cahora-bassa was out of service from 1985 to 1997 because of the mozambican civil war in the region. the project was beset with technological challenges, most notable of these being the adoption of solid-state rectification devices in a large-scale commercial installation. mercury-arc valves had been the "de facto" standard for hvdc up to this time. cahora bassa was the first hvdc scheme ordered with thyristor valves, though its operation was delayed. it was also the first hvdc scheme operational in africa, and the first anywhere in the world to operate above 500 kv. significant commercial hurdles, culminating in hearings at an international arbitration tribunal seated in lisbon, in 1988, also had to be overcome.