Maputo — The normal export of electricity from the Cahora Bassa dam on the Zambezi to South Africa has been re-established, according to a Sunday press release from the dam operating company, Hidroelectrica de Cahora Bassa (HCB).

HCB had run into severe problems with the breakdown of smoothing reactors.

In direct current systems, a smoothing reactor is used to “smoothen” the direct current wave shape to reduce power losses and improve system performance. In October 2010, one of the smoothing reactors at the converter station in the dam town of Songo suffered a major breakdown.

A spare reactor was on site, but it too broke down on 24 July this year.

HCB already had a plan to refurbish the converter station, but this will only begin in April 2013. Without the reactor, HCB’s capacity to send power southwards to its main client, the South African electricity company Eskom, was severely curtailed.

Eskom itself had a spare smoothing reactor, and HCB negotiated for this to be sent by road to Cahora Bassa. The reactor weights 150 tonnes, and thus special vehicles were used to transport it slowly through Zimbabwe, and then across Mozambique’s Tete province to reach Songo.

The route was chosen to avoid taking the enormous load over many bridges.

Engineering work was needed when crossing the Mazoe river, just north of the Zimbabwean border, where a provisional dike was installed.

According to HCB, the full power supply to South Africa was restored after tests proved that the smoothing reactor was fully operational. The equipment was installed and tested by HCB’s own staff, accompanied by technicians from the German company Siemens, which built the reactor.

The release noted that, when the July breakdown occurred, HCB was already in negotiations with the Swiss multinational, ABB, over a contract for the partial rehabilitation of the Songo Converter Station. This contract envisages the acquisition of two new smoothing reactors, using modern technology and three new converter-transformers.

The negotiations were closed on 16 August, and the new equipment ordered should arrive as from February 2013. The weight of these components means that transporting them to Songo will again be a logistically complicated task. The rehabilitation of the converter substation should be completed in 2014, at a total cost of about 50 million dollars, paid entirely from HCB’s own funds.