harmonics what are they

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Harmonics-what arethey. how tomeasurethem andhow to solvethe problem(in connection with Standards IEEE 1159- 1995& IEEE 519- 1992).AVISHAI RASH BScEE& PE Consulting EngineerY ericho 1Phone& Fax :03-6043807 Celular :050-349030E-mail : a [email protected] 61392It is common these days to hear or to readaboutHarmonics. In fact if we use thisexpression alone without any additionalterm or without any connection to aphysical value it has no electricalmeaning.0 What are Harmonics ? ( Basic terms )To express a deviation from a pure sinewave usually the term Harmonicscomponents is used .Together with theuse of the term Harmonics we mentionthe name of the famous mathematicianFourier who developed a mathematicalway to investigate a complex wave and toexpress it in a form that is simple anduseful.

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+ - T 4

A Deriodic function f(t)=f(t+T)This function (asit is periodic) canbedescribedas a Fourier series .f ( t )=-ao +alcosmOt+a2cos2mot+....+h, in2

1 m2 n=or f ( t )=-ao +C(a,cosnuOt+bnsinnw,t)Or inits trigonometric formm

n=lf ( r ) =c,+zc,, os(n~~ote,,)In Electricity Harmonics are described asHarmonics are sinusoidal voltages orcurrents having frequencies that areinteger multiples of the frequency atwhich the supply system is designed tooperate.The multiples are integer multiples 1-2-3-4-5 of the basic (fundamental) frequency50Hz . Accordmg to that we are dealing

fOllO\vS (REF IEEE 1159-1995) :

with frequencies of 50-100-150-200-250....2500Hz... that are added to thefundamental on a steady state base ,asopposed to instantaneous disturbings(dropout, dip, sag, notch, swell, etc..)Harmonics exist in power systems and areknown for years ,sowhy should we careabout them today ?The main reasons are :-Harmonics are harming many consumersin the power supply networks .-A ccorbg to new standards tcday the levelof harmonics in the supply network islimited.-Due to harmonics existence availablepower is reduced .These are the main reasons why thesedays we hear more about harmonics andother kind of disturbances in the powersupply network .Together with the growthin awareness to harmonics twophenomena arose :-M any people began to deal withharmonics.-M any new terms were added to theexisting technical vocabulary , some ofthem not clearly defined anywhere .Here I am going to state fromIEEE 5 19-1992 seven definitions that , nmy opinion , are very important andmisused in many places :One of the mostly used term inharmonics is THD or Total HarmonicDistortion (U & I ).

1- Total harmonic distortion disturbance&.The level of agiven electromagneticdisturbance caused by superposition ofthe emissionof all pieces of equipment ina given system .The ratio of the harmoniccontent to the rms value of the

0-7803-3330-6/96/$5.00 1996-IEEE83


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fimdamental quantity , expressed as apercent of the fundamental .2-Distortion factor (harmonic factor) .The ratio of the root-mean-square of theharmonic content to the root-mean-squarevalue of the fUndamental quantity ,expressed as a percent3- Harmonic factor . The ratio of theroot-sum-square (rss) value of all theharmonics to the root-mean-square valueof the fundamental .h n i c actor (for voltage) =!GGT

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harmonic factor (forcurrent) = 11

4- 1.T twoduct . The inductive influenceexpressed in terms of the product of itsroot-mean-square magnitude (I ) , inamperes , imes its telephone influencefactor (TI F).5- kV .T twoduct . Inductive influenceexpressed in terms of the product of theproduct of its root-mcan-squarcV t u d e , in kilovolts , times itstelephone influence factor (TIF).6- Telephone influence factor (TIF). For avoltage or current wave in an electricalsupply circuit ~ the ratio of the square rootof the sum of the squares of the weightedroot-mean-square values of all the sine-wave components (includmg alternatingcurrent waves both fundamental andharmonic) to the root-mean-square value(unweighted) of the entire wave .7- Total demand distortion (TDD). Thetotal root-sum-square harmonic currentdistortion , n percent of the maximumdemand load current (15 or 30 mindemand ).Remark : many of these definitions arebascd on or includc thc cxprcssion rmsthat is defined as root-mean-square(effective value) that has been found to beproblematic in systems where harmonicsare present .

h=WhereM h is the rms vnlue of hnrmonuiccomponent h of the quantity M.As a result of the use of ambiguousterms , the IEEE standards 1159-1995

and 5 19- 1992 begins with chaptersconcerning terms to use or morespecifically ambiguous terms to avoid .The terms described above have beentaken from these Standards . TheseStandards also point to the fact thatharmonics have been found guilty ofmany problems not only the classical onesdescribed in many books like Destructionof Power factor capacitors , Heating ofHV transformers harms to electronicdevices but also Flickering of lightingsystems , decrease in reliability ofcommunication systems , increase ininterferences to communication systems ,lost of balance in balanced systems , aiseof current and overheating in the 0conductor , overheating of switchboardsand more ....8 Whoare the vroducers of Harmonics ?In fact every electric power consumerwhose consumption behavior is not linearis an Harmonic producer . The importantpoint is to read carefully the informationabout the consumer and the electricnetwork data thus enabling to quantizeproperly the level of the harmonicpotential of each consumer so that itwont be minimized or ignored .The main Harmonics potential producersare :- Power supplies (linear and switchers)- UP S- Static Electronic motor soft starters- Static Variable speed dnvers

