Transmission Grid Development
Thomas Jauch, ABB Power Technologies
On the backs of buffaloes or via wooden bridges built on site, ABB engineers relate how they constructed 1267 km of two power transmission systems for the companies Schahin and Alusa between the north and northeast regions of Brazil.
One of the largest power transmission projects to have been built in Brazil over the last few years was entrusted to the company Empresa Amazonense de Transmissão de Energia (EATE), [Amazon Energy Transmission Company] established by the companies Schahin and Alusa. During a 19 month period, the various teams involved in the project collaborated in constructing a power line of 943 km of extension, with 2032 towers, 14 500 t of metallic structure and four series capacitor installations.
The new system, already in operation, interlinks a region with an enormous hydroelectric potential to generate energy to the system that feeds the remainder of Brazil. The line brings together the substations in existence at the towns of Tucuruí and Marabá, in the state of Pará, and other substations in the towns of Açailândia, Presidente Dutra and Imperatriz, located in the state of Maranhão.
The new system interlinks a region with an enormous hydroelectric potential to the system that feeds the remainder of Brazil
With the completion of this project, the authorities responsible for the Brazilian electrical power system have managed to interlink the north and northeast areas of the country onto the national grid system. This will allow for energy generated in the Amazon region to be used by Brazilians on the frontiers with Argentina and Uruguay. In order to make this dream a reality the consortium needed to invest some R$650 million ($227 million).
The line was put up for bidding at a transmission auction carried out by Aneel in April of 2000. Geir Biledt, director for ABB’s large transmission systems in Brazil, was responsible for coordinating all of the negotiations for the construction of the transmission system between Tucuruí and Presidente Dutra.
ABB was contracted to construct the power transmission system between the two regions in June 2001, and undertook the project for EATE on a turnkey basis. The last stretch of the new line was completed and handed over on March 10, 2003 and is going to reinforce the provision of energy between the north and northeast regions.
Constructing the 943 km transmission line in only 12 months was an enormous undertaking. The field teams were required to work at a blistering pace – averaging 7.73 foundations built, 9.30 towers erected and 6.10 km of cables positioned per day (See Table 2). “What was built and mounted within a year was work for a period of between 24 and 30 months, under normal conditions”, explained Geraldo Vieira, ABB’s manager responsible for the project between Tucuruí and Presidente Dutra.
A CSM-type self supported tower in place at the Tucurui-Vila do Conde power transmission line in Brazil
Maintaining a well-distributed support network was fundamental to the daily feeding of material and supplies to the operations. The supply strategy adopted by Vieira was to install a support field team at every 100 km along the project. Consequently, ABB mounted installations of this type at the towns of Jacundá, Nova Ipixuna and São Pedro da Água Branca, in Pará, and at Santa Luzia, Boriticupu, Lago da Pedra and Joselândia, in Maranhão.
The strategy proved to be an effective one; the aggressive timetable for the completion of the transmission line between Tucuruí and Presidente Dutra was not only met but was shortened.
According to Marcelo Tosto, a director at the company Empresa Amazonense de Transmissâo de Energia (EATE), the date contracted with Aneel for putting the system into operation was April 12 2003.
The first stretch was handed over on January 31 2003, and the final stretch March 10. “The anticipation of the timescale varied between one and four months”, Tosto explained. “The schedule timescale of 21 months for the completion of a 900 km power transmission line is already a benchmark. The performance was very good when taking into consideration the time necessary for obtaining the environmental license.” he added.
The line went into commercial operation shortly after March 10. “There is already power being transmitted through it from the north to the northeast regions, something in the order of 700 MW.” Tosto explained.
The greatest challenge that ABB faced in building the transmission line between Tucuruí and Presidente Dutra was to ensure quality in this fast track project. The use of FACTS (flexible AC transmission systems) on the line was part of the technical solution to provide reliability and stability. The 500 kV power line included four series compensation banks, a FACTS technology used to reduce the transfer reactance of the long power transmission corridor. This is beneficial for power transmission, as it improves voltage control and increases the dynamic stability of the link.
The use of FACTS improves power transmission capability under varying conditions and reduces losses as well. Without the series compensation installations, additional transmission lines would have been necessary in order to transmit an equal amount of energy. In addition to series compensation, shunt reactor compensation was implemented at intervals along the line, in order to maintain satisfactory system conditions over the full range of power transfer.
The scope also covered high-tension equipment, which loomed as another challenge. The most critical moment of the whole process of mounting occurred when the equipment and metallic structures were being delivered. At that point only three months remained for all of the equipment to be mounted, tested and commissioned. Through the partnership among ABB’s teams in Brazil and in Sweden, it was possible to successfully manage to plan and execute an assembling and commissioning programme to overcome the difficulty of doing so much in such a short space of time.
The aggressive timetables for completion of the transmission lines were met, and, in some cases, shortened
The most difficult moment in testing came at the Imperatriz substation, which, even though it had required the least civil construction work of the five, was in fact the most complex. This was due to the numerous integrations that were necessary since it is one of the most important substations within the national electrical grid system, as it connects the grid networks of the south to the north of Brazil.
All of the integration work was preceded by a technical study and could only be executed after the approval of the Operador Nacional do Sistema (ONS) [National Grid Operator]. Everything took place at dawn when the Brazilian electrical grid system is less vulnerable to possible disturbances. Any error or unforeseen happening at the moments of integration of the network grids and equipment would cancel out posterior actions, consequently slowing down the energy coming on the power line.
