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Network Interconnection: A Latin connection

Siàƒ¢n Green

In April 1997, the governments of Argentina and Brazil signed an agreement to facilitate cross-border energy trading between the two countries. Just three years on, a 1000 MW power link between the two countries has been completed, and work on a second link is already underway.

The two interconnections will allow Brazil and Argentina to exchange up to 2000 MW of power, helping them to manage their power systems more efficiently. They will be able to take advantage of peaks and troughs in supply and demand, and share their surplus capacity.

The first 1000 MW link between the 500 kV networks of Brazil and Argentina entered operation in June 2000 and is one of the first privately owned independent transmission projects in the world. It consists of a 500 kV transmission line, nearly 500 km in length, running from the Rincàƒ³n de Santa Maria substation near Yacyretàƒ¡ in Argentina, to the Itàƒ¡ substation in Brazil. Because the Argentinean system operates at 50 Hz and Brazil’s operates at 60 Hz, a frequency converter station was built at Garabi in Brazil, close to the border with Argentina. The second 1000 MW link, currently under construction, is almost identical.

The integration of its electricity system with neighbouring countries is an important objective for Brazil, which is struggling to meet rapidly growing electricity demand. The country linked its internal north and south transmission grids in 1999, and has been adding new capacity to the grid. However, electricity demand growth has exceeded GDP growth in recent years, and there is concern that the construction of new generation facilities will not keep pace with demand, resulting in power shortages. A heavy reliance on hydropower has left the country’s power system vulnerable to drought.

In contrast, Argentina’s electricity generating system relies mostly on thermal capacity, including nuclear and natural gas-fired power plants. The two countries will therefore be able to rationalize and balance their deregulated electricity systems through the 2000 MW link, with Brazil securing a reliable source of baseload capacity and Argentina gaining substantial export earnings. In addition, the link will have several other advantages for Brazil; most importantly, it will mitigate supply constraints and help to reduce electricity prices, and contribute to the development of the country’s spot market.

An international tender

Shortly after the signing of the cross-border energy trading agreement by Brazil and Argentina in April 1997, Brazilian utilities Eletrosul and Furnas invited international tenders to develop the first 1000 MW link. In May 1998, the Brazilian Ministry of Mines and Energy, through Eletrobràƒ¡s, and the Argentinean government, signed a 20 year agreement with Companhàƒ­a de Interconexàƒ£o Energàƒ©tica (CIEN), owned by Endesa Group of Spain, for the import of 1000 MW from Argentina’s wholesale market. Furnas and Gerasul will be the main off-takers of the link’s capacity.

In the same month, CIEN placed an order with ABB for the turnkey supply of the complete transmission system, an HVDC converter station, engineering and construction for the 1000 MW link. In addition, a three-year operation and maintenance contract was awarded to ABB.

At the same time, CIEN applied for export and import licences for the second 1000 MW link, which is scheduled to enter commercial operation by 1 May 2002. This second phase is based on negotiated power sale agreements (PSAs) between CIEN and Companhia Paranaese de Energia (Copel), the electricity distribution company for Brazil’s Parana state.

Figure 1. The first 1000 MW link entered operation in June 2000
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On completion of the second 1000 MW link, CIEN will enter two PSAs with Copel for the offtake of a total of 800 MW. The remaining 200 MW of capacity will be sold to a number of additional offtakers. To meet these obligations, CIEN will also enter a 1000 MW power purchase agreement (PPA) with Argentina’s Comercializadora de Energàƒ­a del Mercosur (Cemsa), a company controlled by CIEN, which will take commitments from Argentinean generators.

Copel will therefore buy the majority of the available capacity of the second 1000 MW link. Copel is perceived as one of the strongest and best managed energy companies in Brazil, with a market capitalization of $2 billion in December 1999 and a net income of $73 million in 1999. It is active in all areas of the electricity business, and in addition to providing service to the state of Parana, also sells electricity to other Brazilian states.

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Financing for the projects has come from a variety of sources, including the Brazilian Development Bank (BNDES), the Inter-American Development Bank, and the Spanish bank Santander.

Challenging prospects

The time scale for the completion of the first interconnection was tight: just 22 months from the signing of the contract with CIEN to commercial operation. This was one of the biggest challenges for ABB, and required considerable innovation in both manufacturing and construction techniques for the transmission lines and converter station.

In order to meet the schedule, the engineering and construction of the transmission line, the environmental impact studies and right of way acquisition had to be completed within 19 months. Environmental considerations were of particular importance as the transmission lines pass through various historically important regions as well as nature reserves. Close cooperation with local, state and federal authorities was required, as well as with archaeologists.

The length of the transmission line from the Rincàƒ³n de Santa Maria substation in Argentina to the converter station at Garabi in Brazil is 136 km, and includes a special crossing over the River Uruguay. This 50 Hz, single circuit line has a nominal voltage of 500 kV. The suspension towers are flat configured guyed-V and the dead-end towers are self-supporting, all in galvanized steel.

Figure 2. The 2000 MW link will allow Argentina and Brazil to manage their power systems more efficiently
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At the border between the two countries, a special river crossing was required. Here, the length of the transmission line is 2 km, with a maximum span of 856 m and raised suspension towers with a height of 90 m.

The transmission line in Brazil, from Garabi to Itàƒ¡, is 356 km long, and has a nominal voltage of 525 kV and a frequency of 60 Hz. The suspension towers are similar to those used in Argentina.

The two electrical systems are both large, but have been interconnected at relatively weak points in their networks. The Rincàƒ³n de Santa Maria substation is at the northeastern extreme of the Argentinean system, and although it adjoins the Yacyretàƒ¡ hydropower plant, it can have a relatively low short circuit capacity, depending on how many generators are connected at Yacyretàƒ¡.

