ABB plans to build two 1200 MW transmission systems in north and northeast Brazil which will reinforce the existing system, bringing reliability and stability to the grid.
The unrelenting demand for electrical power in Brazil has accelerated the need for new transmission systems that can be built within very short lead-times in order to transport large blocks of power across a continental area of approximately 8.5 million km2.
Among the newest projects in development are two 500 kV transmission systems in north and northeast Brazil, each with a capacity of 1200 MW and a combined length of nearly 1300 km. Both interconnections will reinforce an existing 500 kV system that ties into the heart of the northern Brazilian power grid, the Hydro Power Station of Tucuruí, which itself is currently being expanded. The two new interconnections will strengthen the reliability and stability of the existing grid as well as the efficiency of exchange between regional power generation plants.
Agência Nacional de Energia Elétrica (Aneel), the government’s energy regulatory agency which oversees the transmission system, auctioned the contract for the construction of the two new interconnections for the Tucuruí power plant in order to reinforce the country’s basic power grid.
ABB will be expanding four substations and building one new one
A consortium of power developers comprising the construction company Schahin and the electrical contractor Alusa, won the concession and was granted the right to build, own and operate (BOO) the two new power lines in north and northeast Brazil.
Schahin/Alusa then initiated another bidding process, seeking companies offering cost-effective solutions that could be engineered in a matter of months. The consortium awarded ABB the $300 million contract to design, procure and construct the transmission line components and corresponding substations.
This is the first expansion involving the Tucuruí power plant, which is already one of Brazil’s largest plants. The capacity of the 8000 MW station is being expanded by one third, and many more hydropower plants are being planned along its grid, a development that will require the reinforcement of existing transmission lines.
From Tucuruí, large power trunks working at a nominal voltage of 500 kV connect the north and southeast grid, which makes-up the country’s critical North-South transmission backbone.
Another line between Tucuruí and Presidente Dutra ties into the north and northeast grids. A further line connects Tucuruí and Vila do Conde to the north, and is part of the Tucuruí Hydraulic power plant transmission system that belongs to Eletronorte (Eletricas de Norte do Brasil SA), the electric power generation and transmission utility serving the Amazon region.
ABB will be building a new Tucuruí-Presidente Dutra transmission line and a new interconnection between Tucuruí and the Vila do Conde substation, both of which will run parallel to the existing interconnections. The new lines are designed not only to increase the power supply in northern Brazil but also to improve the reliability and stability of the grid’s power transmission, thus helping prevent power outages, disturbances in the system, and the disconnection and reconnection of major generators.
The challenge inherent in this project is to build 1300 km of 500 kV lines in a tropical region, together with five corresponding substation installations and 1500 MVAr series compensation equipment within an accelerated timescale, and in one go.
The Tucuruí-Vila do Conde interconnection is scheduled to be in operation in August 2002, with 325 km of transmission lines crossing eight municipalities in the State of Para.
ABB has designed a simple and robust transmission line system based on guyed cross-rope suspension towers
The 944 km-long Tucuruí-Presidente Dutra line will cross through the states of Para and Maranhao and will require 22 months to complete, with the onset of commercial operations slated for April 2003.
The tight timetable and magnitude of the project has required careful planning that incorporates regulatory, climatic and environmental considerations as well as technical solutions that will provide long-term benefits to consumers.
In order to capitalize on the time and resources available at each given construction site, ABB will divide the transmission lines into several sub-sections and build them parallel to one another. In addition, ABB has designed a simple but robust transmission line system based on guyed cross-rope suspension towers that are easier and quicker to build than conventional structures. They require only small foundations, which will be much easier to build in the face of heavy tropical rains and will also help to minimize the project’s environmental impact.
Environmental issues were given special consideration during the planning process. Under Brazilian law, a project of this kind requires an environmental impact assessment report, a base-line of the existing situation and an environmental plan. The entire application process takes between four and six months and calls for thousands of engineering man-hours.
Schahin/Alusa is responsible for obtaining the licenses, while ABB supports the applications with descriptions of the system and its construction. For example, following a series of topography, soil, access and other surveys, a detailed application must be submitted for each tower type, height and design and for each individual location where the tower is to be built.
Given the importance of this interconnection, the Brazilian government has asked the responsible authorities to give priority to applications related to the project. In addition, in order to avoid potential complications and delays in the approval process, the interconnections will deliberately avoid passing through two important sites. The Tucuruí-Vila do Conde line will circumvent the rapidly growing city of Tailandìa, and the Tucuruí-Presidente Dutra line will bypass the Mother Maria Indian reservation.
A technical cornerstone of the Tucuruí interconnections is the guyed cross-rope tower that ABB has developed. Towers of this type have already been in operation for two years along the Comahue transmission line in Argentina.
These compact, lightweight towers are faster and easier to build than traditional self-supporting structures and can be completed in around half the time with one-third less construction crew. They are also cost-effective and provide the same level of performance and service life as conventional towers.
The new lines will increase power supply in northern Brazil and will also improve the reliability and stability of the grid
About 70 per cent of the 3000 towers to be built for the Tucuruí interconnections will be of the cross-rope type. This is because this type of structure is designed specifically for use in straight line applications and can only accommodate a maximum deviation of two degrees. So in locations where the line has to ‘bend’, for example to go round a lake, traditional, heavier self-supporting Racket and Delta towers will be used.
The cross-rope tower consists of two masts forming a V-shape, connected at the top by ropes. The towers’ foundation consists of a central cap foundation with two 12 m depth micropiles. The conductors configuration is a bundle of four with a spacing of 457 mm between the ACSR Rail 954 MCM conductors.
Series capacitors have been utilized for many years with excellent results in many parts of the world. The stability of the transmission system will be enhanced through the series capacitor banks, which are designed to suppress part of the line’s electrical reactance. This process effectively shortens the electrical parameters of the line, allowing it to carry the 1200 MW at 500 kV over extremely long distances.
The impact of the series capacitors can most easily be explained as a combination of three mechanisms, working in parallel:
- Increased angular stability of the power transmission corridor
- Improved voltage stability of the power corridor
- Optimized power sharing between parallel circuits.
ABB will be expanding four existing substations and building one new one. The Tucuruí substation will feature two line entrances, one to link into the Vila do Conde transmission line, the other into Presidente Dutra.
The Tucurui-Presidente Dutra interconnection will feature five substations – the four existing at Tucuri, Maraba, Imperatriz and Presidente Dutra will be upgraded and a new one will be constructed at Acailandia. In total, they will encompass eight 33.3 MVAR reactors, four 54.3 MVAR reactors, eight 60 MVAR reactors and four 72.5 kV neutral reactors. There will be a total of four 500 kV capacitor banks and fourteen 500 kV circuit breakers, fifty-six 500 kV surge arresters and four 54 kV surge arresters. There will be a total of 47 disconnector switches, 31 without grounding blades, 16 with one. Forty-two 500 kV current transformers will be installed, twenty-six 500 kV voltage transformers and sixteen 500 kV line traps.
Every transmission line between the substations is controlled and protected by microprocessor systems using ABB’s latest generation of digital control technology. Every substation provides access to the entire system; lines can be switched and manoeuvred from a variety of different locations.