Harmonic Distortion In Electrical Systems - Trane
providing insights for today’s hvac system designerEngineers Newslettervolume 47–1A primer for non-electrical engineersHarmonic Distortion in Electrical SystemsThe quest to lower electrical energyconsumption of HVAC and otherelectrically-driven equipment has ledto the introduction of 'non-linear'electrical loads to the electrical grid.Harmonic distortion caused byincreasing non-linear loads can resultin issues in a building's electricalsystem.This newsletter provides a simplifiedexplanation of the causes of harmonicdistortion by taking the reader throughsome electrical system basics andmoving on to what harmonic distortionmeans and why it matters. It'sintended for those with little or noexperience with electrical systems.The term harmonics is used to describe adistortion in the fundamental voltage and/or current waveform supplied from a utilityor generator. In technical terms it's amathematical way to describe thedistortion. In a practical sense it gives usterminology to talk about the problems,both potential and real, due to theproliferation of energy saving devices.Voltage is determined at thetransformer serving the building. Manyvoltage choices are possible but oncefixed by the transformer the voltagedownstream of that transformer remainsrelatively constant. There are factorswhich will alter the average voltage butthese tend to be short term.Start with the basicsCurrent, or amperage, depends on thesupplied voltage and the electrical loadsin the building. For a given building, asthe electrical load increases so does thecurrent flow. A combination of current,voltage, and power factor are used todetermine the power used by thebuilding.Before we talk about the distortion let'sback up and look at what is beingdistorted. Distortion can happen in anyelectrical system regardless of how thepower is supplied to the system. For thisdiscussion we assume electrical power isbeing supplied to the building from thecommon electrical grid. Harmonics onsystems supplied by onsite generatorshave some unique problems as discussedin an earlier Engineers Newsletter, "HowVFDs Affect Genset Sizing", volume 35-1.Frequency is determined on a countryby-country basis. The United States, forexample, uses 60 Hz, other countriesmay use 50 Hz, but within a distributiongrid the utility supplying the power willstay with one frequency. This frequencyis called the fundamental frequency. Itis stable and consistent even whenvoltage or current change.Power is supplied to most buildings froman electrical utility. The utility providespower via an electrical distribution gridwith wires going to each building. The keycomponents of the supplied power are thevoltage, current, and frequency. 2018 Trane. All rights reserved.1
Figure 1 shows one cycle of afundamental 60 Hz waveform. It's calleda periodic waveform because of therepeating nature. The horizontal axis istime. As time passes the wave repeatsover and over in the same shape. Theshape can be mathematically describedas a sine wave.As shown in Figure 2 each completecycle of the wave represents 360degrees of rotation. Counting thenumber of complete wave cycles persecond yields the frequency of thewave. The Y axis is used to definemagnitude.Figure 1. One cycle of a 60 Hz periodic waveformtimeFigure 2. The number of complete wave cycles per second yields the frequency of the waveone wave cycleAlternating power, or AC power, meansthat the voltage supplied variesbetween positive and negative values asshown in Figure 3. This defines thefundamental voltage waveform suppliedto the building.The final piece for a basic understandingof power supply is the current signal.The utility defines the fundamentalfrequency and voltage but the currentsignal is dependent on the load. Therelationship between the voltagewaveform and the current waveform isdependent on the type of electrical load.This relationship is key to understandinghow harmonic currents are created.090180270360(0)90180270360(0)one wave cycleFigure 3. Positive and negative voltage variation in alternating powerpeak value 0time-peak valueFigure 4. Waveform difference between current and voltage magnitude (resistive load).Types of electrical loadsvLinear loads draw current evenly and inproportion to voltage throughout theduty cycle; the sinusoidal waveform ofthe incoming power remains intact.There are three types of linear loads.We'll start with resistive loads. Electricresistance heaters are a commonexample of a resistive load. For theseloads the waveforms for voltage andcurrent are different only in magnitudeas shown in Figure 4.Inductive loads, e.g., commonelectrical motors, result in a currentsignal that is shifted slightly (Figure 5)from the voltage signal. This shift iscalled lagging because for a given pointon the time scale, the current waveformpasses through that point after thevoltage waveform passes the samepoint.2Trane Engineers Newsletter volume 47-1ivitimeFigure 5. Current signal that is shifted slightly from the voltage signal (inductive load).vivitimeproviding insights for today’s HVAC system designer
