias e suas Influências nas Características dos Equipamentos, VI Seminário Nacional deProdução e Transmissão de Energia Elétrica, Camboriu, SC, Brasil, 1981.[ 5 ] Mello, F.P.; Considerations on the Capability of the AHE Madeira Bulb Type Turbo-Generatorsof Withstanding Accelerating Torque Transients, Consulting Engineer Report, June 2008.8