HCB (Hidroeléctrica de Cahora Bassa), which owns and operates the Cahora Bassa hydroelectric power station on the Zambezi River near Songo in Mozambique, contracted WSP in Africa’s transmission and distribution team to provide expertise to the process of rehabilitating and replacing equipment at the Songo HVDC converter station in order to improve its reliability, availability and maintainability (RAM).
Mozambique has the largest power generation potential of all Southern African countries and is capable of generating as much as 187 gigawatts of power from its coal, hydro, gas, solar and wind resources. The Cahora Bassa system, commissioned between 1974 and 1979, is one of the most important power transmission systems in the region.
The majority of Cahora Bassa’s power is transmitted to South Africa, where it contributes more than 1000 MW to the South African grid. The Songo HVDC converter station is critical to this supply, exporting power from the power station to the Apollo inverter station in South Africa. The scheme is capable of dispatching up to 1,920 MW through the 1,414 km high voltage direct current (HVDC) 533 kV transmission lines between these two converter stations.
“Ageing and unreliable equipment, resulting in poor performance of the Songo station, was the biggest challenge our client needed to address,” said Dinesh Buldoo, Director: Power - Transmission and Distribution, WSP in Africa.
Buldoo indicated that working in a live yard meant outages had to be minimised during all the project phases undertaken. “Other challenges experienced on this project included the failure of the Pole 1 DC smoothing reactor during the procurement phase, which emphasised the urgency of replacing this equipment, and these pressures were further compounded by needing to negotiate with the contractor to expedite the replacement air-core DC smoothing reactor for Pole 1. And, unexpected ground conditions and rehabilitation works of the old converter transformers also contributed to making this a challenging project."