(VFD& VSD)- Large engines heavily loaded- Unloaded transformers- Overloaded transformers etc..OHOWdo we monitor Harmonics andintemret these results ?Monitoring equipment became lessexpensive during the last few years sothatmany people bought it and began tomonitor harmonics . As a resultdifferent techmques were used formonitoring and the reliability of theresults were not evident . As a directresult many interpretations were based onincorrect data and lead to wrong solutionsIn order to avoid this kmd of problemsIEEE wrote the 1 159-1995 standard :IEEE Recommended Practices forMonitoring Electric Power Quality .The first step in building an harmonicmonitoring plan is in describing its goal :

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Are we dealing with a site that has some.kind of problems suspected to beharmonics , or do we want to anticipatedisturbances in the power system ? Arewe dealing with low voltage or highvoltage problems ? Are we supposed tosolve a specific problem diagnosed asharmonics problem ? etc...

network as accurately as possible. llusmodel is the one that will enable us tointerpret the results and design a solutionto the problems found .The aspect and the impact of problemsconnected to harmonics are covered byE E E 519- 1992 :"IEEE RecommendedPractices and Requirements for Harmonic

overall assesmentof power quality

equipment problem

1 Suwested monitoring locations on a twical low voltage system(Based on IEEE 1159 -1995 D 39 figure 15 )

As it may be seen in the figure above for Control in Electrical Power Systems".each kind of monitoring it is necessary to Most of the time a proper monitoringfind the proper location and define the requires at least 24 consecutive recordingadequate parameters according to the hours of all the network parameters .predefined goal . The results of the monitoring areThi s god will then be the base upon computed according to the parameterswhich we design steps and locations used to define how ,where, nd how longwhere to install the measunng equipment, to record the data accordmg to pne of theand durations : Thl s is done according to models used for designing suitablethe description of the power dimbution solutions for the specific site .in the facility and what we thmk the flow It is crucial to understand that the modelof the harmonics path , hat is not defined is used to check the suitability of anyby the electric scheme of the network ,but solution to the site and not to derive a& y the dynamic impedance behavior solution from a model without a properof each consumer for each different on site check . A mistake of that landfrequency or harmonic .The electrical could lead to disastrous .results as far asbehavior or the flowing flux of the having a high voltage transformer blownharmonics in a network is changmg up.according to the consumers switchrig 8 WhataretheDossiblesolutions?ON&OFF who are harmonics generators It ishighly r i s k y to tak about the possibleor harmonics "pumps '' and their solution, as there is no automatic solutionresonance behavior in the network . A for harmonics, s stated above . Just thestable behavior that is representing the same it is possible to list the knownsystem usually it is quite complex to find exisnng solutions to harmonic problemsas we have consumers switching as l ong as it is reminded that it has to beON&OFF .That is why we have to find a based upon proper monitoring prior tomodel that wdl represent the speclfic solutiondesign.

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One of the most popular solutions( mostly the cheapest ) is to design theproper Band Reject Filter together withthe Power Factor Correction Capacitors .This way it is possible to achieve twogoals in one solution : Power FactorCorrection and Harmonic Reduction orControl . his solution is not deauate toall uroblems !In some cases , it is necessary to installBand Pass Filters for specific Harmonics.Thissolution is less popular, especiallyas it isquite expensive.Acwrdmgto spec& problems, here aresome special solutions like :A. Special transformers :- Delta Wye Delta- Delta Wye Wye- Wye Wye ( Coupled ,Common 0 ,Common or Isolated ground etc.. )- Wye G-Delta- Equal Homopolar 2% Impedance-ZigzagConnected Secondary- Magnetx Flux CompensationB. Harmonic InjectionC. DC hpple Injection

0 ConclusionIEEE 1159-1995 describes its purpose inthis matter : - The purpose of thisrecommended practice isto direct users inthe proper monitoring and datainterpretation of electromagneticphenomena that cause power qualityproblems . It defines power qualityphenomena in order to facilitatecommunication within the power qualitycommunity . T h ~ sdocument (REF :IEEE1159-1995) also forms theconsensus opinion about safe andacceptable methods for monitoringelectnc power systems and interpretingthe results . It further offers a tutorial onpower system disturbances and theircommon causes.The major problem with harmonics todayis that most of the Power Engineers areused to consider only the fundamental intheir power supplymg . Therefore PowerEnpeers are f aced with diuphenomena , especially unfarmliar to thecustomers who are suffering fromproblems in their locations .Nowadays quality is associate witheverythmg where we can measure it and- standards are leading us on the properway to arrive to l u s quality , hi s includes

harmonic monitoring engineering ofharmonic solutions and design of newelectncal plans .Although , harmonic can cause a lot ofproblems in sites where they exist in highlevels , proper monitoring and goodengineering can solve the problems atreasonablec o s t , and permit efficient useof power .

0BibliomphvRecommended Practices andRequirements for Harmonic Control inElectrical Power Systems RecommendedPracti ces for MonitoringElectric Power Quality .IEC-555-2 (First Edition 1982) :Disturbances in supply systems caused byhousehold appliances and similarelectrical aquipment .Power Systems HarmonicsJ .Amiaga,editionsJohnWiley& Sons .Electrical Power Svstems Oualitv HomeU: ttp://vmwelectrotek. om/pqbook/

IEEE 5 19- 1992 staadard :IEEE

E E E 1159-1995 standard 1 IEEE

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harmonics what are they

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