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Harmonics What Are They.Pdf Harmonics - what are they. how to measure them and how to solve the problem (in connection with Standards IEEE 1 159- 1995 & IEEE 5 19- 1992 ). AVISHAI RASH BScEE&PE Consulting Engineer Yericho 1 P.O.Box 39292 Tel-Aviv 61392 Phone & Fax : 03-6043807 Celular : 050-349030 E-mail : a [email protected] It is common these days to hear or to read with frequencies of 50-100-150-200-250 about “Harmonics” . In fact if we use this ....2500Hz ... that are added to the expression alone without any additional fundamental on a steady state base , as term or without any connection to a opposed to instantaneous disturbings physical value it has no electrical (dropout, dip, sag, notch, swell, etc..) meaning. Harmonics exist in power systems and are 0 What are Harmonics ? ( Basic terms ) known for years , so why should we care To express a deviation from a pure sine about them today ? wave usually the term Harmonics The main reasons are : components is used .Together with the -Harmonics are harming many consumers use of the term “Harmonics” we mention in the power supply networks . the name of the famous mathematician -Accorbg to new standards tcday the level Fourier who developed a mathematical of harmonics in the supply network is way to investigate a complex wave and to limited. express it in a form that is simple and -Due to harmonics existence available useful. power is reduced . These are the main reasons why these T” days we hear more about harmonics and other kind of disturbances in the power supply network .Together with the growth in awareness to harmonics two phenomena arose : -Many people began to deal with harmonics. +-T4 -Many new terms were added to the existing technical vocabulary , some of them not clearly defined anywhere . Here I am going to state from A Deriodic function f(t)=f(t+T) IEEE 5 19-1992 seven definitions that , in This function (as it is periodic) can be my opinion , are very important and described as a Fourier series . misused in many places : 1 f(t)= -ao +alcosmOt+a2cos2mot+....+h, sin One of the mostly used term in 2 harmonics is THD or Total Harmonic Distortion (U & I ). 1m or f(t)= -ao + C(a,cosnuOt +bn sinnw,t) 2 n=l Or in its trigonometric form m f(r) = c, + zc,,cos(n~~ot - e,,) n=l In Electricity Harmonics are described as fOllO\vS (REF IEEE 1 159-1995) : “Harmonics are sinusoidal voltages or currents having frequencies that are integer multiples of the frequency at 1- Total harmonic distortion disturbance which the supply system is designed to &.The level of a given electromagnetic operate “. disturbance caused by superposition of The multiples are integer multiples 1-2-3- the emission of all pieces of equipment in 4-5 of the basic (fundamental) frequency a given system . The ratio of the harmonic 50Hz . Accordmg to that we are dealing content to the rms value of the 0-7803-3330-6/96/$5.00 1996-IEEE 83 fimdamental quantity , expressed as a and 5 19- 1992 begins with chapters percent of the fundamental . concerning terms to use or more 2-Distortion factor (harmonic factor) . specifically ambiguous terms to avoid . The ratio of the root-mean-square of the The terms described above have been harmonic content to the root-mean-square taken from these Standards . These value of the fUndamental quantity , Standards also point to the fact that expressed as a percent harmonics have been found guilty of 3- Harmonic factor . The ratio of the many problems not only the classical ones root-sum-square (rss) value of all the described in many books like Destruction harmonics to the root-mean-square value of Power factor capacitors , Heating of of the fundamental . HV transformers harms to electronic devices but also Flickering of lighting hnicfactor (for voltage) = !GGT systems , decrease in reliability of EI communication systems , increase in interferences to communication systems , lost of balance in balanced systems , raise harmonic factor (for current) = 11 of current and overheating in the “0” conductor , overheating of switchboards and more .... 4- 1.T twoduct . The inductive influence 8 Who are the vroducers of Harmonics ? expressed in terms of the product of its In fact every electric power consumer root-mean-square magnitude (I) , in whose consumption behavior is not linear amperes , times its telephone influence is an Harmonic producer . The important factor (TIF). point is to read carefully the information 5- kV.T twoduct . Inductive influence about the consumer and the electric expressed in terms of the product of the network data thus enabling to quantize product of its root-mcan-squarc properly the level of the harmonic Vtude , in kilovolts , times its potential of each consumer so that it telephone influence factor (TIF). won’t be minimized or ignored . 