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BEARINGS, BELTS & CHIAINS identification of potential problems. > Remedial action The most effective preventative or remedial action in the event of electrical erosion in bearings will depend on the characteristics of the equipment and on the interventions available to the engineer. In new installations, risks can be minimised by using symmetrical multi-core motor cables in which the earth conductor is either arranged as a concentric shield around the phase leads or as three separate leads positioned between them. Shielded motor cables can also provide a short, lowimpedance path for commonmode current to return to the inverter. Likewise, a grounding brush on the motor shaft can offer an easier path to earth than that provided by the motor bearings. Effective grounding between other motor components can also be important. The high-frequency switching that can be a major cause of electrical erosion can sometimes be minimised by changing the characteristics of the drive control program, or by installing dedicated filters in the drive circuit. The use of bearings with insulating housings can eliminate the electrical pathway through the motor bearings, thus preventing erosion. Insulated bearings are readily available, but different coatings and bearing designs have different characteristics when exposed to highfrequency AC currents. Bearing manufacturers have tested their proprietary designs under a wide range of operating conditions and can offer advice on the most suitable bearings for particular applications. In some cases, bearings with ceramic rolling elements can be particularly useful, providing perfect electrical insulation between a motor’s stator and rotor. D&C Solar plant uses plain bearings to track the sun More than 1,000 precision plain bearing rod ends are playing a key role in the world’s largest parabolic trough solar power station – the 50MW Andasol 1 plant in southern Spain The €300m plant, which went on line in mid- 2009, is expected to generate about 180GWh a year – supporting the power needs of more than 200,000 people, and saving around 150,000 tonnes of carbon dioxide. It is the first of three similar plants being built at the site in Andalusia. The plant consists of three main parts, the largest being an array of solar troughs with a collector area of more than 510,000m 2 – equivalent to around 70 soccer pitches. There is also a power plant area and a heat accumulator, which allows the station to continue generating electricity even in cloudy weather or after sunset. The solar field consists of parallel rows of parabolic collectors arranged on a north-south axis to follow the path of the sun from east to west. To track the sun, each collector is fitted with a hydraulic drive. The trough-shaped parabolic mirrors focus the solar radiation onto an absorber pipe, positioned along the collector’s focal line. A closed-circuit pipe system uses synthetic oil to transfer heat at up to 400°C. The heated oil is pumped to a power block where it flows through a heat exchanger. The next stage is similar to the steam cycle in a conventional power plant – the steam generated in the heat exchanger drives a turbine connected to a generator. The steam then condenses back into water, which is recirculated. A total of 1,248 Elges hydraulic rod end bearings supplied by Schaeffler support the solar troughs, positioning them with millimetre precision to follow the sun. “High-precision bearings are required so that the power plant can operate at maximum efficiency,” explains Dr Arndt Schweigert, head of Schaeffler’s power generation sector. “Moreover, the bearings also have to withstand loads that should not be underestimated.” The plain bearings have been optimised for the slow, precise swivel motion. It is critical that these movements are smooth, without any stick-slip effects or jolting on start-up. At the same time, the hydraulic rod ends need to support high forces and to handle alternating loads. This allows the 150m-long chains of collectors to be adjusted to within a tenth of a millimetre. The rod ends are fitted with manganese phosphate-coated radial spherical plain bearings with steel-to-steel sliding contact surfaces. The Parabolic reflectors focus the sun’s energy on a pipe carrying oil which is heated to 400°C surface treatment improves the running-in characteristics and reduces friction. The inner ring of the spherical plain bearing is 70mm wide and has a 110mm cylindrical bore diameter, as well as a spherical outer slideway. The 160mmdiameter outer ring has a cylindrical outer surface and a concave inner slideway with a diameter of 140mm. Schaeffler has also provided 7,488 lead-free plain bearing strips for the Andasol plant. These are mounted in the supports between the individual segments of the 150m-long collector chains, ensuring smooth slewing movements while tracking the sun. 30 November/December 2010 www.drives.co.uk
PARTNERSHIP BASED ON TRUST – AND TRUST BASED ON QUALITY. Total Quality by NSK: HPS TM spherical roller bearings. NSK’s compact HPS TM spherical roller bearings set new standards for precision and performance. This new generation of bearings extends maintenance intervals considerably and reduces equipment downtime at high speeds and in extreme conditions with wide temperature variations, wet and dusty environments. More about NSK at www.nskeurope.com or call us on +44 (0) 1636 605123 NSK UK Ltd · Northern Road, Newark, Nottinghamshire, NG24 2JF · Telephone +44 (0) 1636 605123 · info-uk@nsk.com
Page 1 and 2: DRIVES & CONTROLS www.drives.co.uk
Page 3 and 4: VLT® Decentral Drive FCD 302 I VLT
Page 5 and 6: DRIVES & CONTROLS Editor Tony Sacks
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Page 9 and 10: more than just a pretty interface.
Page 12 and 13: Mechanical drives factory moves to
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Page 18 and 19: TECHNOLOGY Motor-mounting drives
Page 20: TECHNOLOGY IN BRIEF The OPC Foundat
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Page 25 and 26: elsewhere; and • restoring system
Page 27 and 28: LINEAR MOTION Museum’s 4D ride ha
Page 29 and 30: Application Door closer mechanism f
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Page 33: Bearing up to electrical erosion Va
Page 37 and 38: Your life in our hands. INDUSTRIAL
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Page 44 and 45: PLCs AND HMIs method and the sealin
Page 46 and 47: Experience is our Strength )))!&'$"
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Page 50 and 51: GAMBICA VIEWPOINT Taking the open r
Page 52 and 53: Sponsored column No. 3 November/Dec
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Page 56 and 57: SENSORS Cable extension sensors hav
Page 58: CONTROL CNC offers a choice of driv
Page 61 and 62: DRIVES AND CONTROLS EXHIBITION 2010
Page 63 and 64: 1 HPMG Hangzhou Permanent Magnet Gr
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