Danfoss VLT AHF005 Design Manual

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Danfoss VLT AHF005 Design Manual Manual pdf 12 page image

limits based on these planning levels is described. G5/4 is asystem level standard.For 400V the voltage THD planning level is 5% at the PCC.Limits for odd and even harmonics in 400V systems are givenin Table 2 in the standard. An assessment procedure for theconnection of non-linear equipment is described. Theprocedure follows three stages, aiming to balance the levelof detail required by the assessment process with the degreeof risk that the connection of particular equipment will resultin unacceptable voltage harmonic distortion.Compliance of a system containing VLT® frequencyconverters depends on the specific topology and populationof non-linear loads. AHF can be employed to meet therequirements of G5/4.3.3 Harmonic MitigationTo mitigate the harmonics caused by the frequencyconverter 6-pulse recitifier several solutions exist and they allhave their advantages and disadvantages. The choice of theright solution depends on several factors:• The grid (background distortion, mains unbalance,resonance and type of supply - transformer/generator)• Application (load profile, number of loads and loadsize)• Local/national requirements/regulations (IEEE519,IEC, G5/4, etc.)• Total cost of ownership (initial cost, efficiency,maintenance, etc.)IEC standards are harmonized by various countries or supra-national organizations. All above mentioned IEC standardsare harmonized in the European Union with the prefix “EN”.For example the European EN 61000-3-2 is the same as IEC61000-3-2. The situation is similar in Australia and NewZealand, with the prefixes AS/NZS.Harmonic solutions can be divided into two main categories:passive and active. Where the passive solutions consist ofcapacitors, inductors or a combination of the two in differentarrangements.The simplest solution is to add inductors/reactors of typically3% to 5% in front of the frequency converter. This addedinductance reduces the amount of harmonic currentsproduced by the drive. More advanced passive solutionscombine capacitors and inductors in trap arrangementspecially tuned to eliminate harmonics starting from e.g. the5th harmonic.The active solutions determine the exact current that wouldcancel the harmonics present in the circuit and synthesizesand injects that current into the system. Thus the activesolution can mitigate the real-time harmonic disturbances,which makes these solutions very effective at any loadprofile. To read more about the Danfoss active solutions LowHarmonic Drive (LHD) or Active Filters (AAF) please see MG.34.OX.YY and MG.90.VX.YY.Introduction to Harmonics a... AHF005/010 Design GuideMG.80.C4.02 - VLT® is a registered Danfoss trademark 113 3