In case of a single line failure, transmission with reduced power is possible via the surviving pole and return through the earth.

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.

Significant commercial hurdles, culminating in hearings at an International Arbitration Tribunal seated in Lisbon, in 1988, also had to be overcome.

Equipment was constructed and supplied by ZAMCO, which was a consortium of AEG-Telefunken JV, Brown Boveri Company, and Siemens AG of Germany.

The only other HVDC scheme in the world equipped in this way from the outset was the first phase – now decommissioned – of the Shin Shinano frequency converter in Japan.

Phases 2 and 3 used improved thyristors with a rating of 2.4 kV each and only required 192 in series per valve – still a large number by modern standards – with two in parallel.

Subsequently, Eskom has commenced electricity supply to Mozambique at 400 kV, under terms similar to the original wheeling agreement, from the Arnot Power Station in Mpumalanga, via Swaziland.

The principal purpose of this infrastructure is to provide bulk electricity supplies to the Mozal Aluminium Smelter operated by BHP.

The Memorandum of Understanding, signed on 2 November 2007, means that Mozambique will by the end of 2007 be in charge of a project located on its soil but on which it had no control for the past 30 years due to contractual obligations with Portugal.

Mozambique will, however, need to pay US$950 million to the Portuguese government as compensation for the post civil-war reconstruction and maintenance of the dam.

The civil war resulted in serious damage to the transmission infrastructure, forcing the Portuguese government to pay about US$2.5 billion out of pocket to repair it.