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Adjustable Frequency DrivesCPX9000 Drives36.7Application DescriptionDesigned to exceed the IEEE519-1992 requirements forharmonic distortion, theCPX9000 is the clear choiceWhat Are Harmonics?for applications in the water,wastewater, HVAC, industrialand process industries whereharmonics are a concern.Take a perfect wave with a fundamental frequency of 60 Hz,which is close to what is supplied by the power company.Perfect WaveVolts(v)Time(t)f(x) = sin(x)Add a second wave that is five times the fundamental frequency—300 Hz (typical of frequency added to the line by a fluorescent light).Second WaveVolts(v)Time(t)f(x) = sin(5x)5Combine the two waves. The result is a 60 Hz supply rich infifth harmonics.Resulting SupplyVolts(v)Time(t)f(x) = sin(x) +sin(5x)5What Causes Harmonics?Harmonics are the result ofnonlinear loads that convertAC line voltage to DC.Examples of equipment thatare non-linear loads are listedbelow:●AC variable frequencydrives● DC drives● Fluorescence lighting,computers, UPS systems●Industrial washingmachines, punch presses,welders, etc.How Can Harmonics Due toVFDs Be Diminished?By purchasing Eaton’s18-pulse CPX9000 drivethat is guaranteed to meetIEEE Std. 519-1992 HarmonicDistortion Limits.What Are Linear Loads?Linear loads are primarilydevices that run across theline and do not addharmonics. Motors are primeexamples. The downside tohaving large motor linearloads is that they draw moreenergy than a VFD, becauseof their inability to controlmotor speed. In mostapplications, there is a turndown valve used with themotor that will reduce theflow of the material, withoutsignificantly reducing the loadto the motor. While thisprovides some measure ofspeed control, it is extremelyinefficient.Why Be ConcernedAbout Harmonics?1. Installation and utilitycosts increase.Harmonics causedamage to transformersand lower efficienciesdue to the IR loss. Theselosses can becomesignificant and can havea dramatic effect on theHVAC systems that arecontrolling thetemperatures of thebuilding where thetransformer and driveequipment reside.2. Downtime and loss ofproductivity.Telephones and datatransmissions links maynot be guaranteed towork on the same powergrids polluted withharmonics.3. Downtime andnuisance trips of drivesand other equipment.Emergency generatorshave up to three timesthe impedance that isfound in a conventionalutility source. Thus theharmonic voltagedistortion can be upto three times as large,causing risk of operationproblems.4. Larger motors must beused. Motors runningacross the line that areconnected on pollutedpower distribution gridscan overheat or operateat lower efficiency dueto harmonics.5. Higher installationcosts. Transformers andpower equipment mustbe oversized toaccommodate the loss ofefficiencies. This is dueto the harmonic currentscirculating through thedistribution withoutperforming useful work.363636363636363636363636363636363636363636363636363636363636Volume 6—Solid-State Motor Control CA08100007E—April 2011 www.eaton.comV6-T36-193