31 January 2013 – The rectifier business unit of ABB South Africa recently audited four of its thyristor rectifier plants. These were installed for the Skorpion project at Namzinc 10 years ago. Namzinc purchased four ABB rectifiers in 2002, each rated 55kA 370Vdc.
The rectifier equipment is used to convert the 66kV incoming supply to 370Vdc at a total design current rating of 220kA for the electro-winning process to purify Zinc. The total power conversion involved is 82 MW. The original order involved the design, supply and installation of all components required for the power conversion, including transformers, rectifiers, control systems, heat exchangers, 66kV switchgear and 55kA dc isolators.
After 10 years of operation, ABB was approached to do an audit and some training on this equipment at Namzinc. The typical guarantee is that the rectifiers will deliver to within 1.0% of the rated current. However on inspection of the Namzinc rectifiers, all four of them were still found to be running at within 0.5% of the original specification, and that after 10 years of operation. They have been excellently maintained, and there has been no deterioration of the output or the condition of any of the four machines since installation.
The records of the Namzinc dc power supply show high plant availability. ABB South Africa has an installed base of over 60 high current rectifiers in South and southern Africa, most of these designed and manufactured locally and supported after commissioning from offices in South Africa Zambia and DRC.
A further 170 units have been supplied out of the South African factory world-wide, with output power ranging from 50kW to 8.0 MW.