Caprivi Link

The Caprivi Link Interconnector is an HVDC (High Voltage Direct Current) transmission project connecting the electricity networks of Namibia and Zambia. This project marks a significant advancement in VSC technology, being the first commercial application for overhead transmission lines and operating at a voltage rating of 350 kV DC.

The Caprivi Link consists of a 970 km ±350 kV HVDC bipolar line with a capacity of 300 MW, upgradeable to 600 MW. It connects the Zambezi converter station near the Zambian border to the Gerus converter station in central Namibia. The project, commissioned on November 12, 2010, cost approximately N$2.9 billion ($360 million) and was funded by various international financial institutions.

Technical Specifications

The HVDC system employs 2-level Voltage Sourced Converter (VSC) technology. It operates as an asymmetrical monopole configuration with a power transmission capacity of 300 MW. The system connects to 330 kV AC at the Zambezi converter station and 400 kV AC at the Gerus converter station.

Converter Stations

Both converter stations are capable of converting power from AC to DC and vice versa. The Zambezi station is located in the Caprivi Strip, while the Gerus station is situated near Otjiwarono in Namibia's Otjozondjupa region. Each station includes AC filters, IGBT valves, converter reactors, converter transformers, DC capacitors, and smoothing reactors.

Transmission Line

The 970 km overhead transmission line operates at ±350 kV DC with a nominal current of 857 A. The project also includes approximately 50 km of electrode lines connected to earth electrodes at both ends.

Operational Capabilities

The Caprivi Link can transmit power bidirectionally, allowing for both import and export of electricity between Namibia and Zambia. It can handle power flows from +300/600 MW import to -280/560 MW export without switching AC filters. The system provides ±200 MVar of continuous AC voltage control for the connected 400 kV/320 kV grids.

Grid Stability Features

The VSC technology enables stable power transfer in weak AC networks with short circuit powers as low as 300 MVA. It can operate in islanded mode, providing frequency control to isolated AC grids. The system can restart after DC line faults due to lightning within 500 ms of fault clearing.

Environmental Considerations

The use of DC transmission reduced the project's environmental footprint compared to an equivalent AC line. The narrow Caprivi Strip's unique geography made HVDC an optimal choice for long-distance power transmission.

Challenges and Innovations

As the first significant transmission line application of VSC technology, the project faced challenges related to disturbances such as lightning strikes and bushfire-induced flashovers. These issues required the development of rapid fault clearance systems, which initially caused some operational delays and damage during testing.

Regional Impact

The Caprivi Link plays an important role in the Southern African Power Pool (SAPP), enhancing energy trading potential and improving the dynamic stability of the regional transmission network. It provides an alternative wheeling path for electricity trades within SAPP and supports the development of new hydropower plants in Zambia.

The Caprivi HVDC project offers improved grid stability, increased power trading capabilities, and support for renewable energy development in Southern Africa.