Danfoss VLT Refrigeration Drive FC 103 Design Manual

Also see for VLT FC 103: Service guide Installation guide Installation guide Operating guide Installation guide

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Danfoss VLT Refrigeration Drive FC 103 Design Manual Manual pdf 49 page image

The negative effect of harmonics is 2-fold• Harmonic currents contribute to system losses (incabling, transformer).• Harmonic voltage distortion causes disturbanceto other loads and increase losses in other loads.Non-linearCurrent VoltageSystemImpedanceDisturbance toother usersContribution tosystem losses130BB541.10Illustration 3.5 Negative Effects of Harmonics3.2.7.5 Harmonic Limitation Standards andRequirementsThe requirements for harmonic limitation can be:• Application-specific requirements.• Standards that must be observed.The application-specific requirements are related to aspecific installation where there are technical reasons forlimiting the harmonics.ExampleIf 1 of the motors is connected directly online and theother is supplied through a frequency converter, a 250 kVAtransformer with 2 110 kW motors connected is sufficient.If both motors are frequency converter supplied, however,the transformer is undersized. Using more means ofharmonic reduction within the installation or selecting lowharmonic drive variants makes it possible for both motorsto run with frequency converters.There are various harmonic mitigation standards,regulations, and recommendations. Different standardsapply in different geographical areas and industries. Thefollowing standards are the most common:• IEC61000-3-2• IEC61000-3-12• IEC61000-3-4• IEEE 519• G5/4See the VLT® Advanced Harmonic Filter AHF 005/AHF 010Design Guide for specific details on each standard.In Europe, the maximum THDv is 8% if the plant isconnected via the public grid. If the plant has its owntransformer, the limit is 10% THDv. The VLT® RefrigerationDrive FC 103 is designed to withstand 10% THDv.3.2.7.6 Harmonic MitigationIn cases where extra harmonic suppression is required,Danfoss offers a wide range of mitigation equipment.These are:• 12-pulse drives.• AHF filters.• Low harmonic drives.• Active filters.The choice of the right solution depends on severalfactors:• The grid (background distortion, mainsunbalance, resonance, and type of supply(transformer/generator).• Application (load profile, number of loads, andload size).• Local/national requirements/regulations (IEEE 519,IEC, G5/4, and so on).• Total cost of ownership (initial cost, efficiency,maintenance, and so on).Always consider harmonic mitigation if the transformerload has a non-linear contribution of 40% or more.Danfoss offers tools for calculation of harmonics, seechapter 2.8.2 PC Software.3.2.8 Ground Leakage CurrentFollow national and local codes regarding protectiveearthing of equipment where leakage current exceeds 3.5mA.Frequency converter technology implies high frequencyswitching at high power. This generates a leakage currentin the ground connection.The ground leakage current is made up of several contri-butions and depends on various system configurations,including:• RFI filtering.• Motor cable length.• Motor cable screening.• Frequency converter power.System Integration Design GuideMG16G202 Danfoss A/S © 08/2015 All rights reserved. 473 3