Harmonics are enerated in the sy stem Gener all y the effect of harmonics is studied in olta e or current The current harmonics flow in the sy stem enerates olta e harmonics whic h resul ts into pow er harmonics Pow er harmonics are than measured by ID: 24701 Download Pdf

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Harmonics are enerated in the sy stem Gener all y the effect of harmonics is studied in olta e or current The current harmonics flow in the sy stem enerates olta e harmonics whic h resul ts into pow er harmonics Pow er harmonics are than measured by

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ynops is The issue of harmonics is de bated at various lev els. Harmonics are enerated in the sy stem. Gener all y the effect of harmonics is studied in olta e or current. The current harmonics flow in the sy stem enerates olta e harmonics whic h resul ts into pow er harmonics. Pow er harmonics are than measured by ener gy meters . The flow of pow er harmonics and it effect on the ener gy measurement is discussed in this paper . Thou gh current harmonics are hi gh, pow er harmonics are ery small and contribution to ener gy is insi gnificant . The pow er harmonics direction is

opposite to fundamental pow er flow at the sourc e of harmonics so total pow er measured is less than fundamental pow er . The linear loads consumes harmonics pow er from the sy stem. rmonics in pow er s st em a nd met ering How the har monics ar e gener ated Harmonics are enerated by an y load, whic h dra ws current not proportional to the olta e applied. Most loads are somew hat nonlinear , but some enerate more and hi gher lev el harmonics than others. These incl ude the following and man y more types of loads Static pow er con erters using th yristor or SCRs to contr ol the dri es Arc

furnaces , Arc elding sets and ov ens Ballast in hi gh pow er dischar e, mercury va por lamps, hi gh- pressur e sodium va por lamps and metal Halide li ghtin g etc. Swit chin g or phase contr olled C to DC pow er supplies, battery char ers and UPS for comput ers and comput er contr olled machines ransformer s operating near saturation Solid state frequenc y con erters for induction heating and cy clo con erters Induction furnaces and electrol ysis plants Har monic curr en , volta ge and pow er The sinusoidal olta es or fundamental val ue of olta e is defined by the equation ' E=Em Sin wt '

I=Im Sin wt Em and Im are the peak val ues. The RM S val ues and peak val ues has a ratio of 70 et the comple x olta e wa eform be repr esented by the equation 'E = E1m Sin wt+E2m Sin 2wt + E3m Sin 3wt + E4m Sin 4wt +…+ Enm Sin wt is applied to a circuit. et the equation of the resul tant current wa e be 'I= I1m Sin (wt+ 1) +E2m Sin (2wt+ 2) + E3m Sin 3wt+ 3) + E4m Sin 4wt+ 4) +…+ Enm Sin(n wt+n) The instantaneous val ue of the pow er in the circuit is p=ei watt or obtainin g the val ues of this prod uct , e will multipl y ev ery term of the olta e wa e, in turn, by ev ery term in the current

wa e. The erag e pow er supplied d uring a c cle w ould be equal t o the sum of the a erag e v alues ov er one cy cle of each indi vidual prod uct term. Henc e total pow er supplied by a comple x wa e is the sum of the erag e pow er supplied by each harmonic component acting independentl otal pow er is P= E1I1cos1 + E2I2 Cos 2 + E3I3 Cos 3 + ……EnIn Cosn The first component is the fundamental pow er and other components are harmonic components . Henc e the total pow er is a sum of fundamental pow er and harmonic pow er . The direction of flow of indi vidual component should be consider ed appr

opriatel . A comple x wa eform consistin g offundamental and third harmonics is shown in the fi ure below by Surendr a J halora Pag e 1 of 3 In tr oduction A ell desi gned pow er plant enerates sinusoidal alt ernating current electrical pow er , thus a utility deli ers sinusoidal pow er or fundamental pow er to co s. co re nonlinear in nature and ca use distortion in the wa e shape and enerate other components at frequencies that are inte gral multiples of the fundamental frequenc . The combined wa e shape of all the frequencies is not a sinusoidal wa e shape and mak e an irre ular shape but

of repetiti e nature. The repetiti e deviation of either the olta e or current wa eform from a pure sinusoid is ly re re to combined wa e shape is a comple x wa e shape and can be decomposed by ourier transform method. The dist ortion components can be submul tiples of the fundamental frequencies in a pow er sy stem and ca use distortion in the sinusoidal wa e shape and are called harmonic distortion but enerally the inte er multiples are referr ed as harmonic components and are harmonic distortion. The harmonic components ma y be different in current and olta e wa eforms.

