electrical power quality of iron and steel industry in turkey

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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 46, NO. 1, JANUARY/FEBRUARY 2010 1

Electrical Power Quality of Ironand Steel Industry in Turkey

Özgül Salor, Member, IEEE , Burhan Gültekin, Student Member, IEEE , Serkan Buhan, Burak Boyrazoglu,

Tolga˙Inan, Tevhid Atalık, Adnan Açık, Alper Terciyanlı, Student Member, IEEE ,Özgür Ünsar, Student Member, IEEE , Erinç Altıntas, Yener Akkaya, Ercüment Özdemirci,

Isık Çadırcı, Member, IEEE , and Muammer Ermis, Member, IEEE

Abstract—The iron and steel industry has been growing increas-ingly in Turkey in the last decade. Today, its electricity demand isnearly one tenth of the installed generation capability of 40 GW inthe country. In this paper, power quality (PQ) investigations basedon the arc furnace installations of the iron and steel plants usingfield measurements according to the international standard IEC61000-4-30 are documented. Interharmonics and voltage flickerproblems occurring both at the common-coupling points of thoseplants and at the arc furnace and static var compensator (SVC)systems of the plants themselves are determined with the useof GPS receiver synchronization modules attached to the mobilePQ measurement systems. It has been observed that flicker andinterharmonic problems are dominant at the points of common

Paper PID-2009-04, presented at the 2007 Industry Applications SocietyAnnual Meeting, New Orleans, LA, September 23–27, and approved forpublication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS bythe Metals Industry Committee of the IEEE Industry Applications Society.Manuscript submitted for review November 30, 2007 and released for publi-cation June 22, 2009. This work was supported by the Public Research GrantCommittee (KAMAG) of The Scientific and Technological Research Councilof Turkey (TÜBITAK).

Ö. Salor and A. Açık are with the Power Electronics Department,

TÜB˙ITAK UZAY Research Institute, The Scientific and Technological Re-search Council of Turkey (TÜBITAK), 06531 Ankara, Turkey (e-mail: ozgul.

[email protected]; [email protected]).B. Gültekin, T. Inan, and A. Terciyanlı are with the Middle East Techni-

cal University, 06531 Ankara, Turkey, and also with the Power ElectronicsDepartment, TÜBITAK UZAY Research Institute, The Scientific and Tech-nological Research Council of Turkey (TÜBITAK), 06531 Ankara, Turkey(e-mail: [email protected]; [email protected];[email protected]).

S. Buhan and I. Çadırcı are with Hacettepe University, 06532 Ankara,Turkey, and also with the Power Electronics Department, TÜBITAK UZAY Re-search Institute, The Scientific and Technological Research Council of Turkey(TÜBITAK), 06531 Ankara, Turkey (e-mail: [email protected]; [email protected]).

B. Boyrazoglu is with Renaissance Constructions, Moscow, Russia (e-mail:[email protected]).

T. Atalık is with Baskent University, 06530 Ankara, Turkey, and also with

the Power Electronics Department, TÜBITAK UZAY Research Institute, TheScientific and Technological Research Council of Turkey (TÜBITAK), 06531Ankara, Turkey (e-mail: [email protected]).

Ö. Ünsar is with Hacettepe University, 06532 Ankara, Turkey, and alsowith the Turkish Electricity Transmission Corporation (TEIAS), 06100 Ankara,Turkey (e-mail: [email protected]).

E. Altıntas is with the Middle East Technical University, 06531 Ankara,Turkey, and also with the Turkish Electricity Transmission Corporation(TEIAS), 06100 Ankara, Turkey (e-mail: [email protected]).

Y. Akkaya and E. Özdemirci are with the Turkish Electricity TransmissionCorporation (TEIAS), 06100 Ankara, Turkey (e-mail: [email protected]; [email protected]).

M. Ermis is with the Middle East Technical University, 06531 Ankara,Turkey (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TIA.2009.2036547

couplings where arc furnace installations are supplied. Based onthe field measurements obtained with collaborative work of fivearc furnace plants, it is possible to say that contemporary SVCsystems cause interharmonic amplification problems around thesecond harmonic, and novel methods are required to solve thisproblem.

Index Terms—Arc furnace, flicker, group harmonic,interharmonic–flicker relation, interharmonics, iron and steel

industry, ladle furnace, power quality (PQ), single-line harmonic,subgroup harmonic.

I. INTRODUCTION

THE iron and steel industry has been growing increasinglyin Turkey in the last decade. Today, its electricity demand

is nearly one-tenth of the installed generation capability of 40 GW in the country. Steel production in Turkey is based onextensive use of arc and ladle furnaces in most of the plants,which is the cause of power quality (PQ) problems at thoselocations of the Turkish Electricity Transmission System.

PQ of electric arc furnaces (EAF) has been investigated

previously by some other researchers [1]–[5]. Arc furnacecharacterization of one plant has been achieved in [1] in termsof PQ parameters given in the IEC standard 61000-4-30 [6]. In[2], different phases of EAF operation connected to the 13.5-kVvoltage level have been considered for obtaining a single-phaseequivalent circuit of the EAF.

In [3], the compatibility between the PQ disturbance levelsand the Argentinean regulations for EAF operation has beenconsidered. Measuring system accuracy for PQ of EAF instal-lations has been investigated in [4]. In [5], flicker propagationin the network based on interharmonic analysis on arc furnacesis introduced.

In this paper, we present very detailed and extensive investi-gations and results obtained from the PQ of arc furnace instal-lations in Turkey. The main focus is the investigation of the PQproblems caused by the iron and steel industry plants connecteddirectly to the Turkish Electricity Transmission System. Thecritical points of the transmission system are being monitoredby the mobile PQ monitoring systems developed through theNational Power Quality Monitoring Project [7]. By taking one-week snapshots of all PQ parameters specified in IEC 61000-4-30 [6], PQ of the iron and steel plants has been assessed.Based on this assessment, detailed investigation on the selectedfive plants supplied from the same busbar has been carriedout. Raw data of voltage and current waveforms have been

0093-9994/$26.00 © 2010 IEEE



2 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 46, NO. 1, JANUARY/FEBRUARY 2010

Fig. 1. Location of iron and steel plants on the Turkish Electricity Transmis-sion System.

collected for approximately 2 h at each plant based on a mea-surement schedule. This schedule requires collaborative workof all plants, since the arc furnace operation at the plants otherthan the measured one was stopped for 15 min. Contributionof the flicker and harmonics of each plant could be observedusing these measurements, while it is also possible to evaluatethe effectiveness or inefficiencies of the static-var-compensator(SVC)-type flicker compensation systems. It has been shownthat, with the common practices of compensation systems, it isnot possible to solve the flicker problem at the point of commoncoupling (PCC) from where arc furnaces are supplied.

Section II presents the general overview of the PQ of theiron and steel plants in Turkey. In Section III, description of theselected plants is given for detailed investigation. Measurementscenarios at those plants are presented in Section IV. InSection V, observations on the harmonic content of the EAFs onthe electric network are given. Sections VI and VII summarizethe harmonic computation methods used based on IEC 61000-4-30, and flicker–interharmonic relationship observations are

presented, respectively, from theoretical and experimental per-spectives. Assessment of the performance of SVC-type flickercompensation systems installed at EAF plants in terms of reactive power compensation, harmonic filtering performance,and flicker compensation performance is explained in detail inSection VIII. Section IX presents the PQ interaction of EAFs inmultifurnace operations.

II. COUNTRYWIDE PQ SNAPSHOT OF IRON

AN D STEEL PLANTS

Major iron and steel plants are marked on the map of the

Turkish Electricity Transmission System in Fig. 1. Steel pro-duction in only four of these plants is based on blast furnaces.At three points or regions of the Turkish Electricity System,multifurnace operation takes place. PQ of all of those plantshas been investigated based on the field measurements carriedout according to IEC 61000-4-30 for Class B performance byusing the mobile monitoring systems [7]. By the end of year2008, the National Power Quality Monitoring Center startedto operate for remote monitoring of the Turkish ElectricityTransmission System and its customers by permanent monitorsdesigned through the National Power Quality Project [8]. Thissystem will monitor the feeders of heavy industry, includingiron and steel plants, continuously.

The PQ measurements have been carried out at 400 kV, and154-kV PCCs for iron and steel plants. From the results of

Fig. 2. Long- and short-term flicker cumulative probability function for someplants connected to different PCCs at 400 kV.

the continuous PQ measurements lasting seven days at majortransformer substations supplying power to arc furnace plants,

the following problems have been identified.1) Although almost all of the plants are equipped with

modern SVC systems, measured flicker and current totaldemand distortion (current TDD) values exceed the limitsspecified in the Turkish Electricity Transmission SystemSupply Reliability and Quality Regulation [9], whichcomplies with the IEEE Std. 519-1992 [10]. The problemis more serious at transformer substations or busbarssupplying multiple arc furnaces as shown in Figs. 2–14.Cumulative probability function CPF(x) in the figuresindicates the percentage of the total measurement time forwhich the measured parameter is below a value x, given

in the horizontal axis. All harmonic analyses have beencarried out using the single-line harmonic componentsdirectly in this part of the work. Single-line harmonicfrequency concept is presented in IEC 61000-4-7 [11].Different harmonic analysis techniques given in [11]are summarized in Section VI. Since the power systemfrequency in Turkey is 50 Hz, ten-cycle Discrete FourierTransform (DFT) computation is used as suggested inIEC 61000-4-30 [6].

2) In all arc furnace installations, the second harmonic cur-rent component at the PCC exceeds the limit values evenafter filtration. Current waveforms of arc furnaces are richin interharmonics at low frequencies, particularly in melt-

ing state. For instance, the dominant flicker modulationfrequency of 8.8 Hz causes interharmonics in line current



SALOR et al.: ELECTRICAL POWER QUALITY OF IRON AND STEEL INDUSTRY IN TURKEY 3


Fig. 4. Second harmonic cumulative probability function for some plantsconnected to different PCCs at 154 kV.

Fig. 5. Third harmonic cumulative probability function for some plantsconnected to different PCCs at 154 kV.

Fig. 6. Fourth harmonic cumulative probability function for some plantsconnected to different PCCs at 154 kV.

Fig. 7. Fifth harmonic cumulative probability function for some plants con-nected to different PCCs at 154 kV.

Fig. 8. Primary current TDD cumulative probability function for some plants

connected to different PCCs at 154 kV.

waveforms at frequencies of f = 50k ± 8.8 Hz, wherek = 1, 2, 3, . . .. This fact has also been pointed out bysome other researchers [14], [15]. Some of these low-frequency interharmonic components in the line currentsare obviously amplified when attempted to be filtered outby C-type second harmonic and second-order third har-monic filters. On this occasion, the causes of undesirablyhigh values of voltage flicker, and current harmonics andinterharmonics at PCC have been investigated not onlyfor multi-furnace installations but also for single EAFoperation. The findings and the related discussion will

be reported in the following sections. Mitigation methodswill be discussed within the scope of another paper.




Fig. 9. Primary current TDD cumulative probability function for a plantconnected to a 154-kV PCC.

Fig. 10. Second harmonic cumulative probability function for a plant con-nected to a 400-kV PCC.

Fig. 11. Third harmonic cumulative probability function for a plant connectedto a 400-kV PCC.

III. DESCRIPTION OF SELECTED PLANTS

FO R DETAILED INVESTIGATION

As a result of these observations, five plants with arc furnaceinstallations which are supplied from the same busbar of thetransmission system are selected for further investigations onthe PQ parameters. These five plants are those on the westernside of Turkey (Izmir/Aliaga region), as shown on the map inFig. 1. Single-line diagram of the five plants is shown in Fig. 15.

IV. MEASUREMENT SCENARIOS

AT THE SELECTED PLANTS

The measurements at the five selected plants were organizedwith a collaborative effort of all plants. At each plant, raw

Fig. 12. Fourth cumulative probability function for a plant connected to a400-kV PCC.

Fig. 13. Fifth harmonic cumulative probability function for a plant connectedto a 400-kV PCC.

Fig. 14. Primary current TDD cumulative probability function for a plant

connected to a 400-kV PCC.

data of currents and voltages are recorded for approximately2 h. During this 2-h period, other four plants were organizedsuch that they stop furnace operation and their SVC systemsfor 15 min at the same time. Three-phase current and voltagemeasurements are collected at both the supply side and theplant side. Arc furnaces, ladle furnaces, where applicable, andSVC unit currents and voltages are recorded separately. Allmeasurements are synchronized by a GPS receiver module.This measurement process is repeated at each one of the fiveselected plants. Measurement points are as shown in Fig. 16.

