Energy management specialist Schneider Electric South Africa has been commissioned by gold producer Harmony Gold to upgrade the 106 Level subvertical winder at its Doornkop mine, 30 km west of Johannesburg.

Schneider Electric South Africa Drives Competence Centre GM Helgard Honiball says the current winder control is a PowerReg system, which is a slip ring motor controller with resistor controls in steps.

“As the winder is an integral part of the emergency evacuation plan of the mine, the winder control system is critical. Schneider Electric South Africa will optimise and upgrade the current control system to variable-speed drive (VSD) control and replace the motor with a more efficient squirrel cage induction machine,” he explains.

Honiball adds that, once upgraded, the VSD control will run at a unity input power factor, irrespective of the load on the motor, improving overall system efficiency. Further, it will also be able to run from a backup diesel generator.

The project, to be completed by the fourth quarter of 2011, requires Schneider Electric South Africa to design, supply and install the winder control system upgrade.

“We have a great deal of expertise in replacing systems with VSDs and Schneider Electric South Africa’s established installed base as well as its superior technology proved to be a firm motivation in Harmony selecting us to under- take this upgrade project,” states Honiball.

The Doornkop mine comprises a single-shaft system of intermediate depth, the maxi- mum depth currently reaching 1 973 m, and is serviced by the Doornkop carbon-in-pulp gold plant.

At Doornkop, both the Kimberley and South reefs are mined by means of narrow reef, conventional mining and mechanised bord-and-pillar mining. Production at the Doornkop South reef project, on which development began in the 2003 financial year and which enables access to the higher-grade South reef, started in the 2008 financial year.

The project is currently being ramped up, with full production scheduled for the 2015 financial year.