This scheme, equipped from the outset with thyristor valves provided by Swedish subcontractor ASEA, was designed to transmit 560 megawatts, in the first phase, at a symmetrical bipolar voltage of ±500 kilovolts. Although not the first 500 kV HVDC project in operation (the ±533 kV Cahora Bassa scheme having been completed in 1977) it was the first such scheme to use only a single twelve-pulse bridge per pole. Consequently, its thyristor valves were the highest-rated in the world (in terms of voltage) at the time and remained so until the completion, in 2007, of the ±450 kV, single-converter NorNed scheme. The thyristor valves for Inga Shaba had 258 thyristors in series in each valve and were air-insulated and air-cooled.