The 15-min off period of the other plants connected to the

same bus guarantees that, during this period, if any currentharmonics or interharmonics are observed at the SVC unit




Fig. 15. Single-line diagram of the selected five plants.

Fig. 16. Synchronous measurement points at a typical EAF plant.

(Measurement Point 3) or the supply side of the plant (Measure-ment Point 1), those harmonics and interharmonics are mainlythe result of the EAF operation only at the measured plant.

This type of measurement can be used to understand whetherthe plant is a harmonic source or a harmonic sink on theelectricity transmission network, when the frequency spectraof the currents recorded with all plants in operation and with

four of them out of operation are compared. It is also possibleto detect any ineffectiveness of the SVCs at the measured plantusing the same comparison.

In order to observe the effectiveness of the SVC system, SVCof the current plants is turned off and on during the 15-minidle period of other plants and also when other plants are inoperation. This brings out four cases of measurements at everyplant: other plants on, SVC on; other plants on, SVC off;other plants off, SVC on; and other plants off, SVC off. Themeasurement periods are summarized in Table I. When thereare more than one arc furnace and ladle furnace at a plant, arcfurnaces and their SVCs other than the measured arc furnace

were turned off during the periods when other plants were off.This measurement scenario has been a very costly practice,

since the plants had to be turned off four times for a 15-minperiod, 1 h in total, while data were collected at every one of the other four plants. Moreover, turning off the SVC of themeasured plant was required twice: first while the other plantsare operative and second while they are inoperative. Moreover,turning off the SVCs causes inefficiencies of the EAF operation,which brings additional expenses.

V. ARC FURNACES AS HARMONIC SOURCES

ON THE NETWORK

EAF is the most problematic load on the electric network.Active and reactive power consumptions of an Ultra High

Power (UHP) EAF, together with its flicker compensation sys-tem, are shown in Fig. 17 over one tap-to-tap period. Furnacecharging, boring, melting, and refining periods are apparentfrom these records. Seven-day flicker and current TDD varia-tions of the same EAF + SVC installation (36 kV) are shownin Fig. 18.

IEC 61000-4-30 gives the ten-cycle (for 50-Hz systems)gapless harmonic and interharmonic subgroup measurement,denoted in IEC 61000-4-7 as the basic measurements for class-A performance.

In IEC-61000-4-7, however, three different methods of har-monic and interharmonic computation practices are given. Inthe case of fluctuating harmonics and interharmonics, thesethree methods give close but different results, which mayaffect the performance of spectrum estimations significantlyfor different cases of harmonic and interharmonic contents of the signal. These three computation methods are summarizedbriefly in the following.

1) Harmonic and interharmonic groups:

Harmonic group denoted by Gg,n is the square rootof the sum of the squares of a harmonic and the spec-tral components adjacent to it within the time window,such that

G2g,n =

C 2k−52

+4

i=−4

C 2k+i +C 2k+5

2(1)

for 50-Hz power systems, where C k is the rms of ampli-tude of the (k)th spectral component obtained from theDFT for the (n = k/10)th harmonic component. (Sincethe resolution is 5 Hz and the system frequency is 50 Hz,

every 10th DFT sample corresponds to a harmonic, i.e.,10th is the fundamental, 20th is the second harmonic, andso on.)

Similarly, interharmonic group is defined as

C 2ig,n =9

i=1

C 2k+i (2)

for 50-Hz power systems, where C k+i is the (k + i)thDFT sample, and they are the DFT samples between the(n)th and the (n + 1)th harmonics (for example, nineadjacent DFT samples between 55 and 95 Hz for theinterharmonics between second and third harmonics).

2) Harmonic and interharmonic subgroups:The harmonic grouping considers only the previousand the next DFT components around the harmonic com-ponent itself

G2sg,n =

1

i=−1

C 2k+i. (3)

In the interharmonic subgroup case, the effects of fluctuations of harmonic amplitudes and phases are par-tially reduced by excluding the components immediatelyadjacent to the harmonic frequencies

C 2isg,n =

8i=2

C 2k+i. (4)




TABLE IMEASUREMENT SCHEDULE (P HASES OF THE EAF: C—CHARGING, B—BORING, M—MELTING, AN D R—R EFINING)

Fig. 17. Active and reactive power consumptions of a UHP EAF together withits flicker compensation system in one tap-to-tap period (1-s averages).

3) Single-line harmonic frequency:

This is the single-line measurement of the current orvoltage frequency amplitude component obtained directlyfrom the 5-Hz-resolution DFT samples according to IEC61000-4-7.

The spectra in Figs. 19–21 are calculated from thecurrent data measured in boring, melting, and refining pe-riods, respectively. Fig. 22 shows a pictorial explanationof the harmonic and interharmonic group and subgroup

concepts. The spectrum in the figure is taken from thecurrent spectrum of the boring phase shown in Fig. 19.The harmonic and interharmonic group and subgroupvalues obtained from the current waveform in Fig. 19 aregiven in Table II.

As observed from Table II, there is a drastic differencebetween single line and subgroup, as well as single line andgroup harmonic current components particularly for the secondharmonic. However, IEEE Std 519-1992 and Turkish Std 2004[9] are not defined in the given current harmonic penalty limitswhether these are calculated as subgroup, group, or single-line components. This is the case for most of the research

papers given in the literature, as well. Therefore, the standardsmentioned earlier need to be revised so as to define the limit

Fig. 18. Seven-day(a) current TDD, (b) short-term flicker (P st), and (c) long-term flicker (P lt) variations of UHP EAF.

values according to IEC 61000-4-7 as harmonic subgroups. On

the other hand, in the design and performance assessment of SVC-type flicker compensation systems applied to the EAFs, it




Fig. 19. Ten-cycle waveform of the line current of the EAF during boringphase and its DFT with 5-Hz resolution.

Fig. 20. Ten-cycle waveform of the line current of the EAF during meltingphase and its DFT with 5-Hz resolution.

Fig. 21. Ten-cycle waveform of the line current of the EAF during refiningphase and its DFT with 5-Hz resolution.

is important to consider whether interharmonics and associatedharmonic components injected to the supply side are calculatedas single line or subgroup.

The rich interharmonic content between fundamental andsecond single-line harmonic frequency, and the lack of clarity

Fig. 22. Illustration of the harmonic and interharmonic group and subgroupcomputations.

TABLE IIHARMONIC AND INTERHARMONIC COMPUTATIONS FOR LIN E CURRENT

OF EAF IN BORING PHASE SHOWN IN FIG . 2 1

in the definition of harmonic limits brings together seriousdifficulties in the design and performance evaluation of passiveshunt second and third harmonic filters of SVC-type flickercompensation systems as will be discussed in Section VIII.

Measurements obtained at MP2 in Fig. 16 show that har-monic contents of EAFs are very rich. Particularly low ordercurrent harmonics such as second and third are observed tobe significant. Sample results for boring, melting, and refiningperiods of a High Power (HP) EAF are shown in Fig. 23.The richest harmonic content and TDD have been obtained forboring period. Since electric arc is highly stable during refining,the best harmonic content and TDD values have been obtainedfor the refining period.

VI. HARMONIC CONTENT COMPUTATION

BASED ON IEC 61000-4-7

The mobile systems collecting the voltage and current wave-

form data are sampling the data at a frequency of 3200 Hz. Thissampling rate corresponds to 64 samples per cycle; however,




Fig. 23. Sample results for boring, melting, and refining periods of an HP EAF (harmonic subgroups, ten-cycle averages with five-cycle overlapping windows).

when the supply frequency deviates from 50 Hz, a single cycleof the waveform is covered by more or less than 64 samples.This loss of synchronization causes leakage on the DFT sam-ples due to the picket fence effect [17]. According to IEC

61000-4-30, harmonics and interharmonics should be analyzedin ten-cycle windows which correspond to a frequency resolu-

tion of 5 Hz. With a constant sampling rate of 3200 Hz, the tenthDFT sample represents the 50-Hz component. When the systemfrequency is 49.5 Hz, for example, a leakage occurs from thetenth DFT sample toward the ninth DFT sample. This causes

an interharmonic to appear, although it does not exist in thesupply frequency. In this paper, a resampling process through




Fig. 24. Block diagram of the resampling process to sample ten cycles at640 equally spaced points.

interpolation is therefore achieved at every ten-cycle to preventthe leakage.

The algorithm is summarized in Fig. 24. Power cycles aredetected using a low-pass filter with a cutoff frequency at

75 Hz followed by a zero-crossing detection block. By usingthe zero-crossing points, data are split into ten-cycle blockswith rectangular windows. The ten-cycle blocks are resampledthrough cubic-spline interpolation such that each ten-cycle datablocks are sampled with a frequency of 64 samples/cycle.Each 640-sample block is the input to the DFT block, whichoutputs a 640-sample DFT output. In this case, the frequencyresolution of the DFT samples changes from the rate of 5 Hzto 64× f s/640 = f s/10, where f s is the supply frequency.The 10th DFT sample again corresponds to the first harmonicfrequency, which is f s, and 20th DFT sample corresponds tothe second harmonic. No leakage occurs from the harmonicfrequencies to the neighborhood interharmonic frequencies in

this case. This approach is used to obtain the harmonic andinterharmonic analyses of the voltage and current waveformspresented in Section VIII.

VII. FLICKER–I NTERHARMONIC RELATIONSHIP

The relationship between flicker and interharmonics has beeninvestigated previously, and it has been shown that flicker andinterharmonics are the causes of each other [14]–[16]. Lightflicker occurs when the voltage amplitude fluctuates in time.Therefore, flicker can be modeled as an amplitude-modulated(AM) signal whose carrier frequency is the 50-Hz supply

frequency as given in IEC 61000-4-15 [18]

y(t) = (A + m(t)) c(t)

= (A + M cos(wmt + φ)) sin(wct) (5)

where m(t) is the message signal, M is the amplitude of flicker,wm is the flicker frequency, wc is the power system frequency,and A is its amplitude. y(t) can also be expressed as

y(t) = A sin(wct) +M

2[sin ((wc + wm)t + ϕ)

+sin((wc − wm)t + φ)] . (6)

The fluctuation of the voltage amplitude shown in (5) causesthe interharmonic frequencies (wc + wm) and (wc −wm) to

Fig. 25. Time waveform of (9) with A = 1, M = 0.1, and the same 50-Hzsignal with 45- and 55-Hz interharmonics.

appear in the frequency spectrum of v(t) as shown in (6).In the case of any harmonics existing in the power system,interharmonics also appear around the harmonics as shown inthe example for a second harmonic in (7) and (8). For the sakeof simplicity, it is assumed that the fundamental and the secondharmonic are in phase in (7) and (8).

y(t) = (A+M cos(wmt+φ)) [sin(wct)+M 2 sin(2wct)] (7)

where AM 2 product is the amplitude of the second harmoniccomponent. y(t) can also be expressed as

y(t)

= A sin(wct)

+M

2[sin ((wc+wm)t+ϕ)+sin((wc−wm)t+φ)]

+AM 2 sin(2wct)MM 2

2

× [sin ((2wc+wm)t+ϕ)+sin((2wc−wm)t+φ)] . . . .

(8)

This shows that any voltage fluctuation, which can be ap-proximated as an AM, creates interharmonics around the fun-

damental and around the harmonics, if they exist. The reverseis also true, i.e., if there are interharmonics close to the funda-mental or the harmonics, they result in fluctuations in the signalamplitude.

In the case of any interharmonics occurring on only oneside of the fundamental or the harmonics, signal amplitudefluctuation also occurs. A single interharmonic at 55 Hz givencan be represented as an AM signal plus a low-amplitudeadditive signal at 45 Hz, as explained in the following equation:

y(t) =A sin(2π50t) + M sin(2π55t)

= (A + M cos(2π5t)) sin(2π50t)−M sin(2π55t). (9)

Time waveforms of the 50-Hz signal with amplitude 1 withadditive 10% 55-Hz interharmonic and with additive 45-Hz




Fig. 26. Sensitivity curve of the eye–brain set as a function of the frequencyof flicker.

interharmonic are shown in Fig. 25 up and down, respectively.Both interharmonics create similar voltage amplitude fluctua-tions. According to IEC 61000-4-15, human eye is the mostsensitive to the voltage fluctuations around 8.8 Hz. The sensi-tivity is reduced as the flicker frequency deviates up and downfrom 8.8 Hz, as shown in Fig. 26 [19]. Hence, interharmonicsapproximately 10 Hz apart from the fundamental and also fromthe harmonics give the highest contribution to the light flickerproblem.

