The Inga-Kolwezi link (formerly Inga-Shaba link) is a 1,700km long, 500kV high voltage direct current (HVDC) power transmission system located in the Democratic Republic of Congo. It is one of the longest HVDC links in the world connecting the Inga hydroelectric complex to the copper mining district of Katanga.

The transmission line is owned by DRC's electricity utility, Societe nationale d'electricite (SNEL). The contract for the construction of the converter stations for the transmission line was signed in 1973.

The HVDC link faced delays due to civil unrest in the country. It was put into operation in 1982 with a transmission capacity of 520MW, which was later upgraded to 1GW in 2017.

Inga-Kolwezi HDVC link details

The 1,700km HDVC overhead lines of the Inga-Kolwezi HDVC link are designed as two separate lines with conductors supported by dual self-supporting lattice steel poles. A space of 40m is maintained between the two transmission lines, which are shielded by a 520mm2 Aluminium conductor steel-reinforced (ACSR) cable.

The transmission line features two transformer terminals to convert the incoming alternating current (AC) to direct current (DC).  The first terminal is located in Inga and the second one in Kolwezi. Both the terminals use six single phase converter transformers and two AC harmonic filters each.

The Inga transformer has a load capacity of 7MVA, while the Kolwezi transformer has 51MVA. Both transformers are connected to a 220kV AC bus bar. The Kolwezi transformer also has three 70MVA synchronous condensers connected to the bus bar.

The transmission line uses double design air cooled thyristor valves, which are fully insulated to the ground. A combination of six double valves forms a 12 pulse converter unit. Each of the valve arms has 43 active modules, with six series connected thyristors giving a total of 258 thyristors in series connection per valve arm.

The electrode station at Inga is located at a distance of 39km from the converter station featuring a linear ground electrode. The Kolwezi electrode station lies 1km away from its converter and is designed as a three-legged ground star electrode.

Inga-Kolwezi HDVC link upgrade

A contract to refurbish and upgrade key technology of the transmission line was issued by SNEL in 2009. The refurbishment and upgrade works included the installation of new thyristor valves and valve cooling systems. The line’s synchronous condensers were refurbished to extend their life and a new Modular Advanced Control (MACH) control and protection system was installed. The upgrade also enabled excess power to be exported to the Southern African Power Pool countries.

The MACH for HVDC control provides fully computerised, advanced fault registration and remote control functions. It consists of station control and monitoring servers, operator workstations, control and protection main computers, digital signal processor units, I/O systems and valve control units.

Another refurbishment and upgrade work was done in 2017 to boost the transmission capacity, enhance grid reliability and extend the lifespan of the line. The work involved installation of new thyristor valves and high-voltage apparatuses, and increasing transmission capacity from 520MW to 1GW.

Contractors involved

ABB, an automation company, was contracted for the design and installation of converter stations in 1973. It also won the contract for upgrade and refurbishment works done in 2009 and 2017.

PSC, a utilities consultant, provided ABB with on-site management of all activities associated with commissioning of the new equipment installed as part of the refurbishment in 2016.

AUTINTEC, an engineering company, was contracted in 2016 for the upgrade works on the Inga-Kolwezi HDVC link.