Engineering & Mining Journal

MAR 2013

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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MINE POWER with a multi-unit generator setup, generator-powered electric rope shovels require additional systems to dissipate regenerated energy because they can't feed electricity back into the power grid. Cat's off-grid power strategy stems from the fact that, because most mines are located in remote areas, it's common for the nearest power infrastructure to be extremely distant. Mines often plan to break ground at the pit prior to having permanent power infrastructure installed, necessitating the adoption of temporary power solution options at additional expense. Under those circumstances, electric rope shovel customers typically employ diesel-powered loading tools as an interim solution until power is established at the mine. Caterpillar's off-grid power system, however, affords mining operations the opportunity to use electric rope shovels at the onset of production in a greenfield mine, or to quickly move into a new area at an existing mine in which a stable power supply isn't readily available. Using 'ultra-capacitor' technology, the off-grid system stores regenerative energy created during swing deceleration and bucket lowering, then uses that power during periods of high demand to reduce the generator load cycle. This innovative technology, currently being validated at the Caterpillar proving grounds in Arizona, is expected to be commercially available in late 2013. Cat offered introductory details of the off-grid system at its MINExpo 2012 preshow press event, but has since been relatively silent about the technology as it fine-tunes the system prior to commercial introduction. Recently, however, Ken Banks, new-product introduction manager for Cat's electric rope shovels, provided E&MJ; with an update that clarifies some aspects of its capabilities. And, readers should note that Cat will present the latest information on this technology at Mining Media's 2013 Haulage & Loading Conference, May 19‒22 in Phoenix, Arizona, USA. E&MJ;: When using the Cat off-grid power supply, will a 4-MW genset handle peak power demand of a 7495 or 7495 HF? If not, give an example of a situation where it would not meet peak demand or where you would not recommend use of the off-grid power supply. Banks: Generally, 4 MW of genset output coupled with our peak-shaving technology will meet demand from any 7495 model rope shovel. However, at mines operating in extreme temperatures or high altitudes, genset output could be derated. Caterpillar has tightly coupled the rope shovel and gensets to provide the required output needed in all applications. We are able to offer our customers a complete and exclusive Cat solution. The peak-shaving technology also provides power management benefits to mining operations that are operating on an electrical grid. This technology configuration reduces peak power requirements on the power distribution system, allowing rope shovel customers the opportunity to reduce costs with smaller substations. The lower peak power requirements also allow smaller-gauge trail cables, or longer trail cable runs, which can also reduce costs and minimize downtime. E&MJ;: Will Caterpillar offer both onboard and offboard systems? Banks: The Caterpillar off-grid power system will have energy storage components integrated onboard the rope shovel, which is currently the most cost-effective solution. Additionally, the onboard solution allows for greater mobility and more manageable machine moves. The offboard system was used for proof of concept testing only. E&MJ;: How many ultracapacitors are used in a system, and what is the anticipated life expectancy of those components? Banks: The quantity of ultracapacitors is dependent on genset requirements, as well as to optimize capacitor life and machine performance. Ultracapacitors have proven long life in high dynamic load applications, making them the ideal energy storage device for this application. E&MJ;: Is the ultracapacitor technology the same as that used in the 6120B H FS? If not, how does it differ? Banks: The 7495 and 6120B H FS both use proven ultracapacitor technology. In shovel applications, ultracapacitors store regenerated power fromthe shovel and then draw on that energy during periods of high demand and rapid load changes. E&MJ;: Can the operator feel any differences in machine operation when using the off-grid power supply versus line power? Banks: The operator's experience, whether off or on-grid, will be exactly the same. The rope shovel will operate at full productivity, as the Cat off-grid power solution does not alter or derate any functions of the shovel. E&MJ;: What level of cost savings are possible using the off-grid solution? Cat says the high power density of the new C175-20 generator set provides more power from a smaller footprint. A single 4-MW C175-20 represents a 55% reduction in footprint when compared with two 2-MW 3516B generator sets and a 28% reduction when compared with a 4-MW 3612. www.e-mj.com MARCH 2013 • E&MJ; 61

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