Since experimentation on systems consisting of multi-EAFsis very expensive and flicker calculations need long-term mea-surements (one point for P st needs 10 min and one pointfor P lt needs 2 h), a close correlation between current andvoltage interharmonics in the range of 60–90 Hz (subgroupinterharmonic—1), which is the main cause of flicker, willbe very useful. This correlation permits indirect estimation of voltage flicker from the current interharmonic data collected for

a short time period. From the short-term current interharmonicdata, one can comment on the existence of flicker and alsoon the variation of it. As it can be observed from Figs. 19and 20, interharmonics around the fundamental are the mostdominant ones. Interharmonics around the second and thirdharmonics are also significant. Therefore, the variations involtage interharmonics between the first and second compo-nents (60–90 Hz) against current interharmonics can give usan idea about the mentioned correlation and, hence, the statusof the flicker. For various EAFs, voltage and current dataare simultaneously collected on the Medium Voltage (MV)side of the furnace transformer (at MP1 in Fig. 16), and a

sample interharmonic scattered diagram for Plant-5 is shownin Fig. 27. The bar charts of current interharmonic, voltageinterharmonic, and short-term flicker as a function of time atPlant-5 are shown in Fig. 28. These plots show that there is agood correlation between voltage and current interharmonics,and therefore, the variations in current interharmonic contentcan be used as a good indicator in estimating the state of theflicker.

For proper design of SVC-type flicker compensation sys-tems, the presence of these interharmonics should be takeninto consideration, particularly in the performance evaluation of existing passive shunt second- and third-order harmonic filters,as to be discussed in Section VIII.

In the evaluation of flicker contribution of each plant inmultiarc furnace operation, the harmonic and interharmonic

Fig. 27. Voltage interharmonic subgroup-1 versus current interharmonicsubgroup-1 (same data as in Fig. 28).

Fig. 28. (a) Current interharmonic subgroup-1 (10-min averages), (b) voltageinterharmonicsubgroup-1 (10-min averages), and (c) short-term flicker (10-minaverages) for Plant-5 during the whole measurement period.

spectra will be obtained for each plant separately for a time

duration of 10 min (for short-term flicker computation P st)when all other plants are off.




Fig. 29. Common harmonic filter topologies for SVC-type flicker compensa-tion systems. (a) SVC Type-1. (b) SVC Type-2. (c) SVC Type-3.

VIII. ASSESSMENT OF THE PERFORMANCE OF SVC-TYP EFLICKER COMPENSATION SYSTEMS

Practices of multinational SVC manufacturers can be sum-marized in three basic topologies shown in Fig. 29(a)–(c).The basic difference between SVCs in Fig. 29(a) and (b)is in the type of second harmonic filter. However, the SVCin Fig. 29(c) does not include any second harmonic filter.These three common practices of SVC-type flicker compen-sation systems will be investigated in this section in terms of reactive power performance, harmonic filtering performance,and flicker compensation performance by using synchronousdata collected in Plants 2, 3, and 5 according to the scenarios

described in Section IV.

A. Reactive Power Compensation Performance

It has been observed that SVC-type flicker compensationsystems perfectly compensate rapidly changing reactive powerdemand of EAFs. The mean power factor (PF) of an EAF canbe kept at nearly unity by a well-designed SVC.

B. Harmonic Filtering Performance

First, frequency characteristics of passive shunt harmonicfilters in Fig. 29 are obtained by using parameters given in

design documents of SVC manufacturers for Plants 2, 3, and 5.For this purpose, 1-A harmonic frequency is injected from the

Fig. 30. (a) Common-practice Type-1 model. (b) Frequency response of theSVC. (c) Field data frequency spectra of the EAF and supply currents of tencycles from boring phase of EAF.

EAF side, and the corresponding harmonic current componentreflected to the supply side is computed [see Figs. 30(a), 36(a),and 43(a)]. The current harmonic injected by EAF varies from50 to 400 Hz in 63× 10−4 steps. The resulting frequencycharacteristics, as an example, the one in Fig. 30(b), should beinterpreted in the following manner.

1) For harmonic frequencies f n, the magnitude greater than1 A in the supply side means an amplification, and lessthan 1 A means attenuation. These filter characteristicsmay be subjected to minor changes in time because of drift in capacitance values owing to aging.

2) For each SVC type, sample harmonic contents of linecurrents on both EAF side (MP2) and supply side (MP1)are calculated for ten-cycle window from synchronouslycollected data. The black-colored harmonic and interhar-monic bars (5-Hz resolution) show the EAF side, and thegray (or red) colored bars show the supply side. There-fore, for any harmonic frequency, if the gray-colored

bar is greater than the black-colored bar, the associatedharmonic is said to be amplified by SVC.




Fig. 31. Second harmonic single-line component EAF (I EAF) versus supply(I S) currents, when other plants are off and SVC of the plant is on.

3) The raw data are calculated for a short period as definedin Section IV when the other EAFs are off. Since the mostproblematic harmonic is the second harmonic component

for all SVC types, single-line harmonic, harmonic sub-group, and harmonic group computations for the secondharmonic component are given in three different forms. Inthe first group of plots, their variations are given againsttime in the form of 1-s average data. Here, again, theblack-colored curves correspond to the EAF-side current(MP2), and the gray-colored curves correspond to thesupply-side current (MP1). In the second group of char-acteristics, scattered diagrams for single line, harmonicsubgroup, and harmonic group for the second harmoniccomponent are given. Each point in a scattered diagramcorresponds to a ten-cycle window. For the harmoniccomponent higher than second (i.e., third, fourth, andfifth), the filtering performances of SVCs are illustratedby the curves in which the variations in each harmonicsubgroup are given against time. Here, again, the black-colored curves stand for EAF side, and the gray (or red)colored curves for supply side.

Below are the detailed analyses on the different SVC typesgiven in Fig. 29.

1) SVC Type-1: As it can be observed from Fig. 30(b), SVCType-1 amplifies all harmonics and interharmonics in the rangefrom 50 to 120 Hz. These expectations are confirmed from theexperimental data in Fig. 30(c) and Figs. 31–35. In scattereddiagrams, the diagonal of the graph, marked by a dashed line,

shows the case in which EAF harmonic is neither amplifiednor attenuated. Scattered points appearing densely above the

Fig. 32. Second harmonic subgroup component EAF (I EAF) versus supply(I S) currents, when other plants are off and SVC of the plant is on.

Fig. 33. Second harmonic group component EAF (I EAF) versus supply (I S)currents, when other plants are off and SVC of the plant is on.




Fig. 34. Third harmonic subgroup component EAF (I EAF) versus supply(I S) currents, when other plants are off and SVC of the plant is on.

Fig. 35. Fourth harmonic subgroup component EAF (I EAF) versus supply(I S) currents, when other plants are off and SVC of the plant is on.


diagonal mean that filtering performance of the harmonic underinvestigation is ineffective; that is, it amplifies EAF harmonicsto an extent observed from the associated scattered diagram. Asit can be seen from Figs. 34 and 35, SVC Type-1 filters out thethird and fourth harmonics, particularly the third one.

2) SVC Type-2: As it can be observed from Fig. 36(b),the ranges of 50–95 Hz, 105–125 Hz, and 160–175 Hz, allinterharmonics are amplified by the SVC. This is verified by the

field data shown in Fig. 36(c) and Figs. 37–39. It is observedthat the single-line harmonic points at 100 Hz are scatteredequally around the diagonal, which shows that this componentis usually not amplified. On the other hand, the subgroup andgroup harmonic computations show that a 100-Hz componentis amplified. This is due to the fact that, in subgroup andgroup computations, interharmonics around 100 Hz are alsoconsidered. As it can be seen from Figs. 40–42, SVC Type-2filters out the third, fourth, and fifth harmonic components,successfully.

3) SVC Type-3: As it can be observed from Fig. 43(b),SVC Type-3 amplifies all harmonics and interharmonics inthe range of 50–130 Hz. A drastic amplification of second

harmonic occurs. This is the undesirable effect of the second-order undamped third harmonic filter. This fact is verified by





the experimental data shown in Figs. 44–46 for all harmonic

computation types (single line, harmonic subgroup, and har-monic group). Third, fourth, and fifth harmonic components arefiltered out as it can be seen in Figs. 47–49, respectively.

Table III summarizes the harmonic filtering performanceof SVC-type flicker compensation systems according to thedata collected in the field. The existing common practice forSVCs cannot filter out the second harmonic subgroup, butamplifies it. However, harmonic subgroup higher than secondcan be filtered out successfully by a properly designed SVC.One should never forget the effects of Thyristor ControlledReactor (TCR) on the aforementioned harmonic curves. AnSVC operating in the steady state (at constant firing angle α)

creates only odd harmonics, excluding third and its powers,and the magnitudes of these harmonics are normally very low.However, in the transient states, i.e., in boring and meltingperiods, significant low harmonic components will also arisebecause of asymmetrical consecutive half current cycles andalso unbalanced third harmonic components. In summary, TCRharmonics are not necessarily in phase with EAF harmonics.When they are superimposed, a higher or a lower harmoniccontent than those of EAF may be obtained at all harmonicand interharmonic frequencies. In the previous harmonic char-acteristics and waveforms, TCR harmonics were not taken intoaccount. Experimental points scattered more than the expectedone may be attributed to the TCR harmonics. During the field

tests, it was not possible to disconnect only the TCR part of SVC from the network.

Fig. 42. Fifth harmonic subgroup component EAF (I EAF) versus supply(I S) currents, when other plants are off and SVC of the plant is on.

C. Flicker Compensation Performance

In Section VII, it has been shown that current and voltageinterharmonics are correlated, i.e., if there are current interhar-monics, then there are voltage interharmonics, and this leadsto light flicker. Since all three common practices of SVC-typeflicker compensation systems amplify the frequencies aroundsecond harmonics as shown in Figs. 30(b), 36(b), and 43(b), aflicker problem exists in all busbars supplying arc furnaces. Theamplification of interharmonics by the SVC system is shown inFigs. 50 and 51. In this particular experiment, the SVC systemof Plant-2 is turned off, while the other plants are off. Ten-cyclefirst interharmonics of both voltage and current (at MP1) arecomputed for this interval to observe the effect of the SVC on

the interharmonics and, hence, the light flicker. Although theSVC-type flicker compensation system is originally designedto reduce the flicker level, due to the improper design of theharmonic filters, (particularly the second harmonic filter), theSVC systems amplify the interharmonics around the secondharmonic, which causes the light flicker effect. This phenom-enon has been observed for all three common practices. It isobvious that a novel design approach is required for filteringthe second harmonic components.

IX. PQ INTERACTION BETWEEN EAFsIN MULTIFURNACE OPERATIONS

In order not to face a significant PQ problem, during theoperation of EAF and multi-EAFs, among the site selection





criteria in the planning and design phase of EAF installation(s),one of the most important criteria is the suitability and adequacyof the grid to which the EAF(s) is going to be connected. Thewell-known criteria in the selection of connection point to thegrid are as follows.

A. SCVD Method

Short-circuit voltage depression (SCVD) is usually ex-pressed as the percentage voltage drop at PCC when EAFgoes from open circuit to short circuit on all three phases.In order not to present a flicker problem, SCVD should be≤ 2% at voltages ≤ 132 kV and ≤ 1.6% at higher voltages(> 132 kV) [20]. SVCD value is directly proportional to thesum of source impedance, impedances of power transformerand EAF transformer, feeder impedance, reactance of seriesreactor if present, and EAF secondary circuit impedance.

In the planning phase, the most important contribution to thereduction of SCVD value is to connect EAF to one of the

strongest points of utility grid at the highest possible voltagelevel.









B. SCMVAmin/MV AEAF Ratio

In the literature, it is recommended by some researchers thatthe ratio of SCMVAmin (minimum value of Short CircuitMega Volt-Ampere) to the total arc furnace Mega Volt-Ampere(MVA) rating should not be lower than 80, while some otherssuggest that it should not be lower than 50, in order not to causeflicker, or to make the flicker problem solvable economically[12], [13]. For the multifurnace system shown in Fig. 15, thesecalculations have been made, and SCVD values are roughlyestimated to be as follows:

1) 1.74% SCVD if only the largest EAF is short circuited;2) 3.4% SCVD if two EAFs are simultaneously short

circuited;3) 6.6% SCVD if three EAFs are simultaneously short

circuited;4) 8.4% SCVD if all EAFs are simultaneously short

circuited.

