97 c-type 2nd harmonic filter

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 47, NO. 4, JULY/AUGUST 2011 1545

Design, Implementation, and Operation of a NewC-Type 2nd Harmonic Filter forElectric Arc and Ladle Furnaces

Cem Özgür Gerçek, Student Member, IEEE, Muammer Ermis, Member, IEEE, Arif Ertas, Member, IEEE,Kemal Nadir Köse, and Özgür Ünsar, Student Member, IEEE

Abstract—In this paper, the transient overvoltage suppressioncapability and harmonic filtering performance of C-type 2ndharmonic filters (HFs) are optimized by using two-stage damp-ing resistors; one is permanently connected to the filter circuit,while the other one is switched on by back-to-back connectedthyristors during furnace transformer and HF energization peri-ods. However, in conventional C-type 2nd HFs, there is only onedamping resistor, which is permanently connected to the filtercircuit. In conventional designs, either the filtering performanceis maximized or transient overvoltage suppression capability isenhanced or a compromise is made between these two objectives.This new configuration of C-type 2nd HFs has been applied to asample iron and steel plant in which two ladle refining furnacesare in operation. For this purpose, an static var compensationsystem has been designed and installed, which is composed of athyristor-controlled reactor, a 3rd HF, and the new C-type 2ndHF configuration proposed in this paper. The results of field testsand simulation studies show that the proposed C-type 2nd HFconfiguration gives much better results than conventional designs.

Index Terms—C-type harmonic filter (HF), electric arc furnace(EAF), harmonics, interharmonics, ladle furnace, static var com-pensator (SVC).

I. INTRODUCTION

E LECTRIC arc furnaces (EAFs) and ladle refining fur-naces (LFs) in iron and steel plants are operated together

with static var compensation systems. Static var compensators(SVCs) are mostly composed of thyristor-controlled reactors(TCRs) and passive shunt harmonic filters (HFs). These SVC

Manuscript received January 17, 2011; accepted March 8, 2011. Date ofpublication May 16, 2011; date of current version July 20, 2011. Paper2011-METC-007, presented at the 2010 Industry Applications Society AnnualMeeting, Houston, TX, October 3–7, and approved for publication in theIEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Metals IndustryCommittee of the IEEE Industry Applications Society.

C. Ö. Gerçek is with the Electrical and Electronics Engineering Depart-ment, Middle East Technical University, 06531 Ankara, Turkey, and also withthe Power Electronics Department, TÜBITAK-UZAY, 06531 Ankara, Turkey(e-mail: [email protected]).

M. Ermis and A. Ertas are with the Electrical and Electronics EngineeringDepartment, Middle East Technical University, 06531 Ankara, Turkey (e-mail:[email protected]; [email protected]).

K. N. Köse was with the Power Electronics Department, TÜBITAK-UZAY,06531 Ankara, Turkey (e-mail: [email protected]).

Ö. Ünsar is with the Power Electronics Department, TÜBITAK-UZAY,06531 Ankara, Turkey (e-mail: [email protected]).

Digital Object Identifier 10.1109/TIA.2011.2155020

installations can satisfactorily compensate the rapidly changingreactive power demand of EAFs and LFs and keep the powerfactor at unity, thus maintaining the bus voltage. Normally,these SVCs are permanently connected to the power system. Atypical power system for EAF and LF installations is as shownin Fig. 1. Since EAFs and LFs are rapidly fluctuating nonlinearloads, the harmonic content of their line current waveforms isrich, including even and odd harmonics and interharmonics.Therefore, their HFs should be carefully designed in order tomeet the limit values specified in IEEE Standard 519-1992 [1].

