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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is lower that the grounding impedanceof the machine. This can be difficult forpumps.2f Make a direct ground connectionbetween the motor and load motor.3. Lower the IGBT switching frequency.4. Modify the inverter waveform, 60° AVM vs.SFAVM.5. Install a shaft grounding system or use anisolating coupling.6. Apply conductive lubrication.7. Use minimum speed settings if possible.8. Try to ensure the line voltage is balanced toground. This can be difficult for IT, TT, TN-CS orGrounded leg systems.9. Use a dU/dt or sine-wave filter.3.2.7 HarmonicsElectrical devices with diode rectifiers, such as fluorescentlights, computers, copiers, fax machines, various laboratoryequipment and telecommunications systems, can addharmonic distortion to a mains power supply. Frequencyconverters use a diode bridge input, which can alsocontribute to harmonic distortion.The frequency converter does not draw current uniformlyfrom the power line. This non-sinusoidal current hascomponents that are multiples of the fundamental currentfrequency. These components are referred to as harmonics.It is important to control the total harmonic distortion onthe mains supply. Although the harmonic currents do notdirectly affect electrical energy consumption, they generateheat in wiring and transformers and can affect otherdevices on the same power line.3.2.7.1 Harmonic AnalysisVarious characteristics of a building’s electrical systemdetermine the exact harmonic contribution of theconverter to the THD of a facility and its ability to meetIEEE standards. Generalisations about the harmonic contri-bution of frequency converters on a specific facility isdifficult. When necessary, perform an analysis of thesystem harmonics to determine equipment effects.A frequency converter takes up a non-sinusoidal currentfrom mains, which increases the input current IRMS. A non-sinusoidal current is transformed by means of a Fourierseries analysis and split up into sine-wave currents withdifferent frequencies, i.e. different harmonic currents INwith 50 Hz or 60 Hz as the fundamental frequency.The harmonics do not affect the power consumptiondirectly, but increase the heat losses in the installation(transformer, inductors, cables). Consequently, in powerplants with a high percentage of rectifier load, harmoniccurrents should be kept at a low level to avoid overload ofthe transformer, inductors, and cables.Abbreviation Descriptionf1 fundamental frequencyI1 fundamental currentU1 fundamental voltageIn harmonic currentsUn harmonic voltagen harmonic orderTable 3.9 Harmonics-related AbbreviationsFundamentalcurrent (I1)Harmonic current (In)Current I1 I5 I7 I11Frequency[Hz]50 250 350 550Table 3.10 Transformed Non-sinusoidal CurrentCurrent Harmonic currentIRMS I1 I5 I7 I11-49Input current 1.0 0.9 0.4 0.2 < 0.1Table 3.11 Harmonic Currents Compared to the RMS InputCurrent175HA034.10Illustration 3.3 Intermediate Circuit CoilsNOTICESome of the harmonic currents can disturb communi-cation equipment connected to the same transformer orcause resonance in connection with power-factorcorrection capacitors.To ensure low harmonic currents, the frequency converteris equipped with passive filters. DC-coils reduce the totalharmonic distortion (THD) to 40%.The voltage distortion on the mains supply voltagedepends on the size of the harmonic currents multipliedby the mains impedance for the frequency in question.The total voltage distortion (THD) is calculated on the basisof the individual voltage harmonics using this formula:THD =U 25 +U 27 + ... +U 2NU1System Integration Design GuideMG20N602 Danfoss A/S © 09/2014 All rights reserved. 473 3