It is shown that the recommended SCVD values will beexceeded in the case when more than one EAF are suppliedfrom the same point.SCMVAmin/MV AEAF ratio is found to be 70 even for the

smallest EAF. When all EAFs are considered, this ratio dropsto a dramatic value of 8. It is seen that a wrong planning hasobviously been made for iron and steel plants’ site containingmultifurnaces. On this occasion, it is not possible to solve the

flicker problem at PCC even to reduce it by the use of SVC-type flicker compensation systems because of the interactions





TABLE III

HARMONIC FILTERING PERFORMANCES OF THREE COMMON PRACTICES(F: FILTERED, A: AMPLIFIED)

between EAFs and amplifications of interharmonics by existingsecond harmonic or third filter as discussed in Section VIII.

The experimental results obtained from these plants provethese propositions indeed. Sample short-term (P st) and long-term (P lt) flicker values collected for seven-day time periodsfor multifurnace operation are shown in Fig. 52.

Obviously, P st and P lt values are much higher than the limitvalues given in the associated standards [9]. It is worth notingthat the SVC-type flicker compensation systems designed bymultinational companies have been in operation during themeasurement period. Despite these facts, these EAFs are oper-ating and producing millions of tones of steel every year. This

problem cannot be solved with current technology, but it can bemade less serious by reorganizing the structure of EAF power

Fig. 50. Interharmonic subgroup-1 of the voltage waveform from meltingphase of Plant-2 (ten-cycle averages with five-cycle overlaps).

Fig. 51. Interharmonic subgroup-1 of the current waveform from meltingphase of Plant-2 (ten-cycle averages with five-cycle overlaps).

Fig. 52. Seven-day flicker variation at PCC supplying multi-EAFs: (a) P stand (b) P lt.

system in this region. That is, nine EAFs in five iron and steelplants can be subdivided in the three groups for connection tothree different points of the utility grid. Furthermore, transmis-

sion voltage level at PCCs should be upgraded from 154 to400 kV. One further countermeasure is needed in reducing




flicker. That is, a new power plant installation with 1000-MWinstalled capacity seems to be inevitable in addition to theexisting two thermal plants and one natural gas plant locatedaround this region.

X. CONCLUSION

The following conclusions can be drawn from the results of intensive experimental work carried out in the field on bothsingle-furnace and multifurnace plants.

1) In order to avoid flicker, the most critical step is theplanning stage of EAF installations. For the candidateconnection point of EAF(s) to utility grid, first, simplecalculations of SCVD and SCMVAmin/MVAEAF ratioare to be carried out. These values should be safely lowerthan the recommended values, because after installationof SVC-type flicker compensation systems, flicker willnormally be increased.

2) An SVC-type flicker compensation system can compen-sate satisfactorily the rapidly changing reactive powerdemand of EAFs and keep the PF nearly at unity.

3) Passive shunt filters of carefully designed SVCs cansuccessfully filter out harmonic current components pro-duced by EAFs except second harmonic. The widelyapplied passive shunt filter topologies are experimentallyproven to lead to amplification of second harmonic sub-group and groups even to the amplification of single-linesecond harmonic component for many cases. In SVC-type flicker compensation systems, second harmonic filterseems to be integrated into the system not for the purposeof attenuation of the second harmonic component but

to limit its magnitude owing to the third harmonic filtermagnification.

4) In EAF installations, the major cause of the light flicker isinterharmonics around the existing harmonics. Therefore,interharmonics primarily between fundamental and sec-ond harmonic components, secondarily between secondand third harmonic components, are the causes of flicker.Since interharmonics between fundamental and secondharmonic components are significantly amplified by allwidely used passive filters, the operation of the SVC-type flicker compensation system is shown to increase theflicker level at PCC. Therefore, one can conclude that the

known SVC-type flicker compensation systems cannot bea solution to an existing flicker problem of single andmulti-EAF installations.

5) Because of the interaction between several SVCs andEAFs during multifurnace operation light flicker, in-terharmonics and second harmonic subgroup are morecomplex and usually more drastic in comparison withsingle EAF operation. The best approach to solve theseproblems is to avoid or minimize these risks in theplanning phase by selecting the most proper connectionpoint in the utility grid for EAF installation. To solveflicker, interharmonics, and second harmonic problems of the existing EAF installations, new active devices such

as active-power-filter D-STATCOM systems should beexercised.

ACKNOWLEDGMENT

The authors would like to thank the arc furnace plant au-thorities in the Izmir/Aliaga region of Turkey for supplyingthe opportunity of field measurements and their collaborativework of making the PCC measurements during various oper-ating conditions of the plants. This research and technology

development work is carried out as a subproject of the NationalPower Quality Project of Turkey.

REFERENCES

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Power Eng. Soc. General Meeting, 2005, pp. 784–791.[3] P. E. Issouribehere, J. C. Barbero, G. A. Barbera, and F. Issouribehere,

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O. Unsar, E. Altintas, B. Haliloglu, A. Acik, T. Atalik, Ö. Salor,T. Demirci, I. Cadirci, and M. Ermis, “Mobile monitoring system to takePQ snapshots of Turkish electricity transmission system,” in Proc. IEEE

IMTC , Warsaw, Poland, 2007, pp. 1–6.[8] T. Demirci, A. Kalaycıoglu, Ö. Salor, S. Pakhuylu, M. Dagh,

T. Kara, H. S. Aksuyek, C. Topcu, B. Polat, S. Bilgen, S. Umut,

I. Cadirci, and M. Ermis, “National PQ monitoring network for Turkishelectricity transmission system,” in Proc. IEEE IMTC , Warsaw, Poland,2007, pp. 1–6.

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flicker in electric arc furnace power systems,” IEEE Ind. Appl. Mag.,vol. 2, no. 1, pp. 28–38, Jan./Feb. 1996.

[14] T. Keppler, N. R. Watson, J. Arrillaga, and S. Chen, “Theoretical assess-ment of light flicker caused by sub- and interharmonic frequencies,” IEEE

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modulation,” IEEE Trans. Power Del., vol. 18, no. 2, p. 67,Apr. 2003.

[17] A. Testa, D. Gallo, and R. Langella, “On the processing of harmonics andinterharmonics: Using Hanning window in standard framework,” IEEE

Trans. Power Del., vol. 19, no. 1, pp. 28–34, Jan. 2004.[18] Testing and Measurement Techniques-Flickermeter- Functional and

Design Specifications, IEC 61000-4-15, 1998.[19] G. Diez, L. I. Eguiluz, M. Manana, J. C. Lavandero, and A. Ortiz,

“Instrumentation and methodology for revision of European flickerthreshold,” in Proc. 10th Int. Conf. Harmonics Quality Power , 2002,

pp. 262–265.[20] T. J. E. Miller, Reactive Power Control in Electric Systems. NewYork:Wiley-Interscience, 1982.




Özgül Salor (S’98–M’05) received the B.Sc., M.Sc.,and Ph.D. degrees in electrical engineering from theMiddle East Technical University, Ankara, Turkey, in1997, 1999, and 2005, respectively.

From 2001 to 2003, she was a Professional Re-searcher at the University of Colorado, Boulder.Since 2006, she has been with the Power ElectronicsDepartment, TÜBITAK UZAY Research Institute,

The Scientific and Technological Research Councilof Turkey (TÜBITAK), Ankara, where she is cur-rently a Chief Senior Researcher. She is also a part-

time Lecturer in the Department of Electrical and Electronics Engineering,Gazi University, Ankara. Her research interests are speech-signal processingand signal processing for power quality.

Burhan Gültekin (S’03) received the B.Sc. andM.Sc. degrees in electrical and electronics engi-neering from the Middle East Technical University,Ankara, Turkey, in 2000 and 2003, respectively,where he is currently working toward the Ph.D.degree.

He is currently a Chief Senior Researcher in thePower Electronics Department, TÜBITAK UZAYResearch Institute, The Scientific and TechnologicalResearch Council of Turkey (TÜBITAK), Ankara.His areas of research are in reactive power compen-

sation systems and power quality issues.

Serkan Buhan received the B.Sc. degree in elec-trical and electronics engineering from HacettepeUniversity, Ankara, Turkey, in 2005, where he iscurrently working toward the M.Sc. degree in powerquality.

He is currently a Researcher in the Power Elec-tronics Department, TÜBITAK UZAY Research In-stitute, The Scientific and Technological ResearchCouncil of Turkey (TÜBITAK), Ankara. His areasof research include power quality analysis usingwavelets.

Burak Boyrazoglu received the B.Sc. degree inelectrical and electronics engineering from theMiddle East Technical University, Ankara, Turkey,in 2005.

From 2006 to 2008, he was a Researcher in thePower Electronics Department, TÜBITAK UZAYResearch Institute, The Scientific and TechnologicalResearch Council of Turkey (TÜBITAK), Ankara.Currently, he is with Renaissance Constructions,Moscow, Russia.

Tolga Inan received the B.Sc. and M.Sc. degreesin electrical and electronics engineering from theMiddle East Technical University, Ankara, Turkey,in 2000 and 2003, respectively, where he is cur-rently working toward the Ph.D. degree in 3-D facerecognition.

He is currently a Senior Researcher in the PowerElectronics Department, TÜBITAK UZAY ResearchInstitute, The Scientific and Technological Research

Council of Turkey (TÜB˙ITAK), Ankara. His areasof research include pattern recognition, computer

vision, machine learning, and power quality analysis.

Tevhid Atalık received the B.Sc. degree in electricaland electronics engineering from Uludað University,Bursa, Turkey, in 2000, and the M.Sc. degree in elec-trical and electronics engineering from HacettepeUniversity, Ankara, Turkey, in 2003. He is currentlyworking toward the Ph.D. degree at Baskent Univer-sity, Ankara.

He is currently a Senior Researcher in the Power

Electronics Department, TÜBITAK UZAY ResearchInstitute, The Scientific and Technological ResearchCouncil of Turkey (TÜBITAK), Ankara. His areas of

research include power quality analysis and hardware design.

Adnan Açık received the B.Sc. and M.Sc. degreesin electrical and electronics engineering from theMiddle East Technical University, Ankara, Turkey,in 1995 and 1998, respectively.

He is currently a Chief Senior Researcher in thePower Electronics Department, TÜBITAK UZAYResearch Institute, The Scientific and Technological

Research Council of Turkey (TÜB˙ITAK), Ankara.His main areas of research are in power quality and

switch-mode power supplies.

Alper Terciyanlı (S’03) received the B.Sc. andM.Sc. degrees in electrical and electronics engi-neering from the Middle East Technical University,Ankara, Turkey, in 2001 and 2003, respectively,where he is currently working toward the Ph.D.degree in medium-voltage ac motor drives.

He is currently a Chief Senior Researcher in thePower Electronics Department, TÜBITAK UZAY

Research Institute, The Scientific and TechnologicalResearch Council of Turkey (TÜBITAK), Ankara.His areas of research include reactive power com-

pensation systems and power quality issues.

Özgür Ünsar (S’07) received the B.Sc. degreein electrical and electronics engineering from theMiddle East Technical University, Ankara, Turkey,in 2006. He is currently working toward the M.Sc.degree at Hacettepe University, Ankara.

He is currently a Researcher with the TurkishElectricity Transmission Corporation (TEIAS),

Ankara. His current areas of research include powerquality measurement and analysis.

Erinç Altıntas received the B.Sc. degree in elec-trical and electronics engineering from the MiddleEast Technical University, Ankara, Turkey, in 2006,where he is currently working toward the M.Sc.degree.

He is currently a Researcher with the TurkishElectricity Transmission Corporation (TEIAS),Ankara. His current areas of research include power

quality measurement and analysis.




Yener Akkaya receivedthe B.Sc. degreein electricaland electronics engineering from Istanbul Techni-cal University, Istanbul, Turkey, in 1989, and com-pleted the Public Administration Master Program atTODAIE, Ankara, Turkey, in 1997.

Since 1989, he has been with the Turkish Elec-tricity Transmission Corporation (TEIAS), Ankara,where he was with the Administration and Mainte-

nance Department and has been the Director of theResearch and Development Department since 2003.His current research interests are power quality and

transmission system planning.

Ercüment Özdemirci received the B.Sc. and M.Sc.degrees in electrical and electronics engineeringfrom Fýrat University, Elazýð, Turkey, in 1998 and2001, respectively.

From 1998 to 2003, he was with the Departmentof Load Dispatch, Turkish Electricity TransmissionCorporation (TEIAS), Ankara, Turkey, where he iscurrently in the Department of Transmission Plan-ning. His current research interests are power qual-ity, load-frequency control, and transmission systemplanning.