Harmonic and transient overvoltage analyses and specialdesign considerations for HFs in EAF installations have beenpresented in [2] and [3]. Principles of filter selection andperformance evaluation have been described in [4]. Reference[5] gives an optimal planning algorithm for large HFs forhigh-voltage applications. Long-term overvoltages on industrialcapacitor banks, which may lead to destructive effects due to thetransformer energization inrush current, have been investigatedin [6]. The selection criteria for the voltage rating of shuntcapacitors are given in [3] and [7]–[10]. IEEE Standard 1531-2003 [11] is a valuable guide for determining the transientovervoltage capability of capacitors and selecting their voltageratings in view of harmonics and transformer inrush currentcomponents for EAF and LF applications.

Carefully designed passive shunt HFs can successfully fil-ter out harmonic current components produced by EAF andLF installations, except the 2nd harmonic component and 1stinterharmonic component [12]. The field data presented in[12] show that the common C-type 2nd HFs in commercialSVCs developed for EAF installations may even cause theamplification of 2nd harmonic current component. Therefore, anew approach to the configuration of C-type 2nd HF is neededto have a better filtering performance, as well as to prevent thefilter circuit elements from destructive effects of transformerinrush current harmonics in the long term.

II. PROBLEM DEFINITION

Conventional 2nd HF topologies are shown in Fig. 2. Thesecond-order damped filter in Fig. 2(b) has no practical use-fulness because of excessive power dissipation on the damp-ing resistor, owing to fundamental current. However, the HFsin Fig. 2(a) and (c) are commonly used in EAF and LF

0093-9994/$26.00 © 2011 IEEE

1546 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 47, NO. 4, JULY/AUGUST 2011

Fig. 1. Typical power system for EAF and LF installations.

Fig. 2. Conventional 2nd HF topologies. (a) Second-order undamped.(b) Second-order damped. (c) C-type.

applications. In this section, the effects of transformer inrushcurrent components on the 2nd HF elements as well as theperformance of HFs in EAF and LF installations in filtering outharmonics and interharmonics will be discussed.

A. Effects of Transformer Inrush on HF Elements

The tap-to-tap time of EAFs and LFs is in between30–60 minutes depending upon the furnace technology. Duringthe operation of the furnaces, time to time, owing to variousoperational reasons such as alloy additions to provide chemicalcontrol, temperature measurement, oxygen blowing, mainte-nance, etc., the furnace transformer is disconnected from themedium voltage (MV) furnace bus as a common practice andthen electrodes are lifted up. It means that, in each tap-to-tapperiod, the LF transformer is de-energized and then energizedseveral times for the safety of workers.

The operational statistics for a sample system show thatthe number of energizations of two LF transformers operatingconnected to a common bus is 150 per day on the average.This amounts to more than 50 000 LF transformer energizationsin each year. A sample record of LF transformer energization

when SVC is out of service is shown in Fig. 3. The fol-lowing observations are made from the waveforms in Fig. 3:1) very high peak current, 4.5 times greater than the rated peakvalue, just after energization and after a few cycles, saturationof the protection-type current transformer, owing to the highdc component [Fig. 3(a)]; 2) high dc component [Fig. 3(b)];3) high 2nd harmonic component [Fig. 3(c)]. This recordcorresponds to the worst case, and in Fig. 3(a), only theline current waveform which has the highest peak current isgiven. In Fig. 3(b) and (c), the fast Fourier transform (FFT)algorithm has been applied for ten-cycle windows according toIEC 61000-4-7 [13]. The ten-cycle windows are refreshed everyfull cycle, and in order to avoid leakage effects resulting fromfundamental frequency variations with respect to time, the fre-quency and, hence, the number of digital samples is calculatedfor each cycle, and then, the FFT window is updated accord-ingly. This adaptive algorithm is used throughout this paper.

If the elements of the C-type HF are not overdesigned, thehigh 2nd harmonic current component during transformer ener-gization may cause overloading of filter elements and may evenlead to destructive effects. As an example, the undesirable ef-fects of worst case energization on the elements of second-orderundamped 2nd HF shown in Fig. 2(a) are apparent from thewaveforms in Fig. 4, which are obtained by EMTDC/PSCADsimulations. Since the protection-type current transformer sat-urates a few cycles after the transformer energization, thetransformer inrush current record in Fig. 3(a) differs from thetheoretical waveform shown in Fig. 4.

