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PLANT DESIGN • By eliminating a series of mechanical and electrical components, availability automatically increases. • Drive stations with a gearless drive system can be built more compactly. This is especially useful for drive stations in tunnels or underground applications. • The capability to increase drive power per drive pulley enables the design of longer belt conveyor systems, and the number of drive and transfer stations can be reduced. • The efficiency of the entire system increases by 3%–4%. • The maintenance needs of the drive system are also lower. Gear maintenance activities alone account for up to 5% of the original investment costs. • Fewer spare parts, and as a result lower inventories, lead to lower expenses. • Noise levels are lower with the elimination of high-speed mechanical components. With gearless drive systems, a lowspeed synchronous motor replaces the high-speed asynchronous motor, gearboxes and couplings. The motor's rotor is flanged directly to the shaft of the drive pulley, thus eliminating gearboxes, couplings and the associated lubrication and cooling systems. The motor also does not require motor bearings. Compared with conventional solutions, in which the drives have to be mounted on both sides of the drive pulley for larger power requirements, only one gearless drive has to be mounted, and on just one side. This allows better access for maintenance as well as shorter installation and commissioning times. Converter technology, said Siemens, enables gearless drives to be adjusted more efficiently to the individual requirements and the operating conditions of the belt conveyor. Converters, power distribution and the respective automation technology are completely installed in a container module (ehouse), tested and transported to the point of installation. Due to the high degree of pre-installation and pre-commissioning, they can be quickly installed and commissioned. A diagnostic system as well as applications for monitoring production data and remote maintenance provide maintenance personnel with a continuous overview of all relevant plant parameters. For downhill conveyors, depending on the mode of operation and the geographic situation, the drives can switch between motor and generator operation and thus produce additional energy. With the drive control, acceleration is gentle and smooth—protecting bearings, belt pulleys, brakes and rolls, and avoiding belt vibration and tears. At the same time, by regulation of the performance rating, belt speed can be adapted to the current Siemens offers two types of converters, each of which has specific benefits based on the nature of the application. At Antapaccay, air-cooled Sinamics SL 150 cyclo-converters are used in the mine's gearless conveyor and mill drives. 38 E&MJ; • JULY 2013 carry volumes of the conveyor and thus increase the conveyor's effectiveness. Siemens pointed out that it has been using gearless drives for many years, on low-speed applications for ore and cement mills, mine hoists, belt conveyors, bucketchain excavators, drag-lines, as well as for rolling mills, ships and wind-power plants. In 1986, Siemens and ThyssenKrupp (formerly O&K;) installed the first gearless drive system with a cyclo-converter and synchronous motor on a belt conveyor at Steinkohle AG's (RAG) underground Prosper-Haniel coal mine in Germany. Siemens is happy to point out that, more than a quarter-century later, the same drive systems are still in operation. The customer is still happy, considering that availability of the conveyor system has been at the 99% level or above, no significant interruptions or failures attributable to motors and converters have been reported, maintenance costs are significantly less than for conventional drives with gearboxes, and electrical energy savings of 10% are achieved annually compared with fixed speed drive systems. Antapaccay's Gearless System Antapaccay is the first copper mine in Peru where gearless drives for an overland conveyor system are being used. The mine is owned by Glencore Xstrata, which acquired the nearby Tintaya copper operation for $750 million from BHP Billiton in 2006, along with the Antapaccay and Coroccohuayco projects. Situated at an elevation of 4,200 m, the mine started commercial operation at the beginning of November 2012 and will initially produce an average of 160,000 metric tons (mt) of copper in concentrate per year, plus gold and silver by-product credits. The mine's main belt conveyor, which was installed by ThyssenKrupp Robins, transports the ore over a distance of 6.5 km from the mine to the beneficiation plant. The conveyor, featuring a belt width of 1,370 mm and a belt speed of 6.2 m/s, can transport more than 5,000 mt of material per hour. Its gearless drive system is equipped with two low-speed synchronous motors with cyclo-converters (installed power of 3.8 MW, motor speed of 63 rpm, rated torque at 576 kNm) and a motor cooling system. Load sharing between the two drives can be adjusted according to the requirements of the belt conveyor. Siemens also delivered the power distribution, the converter transformers as well as the completely pre-assembled e-house. www.e-mj.com