Similarly, the Itàƒ¡ substation is in a remote location on the southern extension of the Brazilian south-southeast interconnected system. While a relatively short transmission line length of 136 km exists on the Argentinean side of Garabi, the line length of 354 km to Itàƒ¡ presented a challenge for the operator of a converter station who has to guarantee delivery of 1000 MW at a weak point in the system.

To help reinforce the power supply to Brazil, the transmission line on the 60 Hz side was sectionalized at Santo Angelàƒ´. However, this step will not be necessary for the second interconnection project. In addition, to overcome the challenges presented by low short circuit levels, especially on the 60 Hz side, capacitor commutated converters (CCCs) are used at the converter station, allowing the converter to absorb or supply reactive power as required.

Modular designs

Figure 3. The phase one converter station consists of two 550 MW blocks
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The converter station at Garabi performs the frequency conversion from the 50 Hz, 500 kV Argentinean AC network to the 60 Hz, 525 kV Brazilian AC network, and is also key in fulfilling the electrical performance requirements of the system. The converter station consists of two converter blocks of 550 MW each, thus ensuring delivery of 1000 MW at Itàƒ¡ even under low voltage conditions.

The harmonic filters are in two banks, each associated with a converter block. Each bank consists of 11th and 13th ConTune band pass branches, and 24th and 36th high pass branches. The ConTune band pass branches for the 11th and 13th harmonics have automatic tunable reactors in series with capacitors, while the high pass branches are of conventional design. The inductance of the tunable branches are adjusted continuously to compensate for temperature and frequency deviations.

A rather novel bus arrangement has been used to ensure that the availability figures – energy availability of over 97 per cent – are met. The converter transformers are of the single phase three winding type. Each 12-pulse converter block has six transformers, or the same design on both the 50 Hz and 60 Hz sides, thus requiring only one single phase spare unit.

The converter valves are in modular housings, factory assembled and tested, and were shipped to the site ready for operation. The control equipment and auxiliaries were also factory assembled and tested to reduce the installation and commissioning time.

All the converter bus breakers are of a modular compact design, with breaker, disconnects and optical current transformer integrated into one unit. The compact breaker can be quickly installed and removed, allowing efficient maintenance and facilitating the expansion of the converter station during the second 1000 MW interconnection project.

The controls, protections, event logging and fault recording are integrated into a PC-based control system – ABB’s Mach 2. This is a totally redundant system with a high degree of functional integration and an open systems interface approach. The control of the transmission system can be performed locally on a per-block basis, or the two blocks can be run as one unit from the local station control building or from remote locations in Argentina and Brazil.

In the CCC system, commutation capacitors are placed between the converter transformer and the valves, providing the capacity for reactive control, as well as ensuring stable operation of the converters at low short circuit levels. The converter therefore acts like a static compensator, giving smooth continuous control of voltage and power flow.

The modular design of the HVDC converter station meant that a short construction time was possible for the first phase, and also that an area of only 138 000 m2 was required for the complete 1100 MW converter station.

Active connection

In June 2000, the first 1000 MW link successfully entered commercial operation. Because of the recent shortage of power supplies in Brazil, the link is, according to ABB, operating almost continually at full capacity. A power transfer was also made to Argentina for a short period due to transmission constraints in the south system.

ABB announced in June 2000 that CIEN had awarded it the $250 million contract to construct the second 1000 MW link between Argentina and Brazil on a turnkey basis. This second link will be virtually a copy of the first from a technical point of view, comprising 490 km of AC transmission lines running from the Rincàƒ³n de Santa Maria substation in Argentina to Itàƒ¡ in Brazil, and an HVDC converter station at Garabi. As part of this second order, ABB will expand the substations associated with the first link, and will integrate the two projects.

Compatible systems: Brazil and Argentina
Brazil: Brazil has an installed electric capacity of 62.4 GW, approximately 85 per cent of which is hydropower. Of the 316.9 TWh generated in Brazil in 1998, 91 per cent was from hydropower resources. Brazil’s remaining electricity generation capacity comes from coal and an ever-increasing amount from natural gas. Electricity demand is growing rapidly, however, and the country is taking several measures to improve its power supply system, including privatization and the introduction of competition in generation.

Brazil’s northern and southern electrical grids were joined in January 1999 into one grid that serves 98 per cent of the country. As well as importing power from Argentina to help meet demand, plans to import electricity from Venezuela moved ahead in April 2000, when Venezuela announced that it had reached agreements with indigenous peoples living along the border area allowing construction of 500 km of electric transmission lines to join the two countries.

Argentina: Argentina relies mostly on hydropower and natural gas to fuel its electricity sector. In 1998, the country had 21.8 GW of installed generation capacity, of which about 53 per cent was fossil fuel-based (primarily natural gas), 42 per cent hydroelectric, and about five per cent nuclear.

Argentina has one of the most competitive deregulated power sectors in South America. Since 1991, the government has pursued an aggressive privatization programme in tandem with the creation of an open electricity market, which has attracted foreign investors and project partners. Today, power generation capacity generally satisfies domestic demand.

Brazil and Chile are the two most important export markets for Argentina, and the three governments are integrating their electricity markets and moving towards free competition among generators, a ban on state subsidies, and a cost-based pricing system. A 2000 MW interconnection with Uruguay’s electric system has been in effect since 1974, and Uruguay often exports electricity to its western neighbour. Several trans-Andean power line projects offer the prospect of increased electricity sales to Chile.