B. Filtering Performance of HFs in EAF and LF Installations

EAFs and LFs are the most problematic industrial loads asharmonic and flicker sources on the network. IEC 61000-4-30[14] gives the ten-cycle (for 50-Hz systems) gapless har-monic and interharmonic subgroup measurements denoted in

GERÇEK et al.: DESIGN, IMPLEMENTATION, AND OPERATION OF NEW C-TYPE 2ND HF 1547

Fig. 3. LF transformer energization without SVC (field data). (a) Line currenton the transformer primary, Is. (b) DC and fundamental component of Is.(c) Other harmonic subgroups of Is.

IEC 61000-4-7 [13] as the basic measurements for Class-Aperformance. However, three different methods of harmonicand interharmonic computation practices are given in [13].These are as follows: 1) harmonic and interharmonic groups;2) harmonic and interharmonic subgroups; and 3) single-lineharmonic frequencies, as shown in Fig. 19 in Appendix A.

In the case of fluctuating harmonics and interharmonics pro-duced by EAFs and LFs, these three methods give drasticallydifferent results, which may significantly affect the perfor-mance of spectrum estimations for different cases of harmonicand interharmonic contents of the signal.

The maximum permissible values of short-term flicker (Pst)and long-term flicker (Plt) are specified in IEC 61000-4-15[15]. On the other hand, the maximum permissible valuesfor voltage harmonics and total harmonic distortion and themaximum permissible values for current harmonics and totaldemand distortion are as defined in [1] and [16]. However,in these standards, the calculation method such as single line,subgroup, or group components is not specified. Therefore, thestandards aforementioned need to be revised so as to definelimit values according to [13] as harmonic subgroups. On thisoccasion, in this paper, the performance of the proposed C-type

Fig. 4. LF transformer energization with second-order undamped filter(simulation data).

2nd HF will be compared with those of conventional designs inview of all three harmonic computation practices.

The practices of multinational SVC manufacturers can besummarized in the three basic SVC-type flicker compensationsystem topologies shown in Figs. 20–22 in Appendix B [12].An intensive experimental work carried out in the field on bothsingle- and multifurnace plants and reported in [12] had shownthat the following are true.

1) Passive shunt filters of these SVCs cannot filter out 2ndharmonic and 1st interharmonic current components pro-duced by EAFs but usually amplify them [Figs. 20(c) and22(c)].

2) In EAF installations, the major cause of the light flickeris voltage interharmonics around the existing harmonics.Subharmonics (components below 50 Hz) and the har-monic components between 50 and 100 Hz are the maincauses of flicker. Since interharmonics between funda-


Fig. 5. Proposed configuration for C-type 2nd HF.

mental and 2nd harmonic components are significantlyamplified by all widely used passive filters, the operationof the SVC-type flicker compensation system is shown toincrease the flicker level at MV furnace bus.

Therefore, new active devices such as active power filterand D-STATCOM systems should be exercised in order tosolve flicker, interharmonic, and 2nd harmonic problems ofthe existing EAF installations entirely. A cheaper and simplerpartial solution to the same problem is to use a new C-type 2ndHF as proposed in this paper instead of conventional 2nd HFdesigns in TCR-type SVCs.

