The Cahora Bassa HVDC transmission provides an important power import facility to the South African grid. It transmits 1920 MW of power from the Cahora Bassa generating station on the Zambezi River in northern Mozambique. The original transmission was put into service in three stages from 1977 to 1979.
The system includes two converter stations, one at Songo in Mozambique and the other at Apollo in South Africa. They were built by the ZAMCO consortium (AEG; BBC and Siemens). The transmission, which is owned by Hidroeléctrica De Cahora Bassa in Mozambique and Eskom in South Africa, comprises two parallel monopolar lines, covering 1,400 km, of which 900 km is in Mozambican territory.
The Apollo converter station refurbishment
In 2006, the South African power company, Eskom, awarded a contract to ABB for the refurbishment of the Apollo converter station. The upgraded Apollo substation, boosts transmission capacity of the substation from 1,920 MW to 2,500 MW. It also prepares for a future upgrade to 3,960 MW. The upgrade significantly increases the availability and reliability and reduces the maintenance of the Apollo station.
The new outdoor valve assembly
at the Apollo station.
|.||ABB’s unique air-insulated outdoor thyristor valves that replaced the old oil-insulated valves are mounted on the existing support insulators for the old valves. Thereby significant savings were made, since minimum changes needed to be made to the physical arrangement.|
The upgrade was perfomed in shortest possible time, and with minimum disruption of the power transmission capacity of the link. The transmission capacity was reduced by 50 % during a period of three months, and by 25 % during two months.
The Songo converter station refurbishment
In 2012, Hidroeléctrica De Cahora Bassa in Mozambique awarded ABB the contract to replace key high-voltage equipment, i.e. transformers, DC smoothing reactors, arresters and measuring equipment in the northern station, Songo. The refurbishment enhances power availability and improves system reliability.
The commissioning will be completed in two parts, the DC equipment in 2013 and the transformers a year later.
|Commissioning year: ||1977 - 79|
|Apollo refurbishment: 2008|
|Songo refurbishment: 2013-2014|
|Power rating: ||1 920 MW|
|No. of poles:||2|
|AC voltage:||220 kV (Songo), 275 kV (Apollo)|
|DC voltage:||±533 kV|
|Length of overhead DC line:||1 420 km|
|Main reason for choosing HVDC:||Long distance|
|Application:||Connecting remote generation|