Wade Walker, one of the largest electrical, control and instrumentation (EC&I) contractors in mining, has successfully completed a significant 95,000 man-hour contract for the supply and installation of electrical equipment and instrumentation in preparation for the new tailings preparation and distribution facility at Gold Fields’ South Deep gold mine. The project is part of the mine’s extensive capital development and construction program to achieve a production rate of between 750,000 and 800,000 oz/y of gold by the end of 2014. South Deep is a fully mechanised gold mine with one of the deepest orebodies in the world.Michael Spear, Project Manager at Wade Walker, says the contract is one of two awarded to the company for work at the mine. The second contract, with early involvement for constructability during the detailed design phase, comprises the supply of electrical equipment and instrumentation to upgrade the mine’s backfill preparation plant capacity.
“We were awarded the tailings facility contract against a large number of other bidders in a competitive process administered by Gold Fields Shared Services. We believe that our competitive pricing, our reputation for delivering quality work and our extensive experience in the mining industry were factors that were likely to have played a role in Wade Walker securing the contract,” Spear says.
One of the challenges for Wade Walker was the comprehensive scope of work included in the contract for the tailings facility expansion – from the supply and installation of equipment to distribute medium voltage (MV) power to four substations at disparate locations on the mine.
Wade Walker supplied and installed the ring main units, transformers, MCCs, lighting distribution boards, pressurisation fans inside the substations, inline instruments and process instruments.
Spear says electrical power was drawn from the existing MV power supply substation at the gold plant and reticulated to the slimes dam pump station, the return water plant and the neutralisation facility.
An 11 kV electrical line was erected from the gold plant to the return water pump station, a distance of 6.7 km. The surveying of the power line route, which crossed over privately owned farms and as well as mine land, was undertaken by Wade Walker as part of the contract.
“We installed the MV lines on 11 m concrete poles but had to deviate from the original design at two locations: 15 m poles were used where the lines cross the public road to Fochville and 13 m poles were used to carry the MV lines over existing 11 kV Eskom lines.
“A decision was made by the Gold Fields engineers to install an OPGW cable in which the earth and the fibre optic cores are incorporated into one cable. This solution offers less maintenance and better protection. We also had to connect the fibre optics and supply fibre optic patch panels.’
Spear points out that Wade Walker technical staff are regularly updated and trained on new technological advances. Thus, the company has extensive experience in the field of fibre optics and was able to implement the changed requirements.
“Fibre optics will be used in the tailings plant upgrade to facilitate control communication between the gold plant and the return pump station. We also supplied the programmable logic controllers (PLCs) which tied into the network of the fibre optic installation.”
The installation of a small MCC and variable speed drives (VSDs) that feed three spindle pumps presented no difficulties. The challenge lay in coordinating within the project deadline the importation and installation of an enclosed transformer to coincide with the completion of the building of the substation.
“Our experience in overcoming logistical issues on projects in various parts of Africa gave us the edge in dealing with obstacles to meet a tight deadline,” Spear says. “Ongoing liaison with the electrical system designers and the overall project managers was key.”
A decision by the Gold Fields engineers to standardise on 220 V motors for pressurisation fans installed in substations led to an adaptation requirement during work on the low voltage (LV) portion of the contract.
“We were able to adapt the fans from 525 V running off the MCC to 220 V running off the distribution board. We had to replace the motors in the fans and also supply stop-start panels. The additional work was undertaken without impacting on the delivery time frame.”
An unusual aspect of the tailing facility contract for Wade Walker related to the supply of a density transmitter powered by a nuclear source. “Apart from arranging the importation of the instrument we interfaced with various government departments because of health and safety requirements relating to the use of this type of equipment.”
A demanding task from an installation perspective arose with the fixing of a 185 mm three core XLPE MV cable on racking 6 to 8 m high between the gold plant substation, through the operating plant to the new tailings facility gold plant substation. The cable was rolled out on two 500 metre lengths of scaffolding and then lifted and fixed by hand onto the racking.
The project was completed in July 2011, and finished with an excellent safety record without any significant injury, lost time or otherwise.