A third type of linear load is capacitiveloads. A capacitive load shifts thecurrent signal to lead the voltage signal.There aren't many work-producing loadsthat have a capacitive character butcapacitors are sometimes added toelectrical systems to balance theinductive loads.When the voltage and currentwaveforms line up, as they do withresistive loads, the voltage multiplied bycurrent is always positive (Figure 6).However when the voltage and currentwaveforms are shifted, as withinductive loads, there are occasionswhen the product of voltage timescurrent is negative (Figure 7). Thenegative portion (caused as storedenergy is released) doesn't contributeto the positive work done by the load.The non-productive power is indicatedby the displacement power factor.Figure 6. Resistive loads always consume positive powerpower90º360ºvoltageFigure 7. Current and voltage waveforms shifted (inductive) consume positive and negative power.current lagging the voltage by 30ºpoweraveragepower90ºDisplacement power factor is defined asthe ratio of positive work actually done(true power) to the positive work thatwould have been done if the waveformsaligned.Although we’re discussing linearelectrical loads, the concept of currentflow that doesn't do positive work isimportant to understand.270ºcurrentAdding capacitors to systems withinductive loads improves thedisplacement power factor of thesystem by shifting the combinedwaveform toward unity.When voltage and current waveformsare not aligned some fraction of thecurrent isn't doing positive work. Theextra current must be generated by theutility and transmitted through theelectrical distribution system eventhough the current isn't doing positivework. Anytime current travels thoughthe electrical grid there are lossesassociated with the resistance of thesystem.180º180º270º360ºcurrentvoltageTo a "non-electrical" engineer thisconcept may not make sense. To betterunderstand, it's helpful to think ofinductors and capacitors as energystorage devices. They affect the currentby temporarily storing some of theenergy internally. An inductive load,such as a motor, inherently storesenergy as the voltage approaches thepositive or negative maximum. As thevoltage drops back toward zero, thestored energy is released back onto thegrid delayed in time.A capacitor works just the opposite. Byshifting the current value in time relativeto the voltage, these devices affect thecurrent flow without doing any actualwork. As stated earlier, even though theshifted current isn't doing any positiveproviding insights for today’s HVAC system designerwork, this current still needs to begenerated and transmitted by the utilitycompany.Non-linear loads distort the originalcurrent and voltage waveforms bydrawing current in instantaneous pulsesthat are disproportionate to voltage.Switch-mode power supplies (SMPS),found in computers, servers, monitors,printers, photocopiers, telecomsystems, broadcasting equipment, andvariable-speed motors and drives, areexamples of non-linear loads. Singlephase, non-linear loads are prevalent inoffice equipment, while three-phase,non-linear loads are widespread in largerelectrical systems.Trane Engineers Newsletter volume 47–1 3
Non-linear electric loads arecharacterized by a non-constantresistance during the applied voltagewaveform. Because the resistance is notconstant the resulting current waveformdoes not match the applied voltagewaveform. Each of the various non-linearloads have a unique resistancecharacteristic, and thus, a unique currentwaveform shape.The common SMPS load consists of a2-pulse (full wave) rectifier bridge (toconvert AC to DC) and a large filtercapacitor on its DC bus. This load drawscurrent in short, high-amplitude pulsesthat occur around the positive andnegative peaks of voltage. The resultingcurrent waveform is shown in Figure 8.Figure 9. Resultant waveform for the combination of fundamental and 3rd harmonicfundamental 60 hz waveformresultant waveform180 hz waveform (3rd harmonic)Harmonics. As mentioned earlier, thepresence of harmonics in electricalsystems means that current and voltageare distorted and deviate from sinusoidalwaveforms.Figure 8. Common SMPS current waveformTo demonstrate we’ll start with afundamental 60 Hz sine wave, similar tothe one shown in Figure 1, and add asecond sine wave with a frequency of 180Hz (or 3rd harmonic). Figure 9 shows the60 Hz wave in orange and the 180 Hzwave in gray. The waves are combined byadding the area under each curve.This power conversion createsharmonics. When the rectifier convertsincoming AC power to DC power, itsdemand for current rapidly cycles on andoff. This cyclic power draw distorts theoriginal shape of the current waveform,“chopping up” the sinusoidal shape andimposing new waveforms that aremultiples —harmonics — of the originalsignal. These harmonics are reflectedback onto the electrical system. 