Isık Çadırcı (M’98) received the B.Sc., M.Sc.,and Ph.D. degrees in electrical and electronicsengineering from the Middle East TechnicalUniversity, Ankara, Turkey, in 1987, 1988, and 1994,respectively.

She is currently a Professor of electrical engi-neering at Hacettepe University, Ankara, and alsothe Head of the Power Electronics Department,

TÜBITAK UZAY Research Institute, The Scien-tific and Technological Research Council of Turkey(TÜBITAK), Ankara. Her areas of interest include

electric motor drives, switch-mode power supplies, and power quality.Dr. Çadırcı received the 2000 Committee Prize Paper Award from the Power

Systems Engineering Committeeof theIEEE Industry Applications Society andalso the IEEE Industry Applications Magazine Prize Paper Award, Third Prize,in 2007.

Muammer Ermis (M’99) received the B.Sc., M.Sc.,and Ph.D. degrees in electrical engineering from theMiddle East Technical University (METU), Ankara,Turkey, in 1972, 1976, and 1982, respectively, andthe M.BA. degree in production management fromAnkara Academy of Commercial and Economic Sci-ences, Ankara, in 1974.

He is currently a Professor of electrical engineer-ing at METU. He is also currently the Manager of the National Power Quality Project of Turkey. Hiscurrent research interest is electric power quality.

Dr. Ermis received the “The Overseas Premium” paper award from theInstitution of Electrical Engineers, U.K., in 1992, and the 2000 CommitteePrize Paper Award from the Power Systems Engineering Committee of theIEEE Industry Applications Society. He was the recipient of the 2003 IEEEPES Chapter Outstanding Engineer Award.



IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 46, NO. 1, JANUARY/FEBRUARY 2010 1

Electrical Power Quality of Ironand Steel Industry in Turkey

Özgül Salor, Member, IEEE , Burhan Gültekin, Student Member, IEEE , Serkan Buhan, Burak Boyrazoglu,

Tolga˙Inan, Tevhid Atalık, Adnan Açık, Alper Terciyanlı, Student Member, IEEE ,Özgür Ünsar, Student Member, IEEE , Erinç Altıntas, Yener Akkaya, Ercüment Özdemirci,

Isık Çadırcı, Member, IEEE , and Muammer Ermis, Member, IEEE

Abstract—The iron and steel industry has been growing increas-ingly in Turkey in the last decade. Today, its electricity demand isnearly one tenth of the installed generation capability of 40 GW inthe country. In this paper, power quality (PQ) investigations basedon the arc furnace installations of the iron and steel plants usingfield measurements according to the international standard IEC61000-4-30 are documented. Interharmonics and voltage flickerproblems occurring both at the common-coupling points of thoseplants and at the arc furnace and static var compensator (SVC)systems of the plants themselves are determined with the useof GPS receiver synchronization modules attached to the mobilePQ measurement systems. It has been observed that flicker andinterharmonic problems are dominant at the points of common

Paper PID-2009-04, presented at the 2007 Industry Applications SocietyAnnual Meeting, New Orleans, LA, September 23–27, and approved forpublication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS bythe Metals Industry Committee of the IEEE Industry Applications Society.Manuscript submitted for review November 30, 2007 and released for publi-cation June 22, 2009. This work was supported by the Public Research GrantCommittee (KAMAG) of The Scientific and Technological Research Councilof Turkey (TÜBITAK).

Ö. Salor and A. Açık are with the Power Electronics Department,

TÜB˙ITAK UZAY Research Institute, The Scientific and Technological Re-search Council of Turkey (TÜBITAK), 06531 Ankara, Turkey (e-mail: ozgul.

[email protected]; [email protected]).B. Gültekin, T. Inan, and A. Terciyanlı are with the Middle East Techni-

cal University, 06531 Ankara, Turkey, and also with the Power ElectronicsDepartment, TÜBITAK UZAY Research Institute, The Scientific and Tech-nological Research Council of Turkey (TÜBITAK), 06531 Ankara, Turkey(e-mail: [email protected]; [email protected];[email protected]).

S. Buhan and I. Çadırcı are with Hacettepe University, 06532 Ankara,Turkey, and also with the Power Electronics Department, TÜBITAK UZAY Re-search Institute, The Scientific and Technological Research Council of Turkey(TÜBITAK), 06531 Ankara, Turkey (e-mail: [email protected]; [email protected]).

B. Boyrazoglu is with Renaissance Constructions, Moscow, Russia (e-mail:[email protected]).

T. Atalık is with Baskent University, 06530 Ankara, Turkey, and also with

the Power Electronics Department, TÜBITAK UZAY Research Institute, TheScientific and Technological Research Council of Turkey (TÜBITAK), 06531Ankara, Turkey (e-mail: [email protected]).

Ö. Ünsar is with Hacettepe University, 06532 Ankara, Turkey, and alsowith the Turkish Electricity Transmission Corporation (TEIAS), 06100 Ankara,Turkey (e-mail: [email protected]).

E. Altıntas is with the Middle East Technical University, 06531 Ankara,Turkey, and also with the Turkish Electricity Transmission Corporation(TEIAS), 06100 Ankara, Turkey (e-mail: [email protected]).

Y. Akkaya and E. Özdemirci are with the Turkish Electricity TransmissionCorporation (TEIAS), 06100 Ankara, Turkey (e-mail: [email protected]; [email protected]).

M. Ermis is with the Middle East Technical University, 06531 Ankara,Turkey (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TIA.2009.2036547

couplings where arc furnace installations are supplied. Based onthe field measurements obtained with collaborative work of fivearc furnace plants, it is possible to say that contemporary SVCsystems cause interharmonic amplification problems around thesecond harmonic, and novel methods are required to solve thisproblem.

Index Terms—Arc furnace, flicker, group harmonic,interharmonic–flicker relation, interharmonics, iron and steel

industry, ladle furnace, power quality (PQ), single-line harmonic,subgroup harmonic.

I. INTRODUCTION

THE iron and steel industry has been growing increasinglyin Turkey in the last decade. Today, its electricity demand

is nearly one-tenth of the installed generation capability of 40 GW in the country. Steel production in Turkey is based onextensive use of arc and ladle furnaces in most of the plants,which is the cause of power quality (PQ) problems at thoselocations of the Turkish Electricity Transmission System.

PQ of electric arc furnaces (EAF) has been investigated

previously by some other researchers [1]–[5]. Arc furnacecharacterization of one plant has been achieved in [1] in termsof PQ parameters given in the IEC standard 61000-4-30 [6]. In[2], different phases of EAF operation connected to the 13.5-kVvoltage level have been considered for obtaining a single-phaseequivalent circuit of the EAF.

In [3], the compatibility between the PQ disturbance levelsand the Argentinean regulations for EAF operation has beenconsidered. Measuring system accuracy for PQ of EAF instal-lations has been investigated in [4]. In [5], flicker propagationin the network based on interharmonic analysis on arc furnacesis introduced.

In this paper, we present very detailed and extensive investi-gations and results obtained from the PQ of arc furnace instal-lations in Turkey. The main focus is the investigation of the PQproblems caused by the iron and steel industry plants connecteddirectly to the Turkish Electricity Transmission System. Thecritical points of the transmission system are being monitoredby the mobile PQ monitoring systems developed through theNational Power Quality Monitoring Project [7]. By taking one-week snapshots of all PQ parameters specified in IEC 61000-4-30 [6], PQ of the iron and steel plants has been assessed.Based on this assessment, detailed investigation on the selectedfive plants supplied from the same busbar has been carriedout. Raw data of voltage and current waveforms have been

0093-9994/$26.00 © 2010 IEEE




Fig. 1. Location of iron and steel plants on the Turkish Electricity Transmis-sion System.

collected for approximately 2 h at each plant based on a mea-surement schedule. This schedule requires collaborative workof all plants, since the arc furnace operation at the plants otherthan the measured one was stopped for 15 min. Contributionof the flicker and harmonics of each plant could be observedusing these measurements, while it is also possible to evaluatethe effectiveness or inefficiencies of the static-var-compensator(SVC)-type flicker compensation systems. It has been shownthat, with the common practices of compensation systems, it isnot possible to solve the flicker problem at the point of commoncoupling (PCC) from where arc furnaces are supplied.

Section II presents the general overview of the PQ of theiron and steel plants in Turkey. In Section III, description of theselected plants is given for detailed investigation. Measurementscenarios at those plants are presented in Section IV. InSection V, observations on the harmonic content of the EAFs onthe electric network are given. Sections VI and VII summarizethe harmonic computation methods used based on IEC 61000-4-30, and flicker–interharmonic relationship observations are

presented, respectively, from theoretical and experimental per-spectives. Assessment of the performance of SVC-type flickercompensation systems installed at EAF plants in terms of reactive power compensation, harmonic filtering performance,and flicker compensation performance is explained in detail inSection VIII. Section IX presents the PQ interaction of EAFs inmultifurnace operations.

II. COUNTRYWIDE PQ SNAPSHOT OF IRON

AN D STEEL PLANTS

Major iron and steel plants are marked on the map of the

Turkish Electricity Transmission System in Fig. 1. Steel pro-duction in only four of these plants is based on blast furnaces.At three points or regions of the Turkish Electricity System,multifurnace operation takes place. PQ of all of those plantshas been investigated based on the field measurements carriedout according to IEC 61000-4-30 for Class B performance byusing the mobile monitoring systems [7]. By the end of year2008, the National Power Quality Monitoring Center startedto operate for remote monitoring of the Turkish ElectricityTransmission System and its customers by permanent monitorsdesigned through the National Power Quality Project [8]. Thissystem will monitor the feeders of heavy industry, includingiron and steel plants, continuously.

The PQ measurements have been carried out at 400 kV, and154-kV PCCs for iron and steel plants. From the results of


the continuous PQ measurements lasting seven days at majortransformer substations supplying power to arc furnace plants,

the following problems have been identified.1) Although almost all of the plants are equipped with

modern SVC systems, measured flicker and current totaldemand distortion (current TDD) values exceed the limitsspecified in the Turkish Electricity Transmission SystemSupply Reliability and Quality Regulation [9], whichcomplies with the IEEE Std. 519-1992 [10]. The problemis more serious at transformer substations or busbarssupplying multiple arc furnaces as shown in Figs. 2–14.Cumulative probability function CPF(x) in the figuresindicates the percentage of the total measurement time forwhich the measured parameter is below a value x, given

in the horizontal axis. All harmonic analyses have beencarried out using the single-line harmonic componentsdirectly in this part of the work. Single-line harmonicfrequency concept is presented in IEC 61000-4-7 [11].Different harmonic analysis techniques given in [11]are summarized in Section VI. Since the power systemfrequency in Turkey is 50 Hz, ten-cycle Discrete FourierTransform (DFT) computation is used as suggested inIEC 61000-4-30 [6].

2) In all arc furnace installations, the second harmonic cur-rent component at the PCC exceeds the limit values evenafter filtration. Current waveforms of arc furnaces are richin interharmonics at low frequencies, particularly in melt-

ing state. For instance, the dominant flicker modulationfrequency of 8.8 Hz causes interharmonics in line current





Fig. 4. Second harmonic cumulative probability function for some plantsconnected to different PCCs at 154 kV.

Fig. 5. Third harmonic cumulative probability function for some plantsconnected to different PCCs at 154 kV.

Fig. 6. Fourth harmonic cumulative probability function for some plantsconnected to different PCCs at 154 kV.

Fig. 7. Fifth harmonic cumulative probability function for some plants con-nected to different PCCs at 154 kV.

Fig. 8. Primary current TDD cumulative probability function for some plants

connected to different PCCs at 154 kV.

waveforms at frequencies of f = 50k ± 8.8 Hz, wherek = 1, 2, 3, . . .. This fact has also been pointed out bysome other researchers [14], [15]. Some of these low-frequency interharmonic components in the line currentsare obviously amplified when attempted to be filtered outby C-type second harmonic and second-order third har-monic filters. On this occasion, the causes of undesirablyhigh values of voltage flicker, and current harmonics andinterharmonics at PCC have been investigated not onlyfor multi-furnace installations but also for single EAFoperation. The findings and the related discussion will

be reported in the following sections. Mitigation methodswill be discussed within the scope of another paper.




Fig. 9. Primary current TDD cumulative probability function for a plantconnected to a 154-kV PCC.

Fig. 10. Second harmonic cumulative probability function for a plant con-nected to a 400-kV PCC.