6- Telephone influence factor (TIF). For a The main Harmonics potential producers voltage or current wave in an electrical are : supply circuit ~ the ratio of the square root - Power supplies (linear and switchers) of the sum of the squares of the weighted - UPS root-mean-square values of all the sine- - Static Electronic motor soft starters wave components (includmg alternating - Static Variable speed dnvers current waves both fundamental and (VFD& VSD) harmonic) to the root-mean-square value - Large engines heavily loaded (unweighted) of the entire wave . - Unloaded transformers 7- Total demand distortion (TDD). The - Overloaded transformers etc.. total root-sum-square harmonic current OHOW do we monitor Harmonics and distortion , in percent of the maximum intemret these results ? demand load current (15 or 30 min Monitoring equipment became less demand ). expensive during the last few years so that Remark : many of these definitions are many people bought it and began to bascd on or includc thc cxprcssion ”rms” “monitor” harmonics . As a result that is defined as root-mean-square different techmques were used for (effective value) that has been found to be monitoring and the reliability of the problematic in systems where harmonics results were not evident . As a direct are present . result many interpretations were based on incorrect data and lead to wrong solutions In order to avoid this kmd of problems h=l IEEE wrote the 1 159-1995 standard :” Where Mh is the rms vnlue of hnrmonuic IEEE Recommended Practices for component h of the quantity M. Monitoring Electric Power Quality “. As a result of the use of “ambiguous” The first step in building an harmonic terms , the IEEE standards 1159-1995 monitoring plan is in describing its goal : 84 Are we dealing with a site that has some network as accurately as possible. llus .kind of problems suspected to be model is the one that will enable us to harmonics , or do we want to anticipate interpret the results and design a solution disturbances in the power system ? Are to the problems found . we dealing with low voltage or high The aspect and the impact of problems voltage problems ? Are we supposed to connected to harmonics are covered by solve a specific problem diagnosed as EEE 5 19- 1992 :"IEEE Recommended harmonics problem ? etc... Practices and Requirements for Harmonic overall assesment of 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 monitoring find the proper location and define the requires at least 24 consecutive recording adequate parameters according to the hours of all the network parameters . predefined goal . The results of the monitoring are This god will then be the base upon computed according to the parameters which we design steps and locations used to define how , where , and how long where to install the measunng equipment , to record the data accordmg to pne of the and durations : Thls is done according to models used for designing suitable the 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 model of the harmonics path , that is not defined is used to check the suitability of any by the electric scheme of the network , but solution to the site and not to derive a & by the dynamic impedance behavior solution from a model without a proper of each consumer for each different on site check . A mistake of that land frequency or harmonic .The electrical could lead to disastrous .results as far as behavior or the flowing flux of the having a high voltage transformer blown harmonics in a network is changmg up. according to the consumers switchrig 8 WhataretheDossiblesolutions? ON&OFF who are harmonics generators It is highly risky to talk about the possible or harmonics "pumps '' and their solution, as there is no automatic solution resonance behavior in the network . A for harmonics , as stated above . Just the stable behavior that is representing the same it is possible to list the known system usually it is quite complex to find exisnng solutions to harmonic problems as we have consumers switching as long as it is reminded that it has to be ON&OFF . That is why we have to find a based upon proper monitoring prior to model that wdl represent the speclfic solutiondesign. 'I 85 One of the most popular solutions harmonic monitoring engineering of ( mostly the cheapest ) is to design the harmonic solutions and design of new proper Band Reject Filter together with electncal plans .
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