1 Thecombination of the fundamental sinewave and its multiples cause “harmonicdistortion,” a new waveform of anentirely different shape.Another way to look at this is that at anypoint along the x-axis, the value of theorange wave is added to the value of thegray wave. When both waves have the4Trane Engineers Newsletter volume 47-1The harmonic frequencies are alwaysinteger multiples of the fundamental.Figure 10 shows the resulting waveformwhen second, third and fourth harmonicsare added to the fundamental waveform.Figures 9 and 10 show a single harmonicbeing added to the fundamental waveformto illustrate how the addition of harmonicschanges the shape of the resultingwaveform. The waveform addition used inFigure 10 can be used to add multipleharmonic waveforms at the same time.Figure 10. Resulting waveforms for 2nd, 3rd and 4th harmonicsoutput waveform2nd harmonicθ2ffundamental3rd harmonicAlthough the circuit is supplied by a60 Hz sinusoidal voltage waveform, theresulting current waveform shown inFigure 8 isn't a simple 60 Hz sinusoidalwaveform. This waveform can bedescribed mathematically as being thecombination of many sine waves ofdifferent frequencies.To better understand this, it's necessaryto understand how sine waves areadded.same sign, e.g., both are positive, themagnitudes add. When the waves haveopposite signs the values subtract. Theresult is the dotted blue wave.θ3fharmonic4th harmonicθ4fharmonic waveformscomplex waveformsproviding insights for today’s HVAC system designer
It's necessary to use many harmonicwaves to produce the complicatedwaveforms created by non-linear loads.Figure 11 shows the addition of 3rdthrough 15th harmonics to create a"square" waveform.Figure 11. Resulting square waveform with the addition of the 3rd to 15th harmonicsfundamentalMore on power factor. The previoussection on linear electrical loadsexplained that the displacement powerfactor is used to indicate how muchnon-productive current is required bythe linear load. Similarily, non-linearloads also result in non-productivecurrents. These currents are quantifiedby distortion power factor.The total, or true, power factor for asystem is the combination ofdisplacement power factor anddistortion power factor. These nonproductive currents cost the utility.Although the utility can't charge for theextra current on a kW basis they mayinclude a charge (penalty) for a lowpower factor. For example, in somemarkets a low power factor of 80percent could be charged a 16%percent surcharge.2resultant ‘square’ waveodd harmonics(3rd to 15th)Displacement and Distortion Power Factor Comparison.Linear Loads, Displacement Power FactorNon-Linear Loads, Distortion Power Factor Linear loads do not change the shape of thecurrent waveform, but may change thephase angle between voltage and current. With a non-linear load, the current is drawnfrom the utility in pulses which may occurmultiple times per electrical cycle.If the power company includes a chargefor low power factor there is a directcost for harmonic distortion. Power factor correction for linear loads canbe achieved by adding capacitance to offsetthe inductive effect of the motors and realign current with voltage. Non-linear loads create harmonic currents athigher frequencies in addition to the originalcurrent frequency. Harmonic currents travel through theelectrical system along with thefundamental current. Electrical systemscan tolerate some harmonic contentbut when the harmonics are excessivea host of issues can arise. Problemscaused by harmonics can bewidespread throughout the system,e.g., overheating of distributionequipment, or localized to thedisruption of sensitive equipment, andinterference with telecommunicationcircuits, etc. Voltage distortion resultingfrom the current distortion, can alsoresult in equipment problems. In linear circuits, the sinusoidal currentsand voltages are of one frequency. Thedisplacement power factor arises only fromthe difference in phase between the currentand voltage.Power factor correction can be achieved usingfilters designed to pass only line frequency(50 or 60Hz), reducing harmonic current, andmaking the non-linear device now look like alinear load. Distortion power factor is a measure of howmuch the harmonic distortion of a loadcurrent decreases the efficiency of the powertransferred to the load.providing insights for today’s HVAC system designerTrane Engineers Newsletter volume 47–1 5