Fig. 11. Third harmonic cumulative probability function for a plant connectedto a 400-kV PCC.

III. DESCRIPTION OF SELECTED PLANTS

FO R DETAILED INVESTIGATION

As a result of these observations, five plants with arc furnaceinstallations which are supplied from the same busbar of thetransmission system are selected for further investigations onthe PQ parameters. These five plants are those on the westernside of Turkey (Izmir/Aliaga region), as shown on the map inFig. 1. Single-line diagram of the five plants is shown in Fig. 15.

IV. MEASUREMENT SCENARIOS

AT THE SELECTED PLANTS

The measurements at the five selected plants were organizedwith a collaborative effort of all plants. At each plant, raw

Fig. 12. Fourth cumulative probability function for a plant connected to a400-kV PCC.

Fig. 13. Fifth harmonic cumulative probability function for a plant connectedto a 400-kV PCC.

Fig. 14. Primary current TDD cumulative probability function for a plant

connected to a 400-kV PCC.

data of currents and voltages are recorded for approximately2 h. During this 2-h period, other four plants were organizedsuch that they stop furnace operation and their SVC systemsfor 15 min at the same time. Three-phase current and voltagemeasurements are collected at both the supply side and theplant side. Arc furnaces, ladle furnaces, where applicable, andSVC unit currents and voltages are recorded separately. Allmeasurements are synchronized by a GPS receiver module.This measurement process is repeated at each one of the fiveselected plants. Measurement points are as shown in Fig. 16.

The 15-min off period of the other plants connected to the

same bus guarantees that, during this period, if any currentharmonics or interharmonics are observed at the SVC unit




Fig. 15. Single-line diagram of the selected five plants.

Fig. 16. Synchronous measurement points at a typical EAF plant.

(Measurement Point 3) or the supply side of the plant (Measure-ment Point 1), those harmonics and interharmonics are mainlythe result of the EAF operation only at the measured plant.

This type of measurement can be used to understand whetherthe plant is a harmonic source or a harmonic sink on theelectricity transmission network, when the frequency spectraof the currents recorded with all plants in operation and with

four of them out of operation are compared. It is also possibleto detect any ineffectiveness of the SVCs at the measured plantusing the same comparison.

In order to observe the effectiveness of the SVC system, SVCof the current plants is turned off and on during the 15-minidle period of other plants and also when other plants are inoperation. This brings out four cases of measurements at everyplant: other plants on, SVC on; other plants on, SVC off;other plants off, SVC on; and other plants off, SVC off. Themeasurement periods are summarized in Table I. When thereare more than one arc furnace and ladle furnace at a plant, arcfurnaces and their SVCs other than the measured arc furnace

were turned off during the periods when other plants were off.This measurement scenario has been a very costly practice,

since the plants had to be turned off four times for a 15-minperiod, 1 h in total, while data were collected at every one of the other four plants. Moreover, turning off the SVC of themeasured plant was required twice: first while the other plantsare operative and second while they are inoperative. Moreover,turning off the SVCs causes inefficiencies of the EAF operation,which brings additional expenses.

V. ARC FURNACES AS HARMONIC SOURCES

ON THE NETWORK

EAF is the most problematic load on the electric network.Active and reactive power consumptions of an Ultra High

Power (UHP) EAF, together with its flicker compensation sys-tem, are shown in Fig. 17 over one tap-to-tap period. Furnacecharging, boring, melting, and refining periods are apparentfrom these records. Seven-day flicker and current TDD varia-tions of the same EAF + SVC installation (36 kV) are shownin Fig. 18.

IEC 61000-4-30 gives the ten-cycle (for 50-Hz systems)gapless harmonic and interharmonic subgroup measurement,denoted in IEC 61000-4-7 as the basic measurements for class-A performance.

In IEC-61000-4-7, however, three different methods of har-monic and interharmonic computation practices are given. Inthe case of fluctuating harmonics and interharmonics, thesethree methods give close but different results, which mayaffect the performance of spectrum estimations significantlyfor different cases of harmonic and interharmonic contents of the signal. These three computation methods are summarizedbriefly in the following.

1) Harmonic and interharmonic groups:

Harmonic group denoted by Gg,n is the square rootof the sum of the squares of a harmonic and the spec-tral components adjacent to it within the time window,such that

G2g,n =

C 2k−52

+4

i=−4

C 2k+i +C 2k+5

2(1)

for 50-Hz power systems, where C k is the rms of ampli-tude of the (k)th spectral component obtained from theDFT for the (n = k/10)th harmonic component. (Sincethe resolution is 5 Hz and the system frequency is 50 Hz,

every 10th DFT sample corresponds to a harmonic, i.e.,10th is the fundamental, 20th is the second harmonic, andso on.)

Similarly, interharmonic group is defined as

C 2ig,n =9

i=1

C 2k+i (2)

for 50-Hz power systems, where C k+i is the (k + i)thDFT sample, and they are the DFT samples between the(n)th and the (n + 1)th harmonics (for example, nineadjacent DFT samples between 55 and 95 Hz for theinterharmonics between second and third harmonics).

2) Harmonic and interharmonic subgroups:The harmonic grouping considers only the previousand the next DFT components around the harmonic com-ponent itself

G2sg,n =

1

i=−1

C 2k+i. (3)

In the interharmonic subgroup case, the effects of fluctuations of harmonic amplitudes and phases are par-tially reduced by excluding the components immediatelyadjacent to the harmonic frequencies

C 2isg,n =

8i=2

C 2k+i. (4)




TABLE IMEASUREMENT SCHEDULE (P HASES OF THE EAF: C—CHARGING, B—BORING, M—MELTING, AN D R—R EFINING)

Fig. 17. Active and reactive power consumptions of a UHP EAF together withits flicker compensation system in one tap-to-tap period (1-s averages).

3) Single-line harmonic frequency:

This is the single-line measurement of the current orvoltage frequency amplitude component obtained directlyfrom the 5-Hz-resolution DFT samples according to IEC61000-4-7.

The spectra in Figs. 19–21 are calculated from thecurrent data measured in boring, melting, and refining pe-riods, respectively. Fig. 22 shows a pictorial explanationof the harmonic and interharmonic group and subgroup

concepts. The spectrum in the figure is taken from thecurrent spectrum of the boring phase shown in Fig. 19.The harmonic and interharmonic group and subgroupvalues obtained from the current waveform in Fig. 19 aregiven in Table II.

As observed from Table II, there is a drastic differencebetween single line and subgroup, as well as single line andgroup harmonic current components particularly for the secondharmonic. However, IEEE Std 519-1992 and Turkish Std 2004[9] are not defined in the given current harmonic penalty limitswhether these are calculated as subgroup, group, or single-line components. This is the case for most of the research

papers given in the literature, as well. Therefore, the standardsmentioned earlier need to be revised so as to define the limit

Fig. 18. Seven-day(a) current TDD, (b) short-term flicker (P st), and (c) long-term flicker (P lt) variations of UHP EAF.

values according to IEC 61000-4-7 as harmonic subgroups. On

the other hand, in the design and performance assessment of SVC-type flicker compensation systems applied to the EAFs, it




Fig. 19. Ten-cycle waveform of the line current of the EAF during boringphase and its DFT with 5-Hz resolution.

Fig. 20. Ten-cycle waveform of the line current of the EAF during meltingphase and its DFT with 5-Hz resolution.

Fig. 21. Ten-cycle waveform of the line current of the EAF during refiningphase and its DFT with 5-Hz resolution.

is important to consider whether interharmonics and associatedharmonic components injected to the supply side are calculatedas single line or subgroup.

The rich interharmonic content between fundamental andsecond single-line harmonic frequency, and the lack of clarity

Fig. 22. Illustration of the harmonic and interharmonic group and subgroupcomputations.

TABLE IIHARMONIC AND INTERHARMONIC COMPUTATIONS FOR LIN E CURRENT

OF EAF IN BORING PHASE SHOWN IN FIG . 2 1

in the definition of harmonic limits brings together seriousdifficulties in the design and performance evaluation of passiveshunt second and third harmonic filters of SVC-type flickercompensation systems as will be discussed in Section VIII.

Measurements obtained at MP2 in Fig. 16 show that har-monic contents of EAFs are very rich. Particularly low ordercurrent harmonics such as second and third are observed tobe significant. Sample results for boring, melting, and refiningperiods of a High Power (HP) EAF are shown in Fig. 23.The richest harmonic content and TDD have been obtained forboring period. Since electric arc is highly stable during refining,the best harmonic content and TDD values have been obtainedfor the refining period.

VI. HARMONIC CONTENT COMPUTATION

BASED ON IEC 61000-4-7

The mobile systems collecting the voltage and current wave-

form data are sampling the data at a frequency of 3200 Hz. Thissampling rate corresponds to 64 samples per cycle; however,




Fig. 23. Sample results for boring, melting, and refining periods of an HP EAF (harmonic subgroups, ten-cycle averages with five-cycle overlapping windows).

when the supply frequency deviates from 50 Hz, a single cycleof the waveform is covered by more or less than 64 samples.This loss of synchronization causes leakage on the DFT sam-ples due to the picket fence effect [17]. According to IEC

61000-4-30, harmonics and interharmonics should be analyzedin ten-cycle windows which correspond to a frequency resolu-

tion of 5 Hz. With a constant sampling rate of 3200 Hz, the tenthDFT sample represents the 50-Hz component. When the systemfrequency is 49.5 Hz, for example, a leakage occurs from thetenth DFT sample toward the ninth DFT sample. This causes

an interharmonic to appear, although it does not exist in thesupply frequency. In this paper, a resampling process through




Fig. 24. Block diagram of the resampling process to sample ten cycles at640 equally spaced points.

interpolation is therefore achieved at every ten-cycle to preventthe leakage.

The algorithm is summarized in Fig. 24. Power cycles aredetected using a low-pass filter with a cutoff frequency at

75 Hz followed by a zero-crossing detection block. By usingthe zero-crossing points, data are split into ten-cycle blockswith rectangular windows. The ten-cycle blocks are resampledthrough cubic-spline interpolation such that each ten-cycle datablocks are sampled with a frequency of 64 samples/cycle.Each 640-sample block is the input to the DFT block, whichoutputs a 640-sample DFT output. In this case, the frequencyresolution of the DFT samples changes from the rate of 5 Hzto 64× f s/640 = f s/10, where f s is the supply frequency.The 10th DFT sample again corresponds to the first harmonicfrequency, which is f s, and 20th DFT sample corresponds tothe second harmonic. No leakage occurs from the harmonicfrequencies to the neighborhood interharmonic frequencies in

this case. This approach is used to obtain the harmonic andinterharmonic analyses of the voltage and current waveformspresented in Section VIII.

VII. FLICKER–I NTERHARMONIC RELATIONSHIP

The relationship between flicker and interharmonics has beeninvestigated previously, and it has been shown that flicker andinterharmonics are the causes of each other [14]–[16]. Lightflicker occurs when the voltage amplitude fluctuates in time.Therefore, flicker can be modeled as an amplitude-modulated(AM) signal whose carrier frequency is the 50-Hz supply

frequency as given in IEC 61000-4-15 [18]

y(t) = (A + m(t)) c(t)

= (A + M cos(wmt + φ)) sin(wct) (5)

where m(t) is the message signal, M is the amplitude of flicker,wm is the flicker frequency, wc is the power system frequency,and A is its amplitude. y(t) can also be expressed as

y(t) = A sin(wct) +M

2[sin ((wc + wm)t + ϕ)

+sin((wc − wm)t + φ)] . (6)

The fluctuation of the voltage amplitude shown in (5) causesthe interharmonic frequencies (wc + wm) and (wc −wm) to

Fig. 25. Time waveform of (9) with A = 1, M = 0.1, and the same 50-Hzsignal with 45- and 55-Hz interharmonics.

appear in the frequency spectrum of v(t) as shown in (6).In the case of any harmonics existing in the power system,interharmonics also appear around the harmonics as shown inthe example for a second harmonic in (7) and (8). For the sakeof simplicity, it is assumed that the fundamental and the secondharmonic are in phase in (7) and (8).

y(t) = (A+M cos(wmt+φ)) [sin(wct)+M 2 sin(2wct)] (7)

where AM 2 product is the amplitude of the second harmoniccomponent. y(t) can also be expressed as

y(t)

= A sin(wct)

+M

2[sin ((wc+wm)t+ϕ)+sin((wc−wm)t+φ)]

+AM 2 sin(2wct)MM 2

2

× [sin ((2wc+wm)t+ϕ)+sin((2wc−wm)t+φ)] . . . .