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Har

monics in thr ee phas e ys tem prod uced in the same wa y as in the sing le -phase sy stems . In the three phase sy stems following need to be consider ed All the third harmonics are equal in all phases of the circuit and they are in time phase. All harmonics, whic h are not multiples of three, ha e a phase displacement of 120 degr ee so that they can be dealt in the usual manner th th The , 11th and 17 harmonics ha e a neg ati e phase sequence of , , and B. th th th The , and harmonics ha e a positi e phase rotation of , , and B. re s, prod uction of harmonics will be affected by the

construction employ ed. When primary is connect ed in delta, in each phase the third harmonics current will be in phase and so prod uce circulatin g current round the mesh with the resul t that there will be no third harmonic current in the line current. When the primary is connect ed in 4wire star , the third harmonic current will flow throu gh line and return throu gh neutral wire. And in case of 3 wire star connection, third harmonics current is not returnin g there fore the line olta es will contain third harmonic components The fundamental pow er is enerated by the enerator and

transmitted to the load via Zs and l. the harmonic current ca uses distortion in the olta e at the points A and B. The distortion in the olta e will depend on the impedances . And the magnitude of harmonics currents . The nonlinear load dra ws a current with a comple x wa eform. The comple x current wa e shape will ca use drop across the l and Zs. Consider the Zs and l as linear impedances , the drop will be same as comple x current wa e shape. The olta e at point B is g minus the comple x olta e drop across the tw o impedances . Thus the harmonic pow er has neg ati e si gn as compar ed to the

fundamental pow er The total pow er is the sum of fundamental pow er and harmonic pow er thus the total pow er measured by the meter M2 is fundamental pow er consumed minus the harmonic pow er enerated. The harmonic pow er is flowing from the load to the utility and meters will measure less total pow er The comple x current wa eform will distort the olta e at the point A but the magnitude of distortion will be less as compar ed to the point B. The linear load will dra w current proportional to the olta e. Thus it will dra w some comple x current due to the drop in the olta e due to comple x

current wa eform. The comple x current is in phase with the olta e applied thus the total pow er measured by the meter M1 is the fundamental pow er consumed by the load plus complex or harmonic pow er fed due to olta e at the point B. Thus the harmonic ener gy is flowing from the utility to the consumer and the pow er meter ed is more than the pow er actuall y consumed in the load. ets consider a simple mathematics to illustrate the abov e. 50% third harmonic current is enerated by a load ca uses 10% drop in the olta e. The harmonic pow er is 10*50/ 100=5%. Thus otal pow er will be 95% of the

fundamental pow er actuall y consumed in the nonlinear load. Thus a otal pow er meter will measure 5% less than a undamental pow er meter . The 10% drop will ca use 10% harmonic current to flow in the linear load thus total pow er is 10*10/ 100=1 %. Thus a total pow er will measure % more pow er than a fundamental pow er meter Some experiments ha e been cond ucted t o prov e the explanation and the resul ts is shown in the table below eter ing an d flow of har monics The Diagram of meterin g point and load is shown below Zs Zl Vg Met er M Line ar lo ad Met er M2 Non linea r connections can be

used to understand the flow of harmonic pow er in the sy stem due to nonlinear loads. ge to wh enerates fundamental pow er . The Zs is the sourc e impedance and l is the distribution netw ork impedance, whic h a load see from the load end. The l ca uses drop in the olta e due to load current. Meter M2 measures pow er dra wn by the nonlinear load. The olta e distortion at the point mark ed A and B depends on the impedances Zs and l. The linear load is connect ed in the sy stem and pow er dra wn by the linear load is measured by meter M1. The fundamental val ues are consider ed as 100% and other

harmonic components are present ed corr esponding to fundamental val ues. The table below shows flow of harmonics corr esponding to harmonics in olta e and current harmonics abov e. these resul ts are tak en by simulating the loads and hi gh line impedances to enlar e the effect of harmonics. Pag e 2 of 3

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3P3W and 3P4W me as ur emen The harmonics appear differentl y in the wa y the connections are done. 3phase 4 wire connect ed meter will measure the olta es phase to neutral and 3p3w meter measure the phase olta es thus both the meter will perc ei e different harmonics under

the same harmonics flow in the sy stem. The harmonics measurement is different in different type of connection as illustrated abov e in three phase sy stems . Thus the total pow er measured will also be different for the same harmonics in the sy stem. Pag e 3 of 3 onclus ion t is evident form the test resul ts and stud y done by various engineers across the orld that the harmonics are enerated by non linear loads. The enerated harmonics flows back to the au transformer s and capacit ors. The resonanc e due to harmonics is quit e c ommon w hich leads to ex cessi e RM S current and more loading

than actual useful pow er transferred or deli ered. The total pow er measurement is alw ys less than the fundamental pow er measurement. The consumer enerating harmonics is meter ed less if total pow er is meter ed and consumers who are not enerating the harmonics are absorbin g harmonics and meter ed more than what is electrical sy stem and penalizes innocent and fair consumers The non-linear consumers are increasin g and are more than the linear consumers . The loss of reven ch re du to eneration than the gain in re enue due to harmonics pow er consumed when the total pow er is measured.

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