ABB MT series Installation, Operation & Maintenance Manual

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5.4 Bearing currentsInsulated bearings or bearing constructions, commonmode filters and suitable cabling and grounding methodsmust be used according to the following instructions:5.4.1 Elimination of bearing currents withABB ACS800 and ACS550 convertersIn the case of the ABB ACS800 and ACS550-seriesfrequency converter with a diode supply unit, the followingmethods must be used to avoid harmful bearing currents inthe motors:Nominal Power (Pn)and / or Frame size (IEC)Preventive measuresPn < 100 kW No actions neededPn ≥ 100 kWORIEC 315 ≤ Frame size≤ IEC 355Insulated non-drive endbearingPn ≥ 350 kWORIEC 400 ≤ Frame size≤ IEC 450Insulated non-drive endbearingANDCommon mode filter atthe converterInsulated bearings which have aluminum oxide coatedinner and/or outer bores or ceramic rolling elements,are recommended. Aluminum oxide coatings shall alsobe treated with a sealant to prevent dirt and humiditypenetrating into the porous coating. For the exact type ofbearing insulation, see the motor’s rating plate. Changingthe bearing type or insulation method without ABB’spermission is prohibited.5.4.2 Elimination of bearing currentswith all other convertersThe user is responsible for protecting the motor and drivenequipment from harmful bearing currents. Instructionsdescribed in Chapter 5.4.1 can be used as guideline, buttheir effectiveness cannot be guaranteed in all cases.5.5 Cabling, grounding and EMCTo provide proper grounding and to ensure compliancewith any applicable EMC requirements, motors above 30kW shall be cabled by shielded symmetrical cables andEMC glands, i.e. cable glands providing 360° bonding.Also for smaller motors symmetrical and shielded cablesare highly recommended. Make the 360° groundingarrangement at all the cable entries as described in theinstructions for the glands. Twist the cable shields intobundles and connect to the nearest ground terminal/busbar inside the terminal box, converter cabinet, etc.NOTE!Proper cable glands providing 360° bonding mustbe used at all termination points, e.g. at motor,converter, possible safety switch, etc.For motors of frame size IEC 280 and upward, additionalpotential equalization between the motor frame and thedriven equipment is needed, unless both are mounted ona common steel base. In this case, the high frequencyconductivity of the connection provided by the steelbase should be checked by, for example, measuring thepotential difference between the components.More information about grounding and cabling of variablespeed drives can be found in the manual “Grounding andcabling of the drive system” (Code: 3AFY 61201998).5.6 Operating speedFor speeds higher than the nominal speed stated on themotor’s rating plate or in the respective product catalogue,ensure that either the highest permissible rotational speedof the motor or the critical speed of the whole application isnot exceeded.5.7 Dimensioning the motorfor variable speed application5.7.1 GeneralIn case of ABB’s frequency converters, the motors canbe dimensioned by using ABB’s DriveSize dimensioningprogram. The tool is downloadable from the ABB website(www.abb.com/motors&generators).For application supplied by other converters, the motorsmust be dimensioned manually. For more information,please contact ABB.The loadability curves (or load capacity curves) are basedon nominal supply voltage. Operation in under or overvoltage conditions may influence on the performance of theapplication.5.7.2 Dimensioning with ABB ACS800converters with DTC controlThe loadability curves presented in Figures 4a - 4d are validfor ABB ACS800 converters with uncontrolled DC-voltageand DTC-control. The figures show the approximatemaximum continuous output torque of the motors as afunction of supply frequency. The output torque is givenas a percentage of the nominal torque of the motor. Thevalues are indicative and exact values are available onrequest.NOTE!The maximum speed of the motor must not beexceeded!EN-12 ABB Motors and Generators | Low voltage motor manual 01-2009