2nd Quarter 2011Electrical switching & drive systems & components
The installation of a large variable speed AC drive and bypass on a pump has ensured production security at a South African gold mine.
The Simmer and Jack Buffelsfontein gold mine needed to reactivate a tailings disposal system that had been out of commission. The tailings disposal system, at the very end of the process, is responsible for pumping 300 cubic metres per hour of slurry onto the tailings dam. Any interruption in slurry pumping has a knock-on effect up the line, very quickly halting production of gold. However, with an obsolete variable speed drive, reliability and availability of spares were proving to be unattainable. Control Techniques was chosen to solve this problem because of its fast turnaround time and its ability to supply a close variable speed control and bypass facility in the event of pump drive failure.
The Control Techniques Drive Centre in Gauteng has supplied many other variable-speed drives to Simmer and Jack and is a preferred drives supplier to the mine. The 220 kW drive solution chosen was a modular Unidrive SPM AC drive comprising four modules, complete with input and output chokes, a door-mounted CTIU touch-screen control panel and a direct-on-line bypass system with main circuit breaker, contactor and motor overload protection. Control Techniques designed and built the panel and supplied the control logic that allows the pump to be started either from the panel or from the remote control room.
Flowmeters measure the upstream flow of the slurry and these in turn feed into the process control system that regulates the speed setpoint for the drive. The ability to control pump speed to match the needs of the plant results in a considerable energy saving on such a big pump. In the event of drive failure or maintenance work, the customer can manually select the bypass system to ensure that pumping of the tailings, and hence gold production, continues uninterrupted.
The units that make up the Unidrive SPM range can be used to implement most types of system. The separation of the power circuit into rectifier and drive stages enables elegant and compact active input configurations to be implemented.
The modular nature of the power circuit allows drive systems to be constructed in non-standard enclosures. The range is part of the Unidrive SP ‘solutions platform’ AC variable speed drive range that spans 0,75 kW right up to 1,9 MW. It is configurable into five operating modes – open and closed loop, vector, servo and regenerating modes – and a wide range of feedback, networking and programming functions can be added with plug-in modules. Simmer and Jack Mines is a developing South African gold producer with a 34% stake in First Uranium Corporation. The company acquired the Buffelsfontein gold mine in 2005 and has recently re-opened Number Five shaft after an extensive rehabilitation project to restore the shaft to working order after it had been rendered inaccessible by a seismic event in 2005.
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