III. PROPOSED CONFIGURATION FOR C-TYPE 2ND HF

A. Proposed HF Configuration and Description of Sample LFInstallation

In this paper, the C-type 2nd HF configurations shown inFig. 5 are proposed in order to optimize the filtering perfor-mance, to minimize the magnitudes of voltages and currentsimposed on filter elements in the transient state, and to re-duce the steady-state power dissipation. This is achieved bydesigning and operating the damping resistor RD connectedacross the L−C1 filter branch in Fig. 1 in two steps. In thesample application, the configuration in Fig. 5(a) is imple-mented, because it fits perfectly to the existing lightly dampedC-type HFs. However, the configuration in Fig. 5(b) can beused only in new C-type 2nd HF installations. It requiresa special damping resistor in two parts. RD in Fig. 5(a) ispermanently connected to the filter circuit to provide a lowelectrical damping during the operation of the furnace/s. Thisway, the filtering performance of C-type 2nd HF is plannedto be optimized in comparison with conventional designs.However, during transformer energization or connection of HFsto the SVC bus, high electrical damping is needed in order toreduce the stresses on the elements of HFs. This is achieved byconnecting a low resistance RTS in Fig. 5(a) across RD duringthe energization for a short time period, i.e., three seconds inthe sample application (Fig. 6). This yields a smaller resistancethan RTS in transient state, RD//RTS (RD in parallel withRTS).

In the static switches, either conventional thyristors (SCRs)or light-triggered thyristors (LTTs) can be employed. LTTs

Fig. 6. New C-type 2nd HF.

are more suitable for outdoor applications, because they donot need external firing circuits. Since the damping resistorRTS is connected to the C-type filter by triggering back-to-back connected thyristors into conduction, a small inductancein series with RTS is needed in order to limit di/dt. In thesample application, this is achieved by using sufficiently longpower cables, which should give a minimum inductance of15 μH in each line.

The triggering command for static switches in Fig. 5(a) toconnect RTS to the C-type filter can be generated in one of thefollowing ways.

1) A signal can be taken from the transformer circuit-breakerrelay which gives a command to the circuit-breaker toclose.

2) Whenever the voltage across C2 tends to exceed a pre-specified threshold, back-to-back thyristors can be trig-gered into conduction. This makes necessary the use of aspecial measurement-type voltage transformer such as aresistive capacitive voltage transformer which is capableof measuring both ac and dc.

3) Whenever the line current of the C-type filter tends toexceed a prespecified threshold value, thyristors can betriggered into conduction.

4) Whenever the current in the RD in Fig. 5(a) tends toexceed a prespecified threshold value, thyristors can betriggered into conduction.

In the implementation, the last method has been preferredbecause it allows the measurement of current in RD, and hence,its continuous power dissipation. In the sample application fortwo LFs operating connected to the same bus, five consecutiveswitchings of RTS are assumed, which is equivalent to keepingthe thyristor stacks in conduction for a 15 seconds time period.Since the power dissipation of thyristors in conduction stateis quite low, the semiconductor cooling problem is solved byusing simple and cheap bar-type flat heatsinks with sufficientheat storage capacity instead of more expensive natural orforced air-cooled heatsinks with fins or deionized water-basedcooling system.


Fig. 7. Sample LF installation (RD = 250 Ω, RTS = 18 Ω, C1 = 714 μF, C2 = 274 μF, and L = 14.25 mH).

Fig. 8. Reactor–capacitor–resistor yard.

B. Description of the Sample Application

This new C-type 2nd HF configuration has been designedfor, implemented, and operated in a sample system, as shownin Fig. 7 (ERDEMIR Iron and Steel Company which is anintegrated steel plant). The configuration in Fig. 5(a) is chosenfor the implementation. This is because it has a more flexiblestructure for refurbishment works that can be made on con-ventional C-type 2nd HFs existing in various iron and steelplants. General views of the overall SVC system are shownin Figs. 6, 8, and 10. This system has been developed by theauthors of this paper within the scope of a contracted SVCproject signed between the Power Electronics Department ofTÜBITAK-UZAY Research Institute and ERDEMIR Company.The damping resistors RTS in Figs. 5(a) and 6, which providehigh electrical damping, are switched on by LTTs in Fig. 9,while the shunt reactors are controlled by electrically triggeredthyristors in Fig. 10.

Fig. 9. LTT stacks.

Fig. 10. Power stacks and control system.


