Danfoss VLT AQUA Drive FC 202 Design Manual

Also see for VLT AQUA Drive FC 202: Service guide Installation guide Installation guide Operating guide Installation guide

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Danfoss VLT AQUA Drive FC 202 Design Manual Manual pdf 54 page image

A commonly used term for describing the impedance of agrid is the short-circuit ratio Rsce, defined as the ratiobetween the short circuit apparent power of the supply atthe PCC (Ssc) and the rated apparent power of the load(Sequ).Rsce = SceSequwhere Ssc = U2Zsupplyand Sequ = U × IequThe negative effect of harmonics is two-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 losses130BB541.10Figure 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.ExampleA 250 kVA transformer with two 110 kW (150 hp) motorsconnected is sufficient if one of the motors is connecteddirectly online and the other is supplied through anadjustable frequency drive. However, the transformer isundersized if both motors are supplied by the adjustablefrequency drive. Using additional means of harmonicreduction within the installation or selecting low harmonicdrive variants makes it possible for both motors to runwith adjustable frequency drives.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 AHF 005/010 Design Guide for specific details oneach standard.In Europe, the maximum THVD is 8% if the plant isconnected via the public grid. If the plant has its owntransformer, the limit is 10% THVD. The VLT® AQUA Drive isdesigned to withstand 10% THVD.3.2.7.6 Harmonic MitigationIn cases where additional harmonic suppression isrequired, Danfoss offers a wide range of mitigationequipment. These are:• 12-pulse drives• AHF filters• Low Harmonic Drives• Active FiltersThe choice of the right solution depends on severalfactors:• The grid (background distortion, line powerunbalance, resonance and type of supply(transformer/generator).• Application (load profile, number of loads andload size).• Local/national requirements/regulations (IEEE519,IEC, G5/4, etc.).• Total cost of ownership (initial cost, efficiency,maintenance, etc.).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 protectivegrounding of equipment where leakage current exceeds3.5 mA.Adjustable frequency drive technology implies highfrequency switching at high power. This generates aleakage current in the ground connection.System Integration VLT® AQUA Drive FC 20252 Danfoss A/S © 09/2014 All rights reserved. MG20N62233