(8)

This shows that any voltage fluctuation, which can be ap-proximated as an AM, creates interharmonics around the fun-

damental and around the harmonics, if they exist. The reverseis also true, i.e., if there are interharmonics close to the funda-mental or the harmonics, they result in fluctuations in the signalamplitude.

In the case of any interharmonics occurring on only oneside of the fundamental or the harmonics, signal amplitudefluctuation also occurs. A single interharmonic at 55 Hz givencan be represented as an AM signal plus a low-amplitudeadditive signal at 45 Hz, as explained in the following equation:

y(t) =A sin(2π50t) + M sin(2π55t)

= (A + M cos(2π5t)) sin(2π50t)−M sin(2π55t). (9)

Time waveforms of the 50-Hz signal with amplitude 1 withadditive 10% 55-Hz interharmonic and with additive 45-Hz




Fig. 26. Sensitivity curve of the eye–brain set as a function of the frequencyof flicker.

interharmonic are shown in Fig. 25 up and down, respectively.Both interharmonics create similar voltage amplitude fluctua-tions. According to IEC 61000-4-15, human eye is the mostsensitive to the voltage fluctuations around 8.8 Hz. The sensi-tivity is reduced as the flicker frequency deviates up and downfrom 8.8 Hz, as shown in Fig. 26 [19]. Hence, interharmonicsapproximately 10 Hz apart from the fundamental and also fromthe harmonics give the highest contribution to the light flickerproblem.

Since experimentation on systems consisting of multi-EAFsis very expensive and flicker calculations need long-term mea-surements (one point for P st needs 10 min and one pointfor P lt needs 2 h), a close correlation between current andvoltage interharmonics in the range of 60–90 Hz (subgroupinterharmonic—1), which is the main cause of flicker, willbe very useful. This correlation permits indirect estimation of voltage flicker from the current interharmonic data collected for

a short time period. From the short-term current interharmonicdata, one can comment on the existence of flicker and alsoon the variation of it. As it can be observed from Figs. 19and 20, interharmonics around the fundamental are the mostdominant ones. Interharmonics around the second and thirdharmonics are also significant. Therefore, the variations involtage interharmonics between the first and second compo-nents (60–90 Hz) against current interharmonics can give usan idea about the mentioned correlation and, hence, the statusof the flicker. For various EAFs, voltage and current dataare simultaneously collected on the Medium Voltage (MV)side of the furnace transformer (at MP1 in Fig. 16), and a

sample interharmonic scattered diagram for Plant-5 is shownin Fig. 27. The bar charts of current interharmonic, voltageinterharmonic, and short-term flicker as a function of time atPlant-5 are shown in Fig. 28. These plots show that there is agood correlation between voltage and current interharmonics,and therefore, the variations in current interharmonic contentcan be used as a good indicator in estimating the state of theflicker.

For proper design of SVC-type flicker compensation sys-tems, the presence of these interharmonics should be takeninto consideration, particularly in the performance evaluation of existing passive shunt second- and third-order harmonic filters,as to be discussed in Section VIII.

In the evaluation of flicker contribution of each plant inmultiarc furnace operation, the harmonic and interharmonic

Fig. 27. Voltage interharmonic subgroup-1 versus current interharmonicsubgroup-1 (same data as in Fig. 28).

Fig. 28. (a) Current interharmonic subgroup-1 (10-min averages), (b) voltageinterharmonicsubgroup-1 (10-min averages), and (c) short-term flicker (10-minaverages) for Plant-5 during the whole measurement period.

spectra will be obtained for each plant separately for a time

duration of 10 min (for short-term flicker computation P st)when all other plants are off.




Fig. 29. Common harmonic filter topologies for SVC-type flicker compensa-tion systems. (a) SVC Type-1. (b) SVC Type-2. (c) SVC Type-3.

VIII. ASSESSMENT OF THE PERFORMANCE OF SVC-TYP EFLICKER COMPENSATION SYSTEMS

Practices of multinational SVC manufacturers can be sum-marized in three basic topologies shown in Fig. 29(a)–(c).The basic difference between SVCs in Fig. 29(a) and (b)is in the type of second harmonic filter. However, the SVCin Fig. 29(c) does not include any second harmonic filter.These three common practices of SVC-type flicker compen-sation systems will be investigated in this section in terms of reactive power performance, harmonic filtering performance,and flicker compensation performance by using synchronousdata collected in Plants 2, 3, and 5 according to the scenarios

described in Section IV.

A. Reactive Power Compensation Performance

It has been observed that SVC-type flicker compensationsystems perfectly compensate rapidly changing reactive powerdemand of EAFs. The mean power factor (PF) of an EAF canbe kept at nearly unity by a well-designed SVC.

B. Harmonic Filtering Performance

First, frequency characteristics of passive shunt harmonicfilters in Fig. 29 are obtained by using parameters given in

design documents of SVC manufacturers for Plants 2, 3, and 5.For this purpose, 1-A harmonic frequency is injected from the


EAF side, and the corresponding harmonic current componentreflected to the supply side is computed [see Figs. 30(a), 36(a),and 43(a)]. The current harmonic injected by EAF varies from50 to 400 Hz in 63× 10−4 steps. The resulting frequencycharacteristics, as an example, the one in Fig. 30(b), should beinterpreted in the following manner.

1) For harmonic frequencies f n, the magnitude greater than1 A in the supply side means an amplification, and lessthan 1 A means attenuation. These filter characteristicsmay be subjected to minor changes in time because of drift in capacitance values owing to aging.

2) For each SVC type, sample harmonic contents of linecurrents on both EAF side (MP2) and supply side (MP1)are calculated for ten-cycle window from synchronouslycollected data. The black-colored harmonic and interhar-monic bars (5-Hz resolution) show the EAF side, and thegray (or red) colored bars show the supply side. There-fore, for any harmonic frequency, if the gray-colored

bar is greater than the black-colored bar, the associatedharmonic is said to be amplified by SVC.





3) The raw data are calculated for a short period as definedin Section IV when the other EAFs are off. Since the mostproblematic harmonic is the second harmonic component

for all SVC types, single-line harmonic, harmonic sub-group, and harmonic group computations for the secondharmonic component are given in three different forms. Inthe first group of plots, their variations are given againsttime in the form of 1-s average data. Here, again, theblack-colored curves correspond to the EAF-side current(MP2), and the gray-colored curves correspond to thesupply-side current (MP1). In the second group of char-acteristics, scattered diagrams for single line, harmonicsubgroup, and harmonic group for the second harmoniccomponent are given. Each point in a scattered diagramcorresponds to a ten-cycle window. For the harmoniccomponent higher than second (i.e., third, fourth, andfifth), the filtering performances of SVCs are illustratedby the curves in which the variations in each harmonicsubgroup are given against time. Here, again, the black-colored curves stand for EAF side, and the gray (or red)colored curves for supply side.

Below are the detailed analyses on the different SVC typesgiven in Fig. 29.

1) SVC Type-1: As it can be observed from Fig. 30(b), SVCType-1 amplifies all harmonics and interharmonics in the rangefrom 50 to 120 Hz. These expectations are confirmed from theexperimental data in Fig. 30(c) and Figs. 31–35. In scattereddiagrams, the diagonal of the graph, marked by a dashed line,

shows the case in which EAF harmonic is neither amplifiednor attenuated. Scattered points appearing densely above the









diagonal mean that filtering performance of the harmonic underinvestigation is ineffective; that is, it amplifies EAF harmonicsto an extent observed from the associated scattered diagram. Asit can be seen from Figs. 34 and 35, SVC Type-1 filters out thethird and fourth harmonics, particularly the third one.

2) SVC Type-2: As it can be observed from Fig. 36(b),the ranges of 50–95 Hz, 105–125 Hz, and 160–175 Hz, allinterharmonics are amplified by the SVC. This is verified by the

field data shown in Fig. 36(c) and Figs. 37–39. It is observedthat the single-line harmonic points at 100 Hz are scatteredequally around the diagonal, which shows that this componentis usually not amplified. On the other hand, the subgroup andgroup harmonic computations show that a 100-Hz componentis amplified. This is due to the fact that, in subgroup andgroup computations, interharmonics around 100 Hz are alsoconsidered. As it can be seen from Figs. 40–42, SVC Type-2filters out the third, fourth, and fifth harmonic components,successfully.

3) SVC Type-3: As it can be observed from Fig. 43(b),SVC Type-3 amplifies all harmonics and interharmonics inthe range of 50–130 Hz. A drastic amplification of second

harmonic occurs. This is the undesirable effect of the second-order undamped third harmonic filter. This fact is verified by





the experimental data shown in Figs. 44–46 for all harmonic

computation types (single line, harmonic subgroup, and har-monic group). Third, fourth, and fifth harmonic components arefiltered out as it can be seen in Figs. 47–49, respectively.

Table III summarizes the harmonic filtering performanceof SVC-type flicker compensation systems according to thedata collected in the field. The existing common practice forSVCs cannot filter out the second harmonic subgroup, butamplifies it. However, harmonic subgroup higher than secondcan be filtered out successfully by a properly designed SVC.One should never forget the effects of Thyristor ControlledReactor (TCR) on the aforementioned harmonic curves. AnSVC operating in the steady state (at constant firing angle α)

creates only odd harmonics, excluding third and its powers,and the magnitudes of these harmonics are normally very low.However, in the transient states, i.e., in boring and meltingperiods, significant low harmonic components will also arisebecause of asymmetrical consecutive half current cycles andalso unbalanced third harmonic components. In summary, TCRharmonics are not necessarily in phase with EAF harmonics.When they are superimposed, a higher or a lower harmoniccontent than those of EAF may be obtained at all harmonicand interharmonic frequencies. In the previous harmonic char-acteristics and waveforms, TCR harmonics were not taken intoaccount. Experimental points scattered more than the expectedone may be attributed to the TCR harmonics. During the field

tests, it was not possible to disconnect only the TCR part of SVC from the network.


C. Flicker Compensation Performance

In Section VII, it has been shown that current and voltageinterharmonics are correlated, i.e., if there are current interhar-monics, then there are voltage interharmonics, and this leadsto light flicker. Since all three common practices of SVC-typeflicker compensation systems amplify the frequencies aroundsecond harmonics as shown in Figs. 30(b), 36(b), and 43(b), aflicker problem exists in all busbars supplying arc furnaces. Theamplification of interharmonics by the SVC system is shown inFigs. 50 and 51. In this particular experiment, the SVC systemof Plant-2 is turned off, while the other plants are off. Ten-cyclefirst interharmonics of both voltage and current (at MP1) arecomputed for this interval to observe the effect of the SVC on

the interharmonics and, hence, the light flicker. Although theSVC-type flicker compensation system is originally designedto reduce the flicker level, due to the improper design of theharmonic filters, (particularly the second harmonic filter), theSVC systems amplify the interharmonics around the secondharmonic, which causes the light flicker effect. This phenom-enon has been observed for all three common practices. It isobvious that a novel design approach is required for filteringthe second harmonic components.

IX. PQ INTERACTION BETWEEN EAFsIN MULTIFURNACE OPERATIONS

In order not to face a significant PQ problem, during theoperation of EAF and multi-EAFs, among the site selection





criteria in the planning and design phase of EAF installation(s),one of the most important criteria is the suitability and adequacyof the grid to which the EAF(s) is going to be connected. Thewell-known criteria in the selection of connection point to thegrid are as follows.

A. SCVD Method

Short-circuit voltage depression (SCVD) is usually ex-pressed as the percentage voltage drop at PCC when EAFgoes from open circuit to short circuit on all three phases.In order not to present a flicker problem, SCVD should be≤ 2% at voltages ≤ 132 kV and ≤ 1.6% at higher voltages(> 132 kV) [20]. SVCD value is directly proportional to thesum of source impedance, impedances of power transformerand EAF transformer, feeder impedance, reactance of seriesreactor if present, and EAF secondary circuit impedance.

In the planning phase, the most important contribution to thereduction of SCVD value is to connect EAF to one of the

strongest points of utility grid at the highest possible voltagelevel.









B. SCMVAmin/MV AEAF Ratio

In the literature, it is recommended by some researchers thatthe ratio of SCMVAmin (minimum value of Short CircuitMega Volt-Ampere) to the total arc furnace Mega Volt-Ampere(MVA) rating should not be lower than 80, while some otherssuggest that it should not be lower than 50, in order not to causeflicker, or to make the flicker problem solvable economically[12], [13]. For the multifurnace system shown in Fig. 15, thesecalculations have been made, and SCVD values are roughlyestimated to be as follows:

1) 1.74% SCVD if only the largest EAF is short circuited;2) 3.4% SCVD if two EAFs are simultaneously short

circuited;3) 6.6% SCVD if three EAFs are simultaneously short

circuited;4) 8.4% SCVD if all EAFs are simultaneously short

circuited.

