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Send  Share  RSS  Twitter  09 Oct 2009

: New Power Supply for Freezing Mine

 





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When temperatures reach as low as minus 27 degrees Celsius in this snow-swept landscape many would assume that this is a location in some far flung region of the northern hemisphere, but for Lesotho’s Letseng Diamond Mine this is the norm during the most severe winter periods.

It’s an unusual mine for many reasons. Firstly because Letseng is believed to be the world’s highest diamond operation at over 3 200m, but also because of the amazing gems this mine has yielded since it was first discovered back in 1957 – home to the world famous Lesotho Promise, a 603 carat gemstone of remarkable quality, and its famed predecessor, the 601 carat Lesotho Brown (named for its distinctive colour).

Mining at this remote site, owned jointly by Gem Diamonds (70%) and the Kingdom of Lesotho (30%), is continuous, running 365 days a year, 24/7, making sustainable energy supply and management a critical issue. In this mountain Kingdom, this responsibility falls on the Lesotho Electrical Corporation (LEC), deriving its power from the Lesotho Highlands Water Scheme’s hydroelectric programme and supplemented by South Africa’s power utility, Eskom.

Some three years ago, Letseng employed the services of Barloworld Power to install two Cat generator sets to address emergency standby power requirements. However, these units were never intended to supply power to run the mine’s two DMS plants and an additional solution was needed as a contingency plan. Each month around 450 000t of kimberlite ore is fed through these plants and even a power outage of just five minutes can create chaos when pumps shutdown and hoppers and conveyors need to be cleared.

Subsequently the order for a supply of five 1 000 kVA Cat containerised gensets was placed, each powered by a 597kW Cat C32 ACERT engine, which will supply prime power to run Plant 1 during an LEC shutdown. During unplanned power interruptions, these units start automatically in a synchronised fashion, supplying prime power within 80 seconds. In addition to full automatic operation, they can also be started manually in parallel to the LEC supply during planned maintenance outages.

Barloworld Power’s Whitey Visser, Business Manager: Design and Engineering Centre of Excellence comments: “In terms of the extreme weather conditions, altitude, logistics and the mine’s remote location, this has been one of the most exciting and challenging projects undertaken by the company. Being a turnkey solution, Barloworld Power was responsible for all civil, electrical and mechanical designs, procurement, manufacturing, testing, installations, commissioning and management of the alternative power generation substation and control building. The physical civil work was the only part of the project executed by the mine.”

“We also implemented a few modifications. We replaced the standard controllers, which enabled us to synchronise these Cat units to the grid for parallel operation and seamless transfer. There were also modifications to the SA canopies and fuel lines,” Visser continues.

Four independent simulation tests were carried out to test the new system. Each time, the mine came off the grid and the five Cat engines started up instantly, simultaneously emitting a brief but distinctive streak of black diesel smoke from their external exhausts. And on each occasion a seamless transfer of power was achieved with zero interruption to production activities at Plant 1.


 
 
 
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