Fig. 11. Definitions of ERD, PRD(max), PRD(s.s), VC2p(max), andVC2p(s.s) for conventionally designed C-type 2nd HF. (a) Damping resistorcurrent, iRD. (b) Damping resistor power loss, PRD. (c) C2 peak voltage,VC2p.

Fig. 12. Effects of RD in Fig. 1 on power and energy loss in RD and voltageacross C2 (simulation results).

C. Design

In this section, the design principles of RD, RTS, and C2

will be described, and their values for the sample applicationwill be determined by considering the resulting C-type filterperformance during transformer energization and also for nor-mal operating period of LFs. For the conventional C-type 2ndHF in Fig. 1, maximum instantaneous power dissipation onRD (PRD(max)), energy dissipation on RD (ERD), and max-imum peak voltage on C2 (VC2p(max)) during LF transformer

Fig. 13. Filtering performance of various conventionally designed 2nd HFs(black-colored bars are the worst case furnace data, and gray-colored bars arethe corresponding harmonics reflected to the supply side). (a) Second-orderundamped 2nd HF + second-order undamped 3rd HF. (b) C-type 2nd HF(lightly damped) + second-order undamped 3rd HF. (c) C-type 2nd HF (highlydamped) + second-order undamped 3rd HF.

energization and also power dissipation on RD in the steadystate (PRD(s.s)) are as defined in Fig. 11. Fig. 11(a) showstypical variations in current through RD after transformer en-ergization, which is recorded in the field on the sample systemwith RD = 250 Ω.


Fig. 14. Harmonic and interharmonic evaluation of proposed C-type 2nd HF in comparison with conventional designs.

For the sample system in Fig. 7, RD is varied in the rangefrom 10 to 500 Ω and the variations in power and energy lossin RD and peak voltage across C2 are calculated by usingEMTDC/PSCAD. These are shown in Fig. 12.

As can be observed from Fig. 12, a damping resistorwith a resistance in the range from 10 to 20 Ω signifi-cantly reduces VC2p(max) and keeps PRD(max) and ERD

at reasonably low values during the energization of the LF


Fig. 15. Voltage on C2 during filter energization (worst case). (a) RD =250 Ω and RTS = ∞. (b) RD = 250 Ω//RTS = 18 Ω.

transformer. Therefore, RTS in Fig. 7 is chosen to be 18 Ωand kept connected to the circuit for three seconds bythyristor switches during the LF transformer or SVC ener-gization. The parallel combination of permanently connectedresistor RD in Fig. 5(a) and RTS = 18 Ω gives an equiv-alent damping resistance RDeq which is less than 18 Ωin the transient state. Since shunt capacitors can withstand1.1 times the rated voltage with a 50% duty cycle as specifiedin IEC 60871-1 [8], the rated peak voltage of C2 can be chosenas the maximum permissible peak value of the bus voltage topermit theoretically infinitely many switchings. On the otherhand, during the normal operation after disconnecting RTS inFig. 5(a) from the filter, the optimum value of the permanentlyconnected damping resistor RD in Fig. 5(a) should be chosenin view of the following constraints.

1) PRD(s.s.) in Fig. 12(b) is to be minimized, and hence, RD

should not be chosen less than 250 Ω.2) The filtering performance of the C-type filter should be

optimized when the two LFs in Fig. 7 are in operation.The filtering performance of conventional C-type designs

will be improved by determining optimum values of tuningfrequency and permanently connected damping resistor RD.Current transfer characteristics and filtering performances of

Fig. 16. Operation of solid-state switches. (a) RD current, iRD. (b) RTS

current, iRTS

conventionally designed 2nd HFs together with a second-order3rd HF are as shown in Fig. 13. These 2nd HFs are tuned to100 Hz. The following conclusions can be drawn from thesecharacteristics:

1) a 100-Hz tuning frequency causes significant amplifica-tion of 90- and 95-Hz single-line harmonic frequencies;

2) 100- and 105-Hz single-line harmonics are perfectly fil-tered out by the undamped [Fig. 13(a)] and the lightlydamped [Fig. 13(b)] HFs;

3) the amplification in the 1st interharmonic group andsubgroup for heavily damped case is lower than those ofundamped and lightly damped cases.