Quantifying harmoniccontentFigure 12. Harmonic content of typical 6-pulse variable-frequency drive10010090It's typical for the magnitude of theharmonics to decrease as the order ofthe harmonic increases. As a result,sometimes higher order harmonics areignored because their contribution to thetotal is limited.There are several metrics to helpdetermine and measure the distortioncaused by harmonics.Total harmonic distortion (THD) is ameasure of the effective value of theharmonic components of a distortedwaveform.3 It can be calculated for eithercurrent or voltage but is most often usedto describe voltage harmonic distortion.It’s mathematically calculated as the rootsum-square of harmonic components tothe fundamental component. THD canbe measured for an existing system orcalculated for a proposed system usingthe following equation:where:Mh individual harmonic componentM1 fundamental componentM can be either voltage or current6Trane Engineers Newsletter volume 47-180harmonic current (%)There are many different types of nonlinear electrical loads in operation today.Each type has a unique waveform anddistinct harmonic content. One way todescribe the harmonic content of aparticular source is to show themagnitude (as a percentage) andfrequency of the harmonic waves thatmake up the resultant wave. For exampleFigure 12 illustrates the most notableharmonics for a switch mode powersupply or 6-pulse, variable-frequencydrive. The missing harmonics are notshown because they are zero and do notcontribute to the distortion.7060504030202014910015786511131917order of harmonic componentHowever, even a small current can have ahigh THD which can be misleadingbecause it may not have significantimpact if operating in light load conditions(such as variable-speed drive). Asmentioned earlier, current distortionresults in voltage distortion. There is asimilar metric used for current called thetotal demand distortion (TDD).TDD offers better insight by providing“the total root-sum-square harmoniccurrent distortion, in percent of themaximum demand load current.” 4Knowing these equations is not requiredin most cases but it is important todistinguish between current distortionand voltage distortion.In practice the THD and harmoniccontent of the voltage and current in anelectrical system are measured by apower quality analyzer. The analyzermeasures the electrical system similar toa voltage meter and is able to display thedetailed harmonics content as well as thecalculated THD.How much is too much?When it comes to harmonics knowinghow much is too much can be difficult todetermine. Calculating THD and TDD fora proposed system is a complicatedprocess that requires a great deal ofinformation about the system and thenon-linear loads it will serve.442325While the list of potential problemsthat could result from harmonicdistortion is long, it should be notedthat in many cases harmonics in theelectrical system do not cause issues.The potential for problems is based on;the amount of harmonic distortionpresent, the size of the electricalsystem, and the sensitivity ofequipment within the system toharmonics.When non-linear loads are a smallfraction (less than 20 percent) of thetotal load, the potential to causeproblems is very low. However asmore and more non-linear loads areadded to the grid, the potential forharmonics-related issues increases.Think of harmonics as the ripplescaused by tossing pebbles in a pond.In a large pond, the ripples dissipateover distance and leave much of thewater undisturbed. In a small pond,the ripples reach the nearby shoresand reflect back, resulting in a chaos ofinteracting waves. Similarly, the size ofthe distribution system and the“stiffness” or “softness” of theelectrical system influence the degreeto which harmonics affect otherequipment. A large system with stiffpower not only reduces the voltagefluctuation that occurs when anelectrical load is added to the system,but it also reduces disruptive harmoniceffects.5providing insights for today’s HVAC system designer