The 943 km line between Tucuruí and Presidente Dutra was built parallel to another system of some 324 km in distance between Tucuruí and Vila do Conde, both with substations in the State of Pará. The town of Tucuruí is the start of these two lines because the hydroelectric power station that bears the same name is being extended. In this extension phase, the hydroelectric power station, built in 1984, will receive a new powerhouse with a further 11 units, each of 350 MW, to be put in place at a rate of one every four months. Added to the 12 generators already in operation, this will raise the generation capacity from around 4100 MW to 8370 MW, when it will then become the largest totally Brazilian hydroelectric power station.
Itaipu, in spite of being larger, is bi-national, belonging to both Brazil and Paraguay. The extra energy will be sufficient to attend to 40 million inhabitants and the lines built by ABB will therefore serve to spread this power load throughout the whole of the national interlinked grid system. When the ABB engineers got the first batch of data concerning the geography of the region between Tucuruí and Vila do Conde, they quickly perceived that the solutions as far as towers could not be the same as those used in ABB’s worldwide civil engineering work. Studies confirmed that the soil had a high content of sand and therefore a much softer composition. In some areas of frequent precipitation, flooding was a daily occurrence. Dense and humid forestland made the transportation of equipment and material difficult. There was the necessity for the implementation of new techniques and to come to terms with the unprecedented demanded timescale of 14 months.
ABB was also contracted to construct the power transmission line between Tucuruí and Vila do Conde in June 2001. It has an extension of some 324 km, with 706 towers, 5515 t of metallic structure and the capacity of 1200 MW. The new line was handed over on August 9 2002 and currently reinforces the provision of electrical energy to the Pará state capital, Belém, previously served only by one transmission circuit.
ABB undertook the project using turnkey methodology for the company Empresa Paraense de Transmissão de Energia (ETEP), a company specially established by the companies Schahin and Alusa to lead the construction of the system, whose concession had also been up for bidding at the transmission auction carried out by Aneel in April 2000.
In order to comply with the timescale of 14 months, a special scheme was mounted that divided up the work into sections constructed in parallel. The engineering for the project, the provision of material and the carrying out of the constructions were done simultaneously. The rhythm of the work was intense, though less so than that employed going to Presidente Dutra. Every day foundations were dug for 4.23 towers, 4.36 towers were mounted and 3.68 km of cable was laid down. This did not impede the carrying out of studies and detailed adaptations, in accordance with the environmental demands of the region. For example, the town of Tailândia, under expansion, was by-passed by the transmission line in order to avoid environmental problems.
Another of the project’s challenges was to adequately place piles given the region’s geography and soil conditions. For example, 11 towers passed over the river Moju. ABB engineers had to install concrete piles in the depths of the river where towers passed – two of them with 98 m in height.
In addition, some 7000 m of sustaining structures were dug throughout the swampy marshlands. Creativity was required in the logistics that were used to carry the parts and tower structures to the work on-site, which flooded during a large part of the year. In one case, while constructing the wooden bridges (known as estivas) used for the transportation of equipment, the engineers placed the parts on the backs of teams of 10 to 15 buffaloes in order to reach the work sites.
The design of the towers was a determining factor in managing to cut time off the project schedule. In addition to using towers of the racket type, towers of the “cross rope” type – unprecedented in Brazil – were used in order to construct the line within the contracted timetable. Another difference in the project was the use of helicoidal piles for the foundation of the tower mainstays, a solution that reduced time, minimized environmental impact, and was better adapted to the wet soil conditions of the region. In this manner the towers were erected in half the normal time, and involved a third of the team that would have been necessary if only the traditional racket type towers had been used.
By opting to use towers of “cross rope” type in the four stretches that make up the line between Tucuruí and Presidente Dutra, instead of maintaining the normal racket type towers, ABB managed to reduce the cost of the project by 20 per cent. This cost reduction included the structure of the towers, the sustention and auxiliary cables as well as the foundations cost. The principal factor in the cost reduction relates to the average weight of the structures per km of transmission line. In a transmission line of 500 kV, typical of the region, using compact suspension structures of “cross rope” type, there are some 15.6 t of structure/km of line. This is 32.2 per cent less than a compact tower system of the racket type, where there are 23 t of structure per km of line
Throughout the project, some 7000 m of sustaining structures were dug throughout the swampy marshlands
Transporting energy has turned itself into a business niche for the companies Schahin and Alusa. The two companies, originally from the civil construction sector, have transformed themselves into large investors within this market. At the last concession auction for the construction of new power lines, sponsored by Aneel on August 15, the consortium that brings the two companies together won bids for two more sections. The first interlinks the towns of Tucuruí, in Pará, and Açailândia, in Maranhão. The second unites the municipalities in the state of Pará of Vila do Conde and Santa Maria. The forecast is that the two new business enterprises will receive in total investments in the order of R$475 million ($167 million). Adding this on to the concluded project (Tucuruí – Vila do Conde) and to those being carried out (Tucuruí – Presidente Dutra and Campos Novos Blumenau), the Schahin/Alusa consortium is dealing with a total of 2140 km of concessions. It is an outstanding contribution towards the development of the Brazilian electrical energy system.