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

Contents

10.16 Harmonics OverviewNon-linear loads such as found with drives do not drawcurrent uniformly from the power line. This non-sinusoidalcurrent has components which are multiples of the basiccurrent frequency. These components are referred to asharmonics. It is important to control the total harmonicdistortion on the mains supply. Although the harmoniccurrents do not directly affect electrical energyconsumption, they generate heat in wiring andtransformers that can affect other devices on the samepower line.10.16.1 Harmonic AnalysisSince harmonics increase heat losses, it is important todesign systems with harmonics in mind to preventoverloading the transformer, inductors, and wiring. Whennecessary, perform an analysis of the system harmonics todetermine equipment effects.A non-sinusoidal current is transformed with a Fourierseries analysis into sine-wave currents at differentfrequencies, that is, different harmonic currents IN with50 Hz or 60 Hz as the basic frequency.Abbreviation Descriptionf1 Basic frequency (50 Hz or 60 Hz)I1 Current at the basic frequencyU1 Voltage at the basic frequencyIn Current at the nth harmonic frequencyUn Voltage at the nth harmonic frequencyn Harmonic orderTable 10.26 Harmonics-related AbbreviationsBasiccurrent (I1)Harmonic current (In)Current I1 I5 I7 I11Frequency 50 Hz 250 Hz 350 Hz 550 HzTable 10.27 Basic Currents and Harmonic CurrentsCurrent Harmonic currentIRMS I1 I5 I7 I11-49Input current 1.0 0.9 0.5 0.2 <0.1Table 10.28 Harmonic Currents Compared to the RMS InputCurrentThe voltage distortion on the mains supply voltagedepends on the size of the harmonic currents multipliedby the mains impedance for the frequency in question. Thetotal voltage distortion (THDi) is calculated based on theindividual voltage harmonics using this formula:THDi = U25 + U27 + ... + U2nU10.16.2 Effect of Harmonics in a PowerDistribution SystemIn Illustration 10.19, a transformer is connected on theprimary side to a point of common coupling PCC1, on themedium voltage supply. The transformer has an impedanceZxfr and feeds several loads. The point of common couplingwhere all loads are connected is PCC2. Each load connectsthrough cables that have an impedance Z1, Z2, Z3.PCC Point of common couplingMV Medium voltageLV Low voltageZxfr Transformer impedanceZ# Modeling resistance and inductance in the wiringIllustration 10.19 Small Distribution SystemHarmonic currents drawn by non-linear loads causedistortion of the voltage because of the voltage drop onthe impedances of the distribution system. Higherimpedances result in higher levels of voltage distortion.Current distortion relates to apparatus performance and itrelates to the individual load. Voltage distortion relates tosystem performance. It is not possible to determine thevoltage distortion in the PCC knowing only the harmonicperformance of the load. To predict the distortion in thePCC, the configuration of the distribution system andrelevant impedances must be known.Electrical Installation Con... VLT® AQUA Drive FC 20296 Danfoss A/S © 05/2017 All rights reserved. MG22B1021010