It is shown that the recommended SCVD values will beexceeded in the case when more than one EAF are suppliedfrom the same point.SCMVAmin/MV AEAF ratio is found to be 70 even for the

smallest EAF. When all EAFs are considered, this ratio dropsto a dramatic value of 8. It is seen that a wrong planning hasobviously been made for iron and steel plants’ site containingmultifurnaces. On this occasion, it is not possible to solve the

flicker problem at PCC even to reduce it by the use of SVC-type flicker compensation systems because of the interactions





TABLE III

HARMONIC FILTERING PERFORMANCES OF THREE COMMON PRACTICES(F: FILTERED, A: AMPLIFIED)

between EAFs and amplifications of interharmonics by existingsecond harmonic or third filter as discussed in Section VIII.

The experimental results obtained from these plants provethese propositions indeed. Sample short-term (P st) and long-term (P lt) flicker values collected for seven-day time periodsfor multifurnace operation are shown in Fig. 52.

Obviously, P st and P lt values are much higher than the limitvalues given in the associated standards [9]. It is worth notingthat the SVC-type flicker compensation systems designed bymultinational companies have been in operation during themeasurement period. Despite these facts, these EAFs are oper-ating and producing millions of tones of steel every year. This

problem cannot be solved with current technology, but it can bemade less serious by reorganizing the structure of EAF power

Fig. 50. Interharmonic subgroup-1 of the voltage waveform from meltingphase of Plant-2 (ten-cycle averages with five-cycle overlaps).

Fig. 51. Interharmonic subgroup-1 of the current waveform from meltingphase of Plant-2 (ten-cycle averages with five-cycle overlaps).

Fig. 52. Seven-day flicker variation at PCC supplying multi-EAFs: (a) P stand (b) P lt.

system in this region. That is, nine EAFs in five iron and steelplants can be subdivided in the three groups for connection tothree different points of the utility grid. Furthermore, transmis-

sion voltage level at PCCs should be upgraded from 154 to400 kV. One further countermeasure is needed in reducing




flicker. That is, a new power plant installation with 1000-MWinstalled capacity seems to be inevitable in addition to theexisting two thermal plants and one natural gas plant locatedaround this region.

X. CONCLUSION

The following conclusions can be drawn from the results of intensive experimental work carried out in the field on bothsingle-furnace and multifurnace plants.

1) In order to avoid flicker, the most critical step is theplanning stage of EAF installations. For the candidateconnection point of EAF(s) to utility grid, first, simplecalculations of SCVD and SCMVAmin/MVAEAF ratioare to be carried out. These values should be safely lowerthan the recommended values, because after installationof SVC-type flicker compensation systems, flicker willnormally be increased.

2) An SVC-type flicker compensation system can compen-sate satisfactorily the rapidly changing reactive powerdemand of EAFs and keep the PF nearly at unity.

3) Passive shunt filters of carefully designed SVCs cansuccessfully filter out harmonic current components pro-duced by EAFs except second harmonic. The widelyapplied passive shunt filter topologies are experimentallyproven to lead to amplification of second harmonic sub-group and groups even to the amplification of single-linesecond harmonic component for many cases. In SVC-type flicker compensation systems, second harmonic filterseems to be integrated into the system not for the purposeof attenuation of the second harmonic component but

to limit its magnitude owing to the third harmonic filtermagnification.

4) In EAF installations, the major cause of the light flicker isinterharmonics around the existing harmonics. Therefore,interharmonics primarily between fundamental and sec-ond harmonic components, secondarily between secondand third harmonic components, are the causes of flicker.Since interharmonics between fundamental and secondharmonic components are significantly amplified by allwidely used passive filters, the operation of the SVC-type flicker compensation system is shown to increase theflicker level at PCC. Therefore, one can conclude that the

known SVC-type flicker compensation systems cannot bea solution to an existing flicker problem of single andmulti-EAF installations.

5) Because of the interaction between several SVCs andEAFs during multifurnace operation light flicker, in-terharmonics and second harmonic subgroup are morecomplex and usually more drastic in comparison withsingle EAF operation. The best approach to solve theseproblems is to avoid or minimize these risks in theplanning phase by selecting the most proper connectionpoint in the utility grid for EAF installation. To solveflicker, interharmonics, and second harmonic problems of the existing EAF installations, new active devices such

as active-power-filter D-STATCOM systems should beexercised.

ACKNOWLEDGMENT

The authors would like to thank the arc furnace plant au-thorities in the Izmir/Aliaga region of Turkey for supplyingthe opportunity of field measurements and their collaborativework of making the PCC measurements during various oper-ating conditions of the plants. This research and technology

development work is carried out as a subproject of the NationalPower Quality Project of Turkey.

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Özgül Salor (S’98–M’05) received the B.Sc., M.Sc.,and Ph.D. degrees in electrical engineering from theMiddle East Technical University, Ankara, Turkey, in1997, 1999, and 2005, respectively.

From 2001 to 2003, she was a Professional Re-searcher at the University of Colorado, Boulder.Since 2006, she has been with the Power ElectronicsDepartment, TÜBITAK UZAY Research Institute,

The Scientific and Technological Research Councilof Turkey (TÜBITAK), Ankara, where she is cur-rently a Chief Senior Researcher. She is also a part-

time Lecturer in the Department of Electrical and Electronics Engineering,Gazi University, Ankara. Her research interests are speech-signal processingand signal processing for power quality.

Burhan Gültekin (S’03) received the B.Sc. andM.Sc. degrees in electrical and electronics engi-neering from the Middle East Technical University,Ankara, Turkey, in 2000 and 2003, respectively,where he is currently working toward the Ph.D.degree.

He is currently a Chief Senior Researcher in thePower Electronics Department, TÜBITAK UZAYResearch Institute, The Scientific and TechnologicalResearch Council of Turkey (TÜBITAK), Ankara.His areas of research are in reactive power compen-

sation systems and power quality issues.

Serkan Buhan received the B.Sc. degree in elec-trical and electronics engineering from HacettepeUniversity, Ankara, Turkey, in 2005, where he iscurrently working toward the M.Sc. degree in powerquality.

He is currently a Researcher in the Power Elec-tronics Department, TÜBITAK UZAY Research In-stitute, The Scientific and Technological ResearchCouncil of Turkey (TÜBITAK), Ankara. His areasof research include power quality analysis usingwavelets.

Burak Boyrazoglu received the B.Sc. degree inelectrical and electronics engineering from theMiddle East Technical University, Ankara, Turkey,in 2005.

From 2006 to 2008, he was a Researcher in thePower Electronics Department, TÜBITAK UZAYResearch Institute, The Scientific and TechnologicalResearch Council of Turkey (TÜBITAK), Ankara.Currently, he is with Renaissance Constructions,Moscow, Russia.

Tolga Inan received the B.Sc. and M.Sc. degreesin electrical and electronics engineering from theMiddle East Technical University, Ankara, Turkey,in 2000 and 2003, respectively, where he is cur-rently working toward the Ph.D. degree in 3-D facerecognition.

He is currently a Senior Researcher in the PowerElectronics Department, TÜBITAK UZAY ResearchInstitute, The Scientific and Technological Research

Council of Turkey (TÜB˙ITAK), Ankara. His areasof research include pattern recognition, computer

vision, machine learning, and power quality analysis.

Tevhid Atalık received the B.Sc. degree in electricaland electronics engineering from Uludað University,Bursa, Turkey, in 2000, and the M.Sc. degree in elec-trical and electronics engineering from HacettepeUniversity, Ankara, Turkey, in 2003. He is currentlyworking toward the Ph.D. degree at Baskent Univer-sity, Ankara.

He is currently a Senior Researcher in the Power

Electronics Department, TÜBITAK UZAY ResearchInstitute, The Scientific and Technological ResearchCouncil of Turkey (TÜBITAK), Ankara. His areas of

research include power quality analysis and hardware design.

Adnan Açık received the B.Sc. and M.Sc. degreesin electrical and electronics engineering from theMiddle East Technical University, Ankara, Turkey,in 1995 and 1998, respectively.

He is currently a Chief Senior Researcher in thePower Electronics Department, TÜBITAK UZAYResearch Institute, The Scientific and Technological

Research Council of Turkey (TÜB˙ITAK), Ankara.His main areas of research are in power quality and

switch-mode power supplies.

Alper Terciyanlı (S’03) received the B.Sc. andM.Sc. degrees in electrical and electronics engi-neering from the Middle East Technical University,Ankara, Turkey, in 2001 and 2003, respectively,where he is currently working toward the Ph.D.degree in medium-voltage ac motor drives.

He is currently a Chief Senior Researcher in thePower Electronics Department, TÜBITAK UZAY

Research Institute, The Scientific and TechnologicalResearch Council of Turkey (TÜBITAK), Ankara.His areas of research include reactive power com-

pensation systems and power quality issues.

Özgür Ünsar (S’07) received the B.Sc. degreein electrical and electronics engineering from theMiddle East Technical University, Ankara, Turkey,in 2006. He is currently working toward the M.Sc.degree at Hacettepe University, Ankara.

He is currently a Researcher with the TurkishElectricity Transmission Corporation (TEIAS),

Ankara. His current areas of research include powerquality measurement and analysis.

Erinç Altıntas received the B.Sc. degree in elec-trical and electronics engineering from the MiddleEast Technical University, Ankara, Turkey, in 2006,where he is currently working toward the M.Sc.degree.

He is currently a Researcher with the TurkishElectricity Transmission Corporation (TEIAS),Ankara. His current areas of research include power

quality measurement and analysis.




Yener Akkaya receivedthe B.Sc. degreein electricaland electronics engineering from Istanbul Techni-cal University, Istanbul, Turkey, in 1989, and com-pleted the Public Administration Master Program atTODAIE, Ankara, Turkey, in 1997.

Since 1989, he has been with the Turkish Elec-tricity Transmission Corporation (TEIAS), Ankara,where he was with the Administration and Mainte-

nance Department and has been the Director of theResearch and Development Department since 2003.His current research interests are power quality and

transmission system planning.

Ercüment Özdemirci received the B.Sc. and M.Sc.degrees in electrical and electronics engineeringfrom Fýrat University, Elazýð, Turkey, in 1998 and2001, respectively.

From 1998 to 2003, he was with the Departmentof Load Dispatch, Turkish Electricity TransmissionCorporation (TEIAS), Ankara, Turkey, where he iscurrently in the Department of Transmission Plan-ning. His current research interests are power qual-ity, load-frequency control, and transmission systemplanning.

Isık Çadırcı (M’98) received the B.Sc., M.Sc.,and Ph.D. degrees in electrical and electronicsengineering from the Middle East TechnicalUniversity, Ankara, Turkey, in 1987, 1988, and 1994,respectively.

She is currently a Professor of electrical engi-neering at Hacettepe University, Ankara, and alsothe Head of the Power Electronics Department,

TÜBITAK UZAY Research Institute, The Scien-tific and Technological Research Council of Turkey(TÜBITAK), Ankara. Her areas of interest include

electric motor drives, switch-mode power supplies, and power quality.Dr. Çadırcı received the 2000 Committee Prize Paper Award from the Power

Systems Engineering Committeeof theIEEE Industry Applications Society andalso the IEEE Industry Applications Magazine Prize Paper Award, Third Prize,in 2007.

Muammer Ermis (M’99) received the B.Sc., M.Sc.,and Ph.D. degrees in electrical engineering from theMiddle East Technical University (METU), Ankara,Turkey, in 1972, 1976, and 1982, respectively, andthe M.BA. degree in production management fromAnkara Academy of Commercial and Economic Sci-ences, Ankara, in 1974.

He is currently a Professor of electrical engineer-ing at METU. He is also currently the Manager of the National Power Quality Project of Turkey. Hiscurrent research interest is electric power quality.

Dr. Ermis received the “The Overseas Premium” paper award from theInstitution of Electrical Engineers, U.K., in 1992, and the 2000 CommitteePrize Paper Award from the Power Systems Engineering Committee of theIEEE Industry Applications Society. He was the recipient of the 2003 IEEEPES Chapter Outstanding Engineer Award.

electrical power quality of iron and steel industry in turkey

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