Standard IEEE 519 is the mostcommonly referred to standard whendefining recommended limits forharmonic distortion. It’s primarilyintended to define limits for the amountof distortion that a building can placeback on the electrical grid. Distortionplaced back on the electrical grid by onecustomer can impact other customerson the same grid. The standard setsrecommended limits for harmonics atthe point of common coupling (PCC),i.e., the electrical connection betweenthe building and the electrical grid (seesidebar).What can be done tocontrol harmonics?From a building owner’s perspective itcan be difficult to predict the impact ofharmonics on the electrical componentsand equipment in the building. Allbuildings contain non-linear electricloads that are generating harmonicdistortion but few buildings suffer any illeffects. This doesn't mean harmonicscan be ignored because there arebuildings where they do createproblems.Caution is warranted when a largeamount of non-linear load is added to anexisting electrical system. This canhappen when "energy saving" upgradesare made that convert linear loads tonon-linear loads.A common approach to avoidingproblems caused by harmonics is tomitigate harmonics where they arecreated. It's not a practical option if thesource of the harmonic distortion is alarge quantity of small loads, e.g.,personal computers, but if the buildinghas large non-linear electric loads it maymake sense.There are many types of mitigationstrategies that can be applied at theequipment level with varying levels ofharmonic reduction and cost. Theamount of reduction required isdependent on the other non-linear loadson the system and the sensitivity ofother components and equipment toharmonic distortion. In short, it can bechallenging to determine how muchmitigation is needed.providing insights for today’s HVAC system designerStandard IEEE 519 recommended limits.Table 1. Current distortion limits for systems rated 120V through 69kV.short-circuit current Total demand distortion (TDD)load currentlimitlarge load on small systemsmall load on large system 205%20-508%50-10012%100-100015% 100020%more restrictive TDD limitless restrictive TDD limitTable 2. Voltage distortion limits.Bus votage V at PCCIndividual harmonic(%)Total harmonic distortion (THD)limitV 1.0 kV5.08%1kV V 69 kV3.05%69 kV V 161 kV1.52.5%161 kV V1.01.5%**High-voltage systems can have up to 2.0% THD where the cause is an HVDC terminal whose effects willhave attenuated at points in the network where future users may be connected.The IEEE 519 limits for the PCC aresometimes applied at the equipmentlevel. It's a stringent requirement toapply at the equipment level, and mayadd unnecessary cost, but it can beeasy to specify and can reduce theimpact a piece of equipment mighthave on the rest of the equipmentwithin the system.understanding potential issues anddetermining resolutions for harmonics inelectrical systems.By Dave Guckelberger, Bob Coleman andChris Hsieh, Trane. To subscribe or viewprevious issues of the Engineers Newsletter visittrane.com/EN. Send comments to ENL@trane.com.New electrical systems can bedesigned to manage some over-heatingissues caused by harmonic currents;oversized neutrals and de-ratedtransformers for example. Systems canalso be designed with transformers andother devices to reduce thetransmission of harmonics to otherequipment on the electrical system.ReferencesFinal thoughts[4] IEEE Std 519-2014 - "IEEE RecommendedPractice and Requirements for Harmonic Controlin Electric Power Systems. "Harmonic distortion on electricalsystems increases with the increasedpercentage of non-linear loads. Thedistortion doesn't always causeproblems but it certainly can. Asproblems with harmonic distortionincrease with the acceleration ofenergy-saving devices so do thesolutions for reducing harmoniccontent. Understanding the source ofharmonic distortion provides a basis for[1] IEEE 519-2014 defines acceptable limits forharmonics in electrical power systems. For moreinformation, visit http://standards.ieee.org.[2] BC Hydro website. rgy-use/electricityrates/power-factor.html[3] “Electrical Power Systems Quality” by Dugan,McGranaghan, Santoso, and Beaty (ISBN 0-07138622-X).[5] Nebuda, C. and B. Bradley. "How VFDs AffectGenset Sizing." Engineers Newsletter vol. 35-1.2006.Trane Engineers Newsletter volume 47–1 7
Join your local Trane office for the 2018 Engineers Newsletter LIVE!Mark your calendar!Chilled-Water System Decisions. Many chilled-water system decisions are madeduring the course of the design process. Those decisions lead to other applicationspecific system decisions – such as bypass line sizing and length, pump location, icetank versus chiller location, use of pressure independent valves, buffer tank size,control of chillers in series etc. This ENL covers the reasons for many system designdecisions.