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MOTORS & DRIVES 54 E&MJ; • APRIL 2016 www.e-mj.com FC-200 grade cast iron provides supe- rior strength and heat dissipation, while the motors are built with 4140 high- strength steel shafts. They are designed for vertical or horizontal mounting, and have exceptional high starting and break- down torque, WEG claims. As well as being fi tted to crushers of various types, these motors can also be used in applica- tions such as grizzley feeders, belt feed- ers and conveyors. The company's MVW01 variable-speed drive is designed to control medium-volt- age induction motors. It features unique innovations, combining hardware robust- ness with simplicity, reliability and safe- ty in a compact solution with few com- ponents and state-of-the-art generation technology, WEG stated. The company recently reported on a project it completed last year, involving the supply of two replacement synchro- nous mill motors for Grange Resources in Tasmania. WEG designed a motor specif- ically tailored to retrofi t with the existing infrastructure of the old motor, providing a "drop-in fi t" that allowed Grange to mount the new motors without having to redesign the existing foundations. WEG engineered the new motors and the complete excitation system panel in Brazil, with the components being manu- factured in India before being shipped to Tasmania for installation. A New Name in Drives The acquisition at the end of 2014 by Danfoss of the Finnish producer of AC drives, Vacon, led to the formation of Danfoss Drives. The company now sup- plies its VLT and Vacon drive technol- ogy for controlling mining and mineral processing equipment such as convey- ors, feeders, slurry pumps, cyclone-feed pumps, tailings pumps, fl otation cells, mine dewatering pumps and fans, crush- ers and screens, as well as large materi- al-handling machines such as excavators, stackers, reclaimers and shiploaders. The company noted that AC drives are increasingly being used to control equip- ment on mine sites effi ciently. To protect them from the harsh environment, they are often installed in sealed switchrooms, but this in turn creates challenges as the more drives there are in a room, the greater the heat loads created. While this can lead to the need for higher-capacity air-conditioning systems substations, the unique back-channel cooling design of higher power VLT drives, and the avail- ability of Vacon liquid-cooled drives can result in signifi cantly reduced heat loads in switchrooms, enabling the use of small- er, lower-cost air-conditioning systems. The sheer size of mining operations means that long cables are often need- ed between drives and motors. Both VLT and Vacon drives are designed to provide trouble-free operation with cable lengths up to at least 150 m (500 ft) for screened cables and 300 m for unscreened cables, saving space, installation time and costs compared to more traditional drive solu- tions, Danfoss pointed out. Mine ventilation is one area where AC drives can save money, since fan costs often take up a major slice of a mine's total power costs. According to Dan- foss, AC drives are well-recognized for being the most fl exible, energy-effi cient and low-maintenance method for con- trolling both main and auxiliary fans, and can easily be integrated into ventila- tion-on-demand control systems. The company cited one example where trials with a Vacon drive on one booster fan at an underground mine in Alaska produced savings that translated into around $100,000 based on the cost of on-site diesel generation, with the pay- back measured in months. The success of the trial led to the rest of the fans at the mine being equipped with Vacon drives. Bosch Rexroth Offers an Alternative With its range of Hägglunds hydraulic drives, Bosch Rexroth offers an alterna- tive approach to electric drives for some applications. For mining, these can include convey- ors, feeders, crush- ers and mills, as well as large-scale stockyard machines. Focusing on feed- ers, the company states that drive se- lection is extremely important for their function, which is to control the gravity fl ow of bulk solids. Hydraulic drives, especially of the low-speed, high-torque type, are becom- ing more widely used on apron and belt feeders, which operate under severe con- ditions where there is often the need for high starting torque as well as frequent load spikes. While still less common than electromechanical drives, these systems can now be found in installations around the world, Bosch Rexroth noted. The starting torque needed is a ma- jor factor when sizing feeder drives, with high shear forces increasing the starting torque by as much as 200% of the run- ning torque when coarse rock is being handled. Hydraulic drives allow precise limiting of the maximum torque, protect- ing the feeder belts and chains, and no drive oversizing is needed to cope with the tough feeder starts, as is the case with electromechanical drives. The company added that a further ad- vantage of hydraulic drives is their han- dling of changes and differences in run- ning speed. While small speed variations occur because of changes in material den- sity or operating commands, major slow- downs can happen as a result of changes in material fl ow, or through blockages. Hydraulic drives can run constantly at any speed, from minimum to maximum, without overheating the electric motor. In addition, they provide built-in protection against shock loads, because of the hy- draulic motor's low moment of inertia. Maintenance on hydraulic drives is also more straight-forward, since they are more compact than electromechani- cal designs and have fewer components. With a feeder needing just one electric motor and one pump, more than one drive Hydraulic drives offer benefi ts on feeders, according to Bosch Rexroth.