Cahora Bassa Dam

The Cahora Bassa Dam is a dam in Mozambique. It is one of the three major dams on the Zambezi river system, the others being the Kariba and the Itezhi-Tezhi, the latter on the Kafue River, a tributary of the Zambezi.

History

The dam began to fill in December 1974 after construction was commenced in 1969 by the Portuguese colonial government of Mozambique (Portugal), and is 171 metres (561 ft) high by 303 metres (994 ft) wide at the crest. Built in the first half of the 1970s when Mozambique was still a Portuguese territory, long stretches of the power transmission lines were sabotaged during 16 years of Mozambican Civil War which ended in 1992.

The lake has reached a maximum length and width of approximately 250 kilometres (160 mi) and 38 kilometres (24 mi) respectively, flooding an area of 2,700 square kilometres (1,000 sq mi) with an average depth of 20.9 metres (69 ft).

Power stations

The Cahora Bassa system is the largest hydroelectric scheme in southern Africa with the powerhouse containing five 415 megawatts (557,000 hp) turbines. Most of the power generated is exported to South Africa, which is done by the Cahora Bassa HVDC system, a set of High voltage direct current lines. The system includes two converter stations, one at Songo in Mozambique and the other at Apollo in South Africa. There are two parallel power lines between these two stations, covering 1,400 km, of which 900 km is in Mozambican territory. These HVDC lines work at 533 kV and in Mozambique territory only have about 4,200 towers.

Cahora Bassa

The Cahora Bassa lake—in the Portuguese colonial era (until 1974) known as Cabora Bassa, from Nyungwe Kahoura-Bassa, meaning "finish the job"—is Africa's fourth-largest artificial lake, situated in the Tete Province in Mozambique. In Africa, only Lake Volta in Ghana, Lake Kariba, on the Zambezi upstream of Cahora Bassa, and Egypt's Lake Nasser are bigger in terms of surface water.

History

Portuguese period

The Cahora Bassa System started in the late 1960s as a project of the Portuguese in the Overseas Province of Mozambique. Southern African governments were also involved in an agreement stating that Portugal would build and operate a hydroelectric generating station at Cahora Bassa together with the high-voltage direct current (HVDC) transmission system required to bring electricity to the border of South Africa. South Africa, on the other hand, undertook to build and operate the Apollo converter station and part of the transmission system required to bring the electricity from the South African/Mozambican border to the Apollo converter station near Pretoria. South Africa was then obliged to buy electricity that Portugal was obliged to supply.

Cahora Bassa (HVDC)

Cahora-Bassa (previously spelled Cabora Bassa) is the name for an HVDC power transmission system between the Cahora Bassa Hydroelectric Generation Station at the Cahora Bassa Dam in Mozambique, and Johannesburg, South Africa.

History

The system was built between 1974 and 1979 and can transmit 1920 megawatts at a voltage level of ±533 kilovolts and 1800 Amperes.Thyristor valves are used, which unlike most other HVDC schemes are mounted outdoors and not in a valve hall. The valves are grouped into eight, 133 kV six-pulse bridges in series at each end. The 1,420 kilometres (880 mi) long powerline runs through inaccessible terrain, so it is mostly built as monopolar lines 1 kilometre (0.62 mi) apart. In case of a single line failure, transmission with reduced power is possible via the surviving pole and return through the earth.

Cahora-Bassa was out of service from 1985 to 1997 because of the Mozambican Civil War in the region. The project was beset with technological challenges, most notable of these being the adoption of solid-state rectification devices in a large-scale commercial installation. Mercury-arc valves had been the de facto standard for HVDC up to this time. Cahora Bassa was the first HVDC scheme ordered with thyristor valves, though its operation was delayed. It was also the first HVDC scheme operational in Africa, and the first anywhere in the world to operate above 500 kV. Significant commercial hurdles, culminating in hearings at an International Arbitration Tribunal seated in Lisbon, in 1988, also had to be overcome.