(March)Controls Communication Technologies. Recent innovations in the industry havemade open, standard communication protocols that deliver flexible, interoperablecontrol systems more prevalent today. This ENL will review various communicationprotocols (using both wired and wireless technologies), discuss where each bestapplies, and describe ways to ensure the expectations of the owner are met. (May)Demand-Controlled Ventilation. The mobility of a building’s occupants poses aventilation challenge: To bring enough outdoor air into the building to help ensuregood indoor air quality without wasting energy by bringing in (and conditioning) toomuch. This ENL will discuss various methods used to vary outdoor airflow based onactual demand. It also reviews the related requirements for compliance withASHRAE Standards 62.1 and 90.1. (November)Contact your local Trane office for dates and details.Earn PDH credit - no charge and on-demand!NEW Online Courses Available!View all courses at www.trane.com/ContinuingEducationHigh-Performance Air Systems examines the properties of high-performance airsystems and provides guidance on their design. Topics include right-sizing andproper component selection, duct design guidelines, system control strategies,selection for part-load efficiency and much more.Demand Response in Commercial Buildings discusses the relevantimprovements that load shifting and demand response can provide, with examplesof the types of utility and funding programs that are available.Trane and the Circle Logo are trademarks of Trane in the United States and other countries. IEEE is a registered trademarkof The Institute of Electrical and Electronics Engineers, Inc. All trademarks referenced are the trademarks of theirrespective owners.Trane,A business of Ingersoll RandFor more information, contact your local Traneoffice or e-mail us at comfort@trane.com8Trane Engineers Newsletter volume 47–1This newsletter is for informational purposes only and does not constitute legal advice.Trane believes the facts and suggestions presented here to be accurate. However, final design andapplication decisions are your responsibility. Trane disclaims any responsibility for actions taken onthe material presented.ADM-APN065-EN (March 2018)
Harmonic Distortion in Electrical Systems The quest to lower electrical energy consumption of HVAC and other electrically-driven equipment has led to the introduction of 'non-linear' electrical loads to the electrical grid. Harmonic distortion caused by increasing non-linear loads can result in issues in a building's electrical system.
IEEE 519-2014 Target - 5%. IEEE 519-2014 Current distortion level of for systems 120V –69kV Standards - IEEE. Harmonic distortion - evaluation of harmonics TDD Total Demand Distortion of the current (used in e.g. IEEE-519:2014) Equal to THDi
Hammond Power Solutions Inc. ata subect to change without notice. MINIMIZE HARMONIC DISTORTION Non-linear current waveforms contain harmonic distortion. By using a HPS line reactor you can limit the inrush current to the rectifier in your drive. The peak current is reduced, the waveform is rounded and harmonic distortion is minimized.
Simple Harmonic Motion The motion of a vibrating mass-spring system is an example of simple harmonic motion. Simple harmonic motion describes any periodic motion that is the result of a restoring force that is proportional to displacement. Because simple harmonic motion involves a restoring force, every simple harmonic motion is a back-
b) Partial Weighted Harmonic Distortion (PWHD) c) Percentage individual harmonics I2, I3, I4, I5, , I13 Where: In is the average current harmonic, n, over the duration of the test from the spreadsheet. I1 is the average fundamental (1st harmonic) current over the duration of the test from the spreadsheet. 4. Compare the results with the tables in the next section.
Lesson 14: Simple harmonic motion, Waves (Sections 10.6-11.9) Lesson 14, page 1 Circular Motion and Simple Harmonic Motion The projection of uniform circular motion along any axis (the x-axis here) is the same as simple harmonic motion. We use our understanding of uniform circular motion to arrive at the equations of simple harmonic motion.
Chapter 11: Harmonic Motion 170 Learning Goals In this chapter, you will: DLearn about harmonic motion and how it is fundamental to understanding natural processes. DUse harmonic motion to keep accurate time using a pendulum. DLearn how to interpret and make graphs of harmonic motion. DConstruct simple oscillators.
Harmonic Patters The R G E M System* * * Harmonic Sell Signal Swing Sell Signal 100 pips profit We constantly keep an eye out for harmonic patters including the Bat, Butterfly, Crab, Gartley and Shark. While we use harmonic patterns for a variety of aspects in our trading, one of the mo
Asset management in Europe is mainly concentrated in six countries where almost 85% of the asset management activity takes place. The United Kingdom is the largest European asset management market, followed by France, Germany, Switzerland and Italy. Thepresence of large financial centres can explain the market concentration in these countries. The