Therefore, in the design of the new C-type 2nd HF, thetuning frequency is shifted to 95 Hz in order to improvefiltering performance for the 2nd harmonic subgroup (92.5–107.5 Hz; for their exact expressions, refer to IEC 61000-4-7[13]).

The worst case harmonic spectra for the LFs and the cor-responding harmonics reflected to the supply after connectingvarious conventionally designed 2nd HFs and two differentdesigns of new C-type 2nd HF are shown in Fig. 14. Theirsingle-line harmonic magnitudes, 2nd harmonic group andsubgroup values, and 1st interharmonic group and subgroupvalues are also marked on the same figure. These figures showthe following.

1) The proposed C-type 2nd HF avoids the amplificationrisk of the 2nd harmonic subgroup. Nearly 15% of thefurnace current is shown to be filtered out; however, theconventional designs may result in an amplification factorin the range from 5% to 40%, depending on the strengthof the electrical damping.

2) Shifting the tuning frequency from 100 to 95 Hz doesnot make a significant contribution to the attenuation of100- and 105-Hz single-line harmonics.


Fig. 17. Transformer inrush effects (field data) for (i) 250//18 Ω and (ii) only 250 Ω in conduction.

3) In both types of designs, 1st interharmonic group isamplified nearly by 7% while the amplification factorsof the 1st interharmonic subgroup for the new designs areslightly higher than those of conventional designs.

In the new design approach, the C-type 2nd HF is tuned to95 Hz. There remains only the determination for the optimumvalue of RD of the permanently connected damping resistor. Ascan be understood from Fig. 14(v) and (vi), the RD = 500 Ωcase gives the higher 2nd harmonic group, 1st interharmonicgroup, and subgroup values in comparison with the RD =250 Ω case although its attenuation for the 2nd harmonicsubgroup is better. Therefore, RD = 250 Ω is chosen in theimplementation. This yields an equivalent damping resistanceRDeq = 250//18 = 16.7 Ω in the transient state.

HFs are rarely disconnected from and reconnected to MVEAF or LF bus in comparison with transformers. The responseof the proposed C-type filter during connection to the MVbus is obtained by EMTDC/PSCAD and shown in Fig. 15in comparison with that of a lightly damped conventionalC-type. Fig. 15(b) shows that the proposed design yields much

better transient response. In fact, both design approaches meetsuccessfully maximum permissible power frequency capacitorovervoltage limits specified in IEEE Standard 18-1992 [10].

IV. RESULTS AND DISCUSSION

The performance of the proposed C-type filter will be verifiedby the results of field tests in this section. The field datashown in Fig. 16 show the switching of the damping resistorRTS by back-to-back connected thyristor switches during LFtransformer energization. The control system sends a triggeringcommand to static switches whenever the instantaneous valueof current in RD = 250 Ω tends to exceed a prespecifiedthreshold value (10 A). This introduces a time delay of nearlya few half-cycles to the triggering instant of thyristors withrespect to the time instant of LF transformer energization.

The response of the proposed C-type filter is shown in Fig. 17(Case i). The response of the lightly damped conventionaldesign is also given in the same figure for comparison purposes(Case ii). As can be understood from the waveforms in Fig. 17,


Fig. 18. Harmonic and interharmonic analysis for field data after installationof the proposed filter. a) Single-line frequency components. (b) 2nd harmonic.(c) 1st interharmonic.

the new design approach significantly reduces the stresses onthe filter elements. Also, the 2nd harmonic subgroup in thefilter current is reduced more than 50% in comparison with thelightly damped conventional design.

Sample field data about single line harmonics, 2nd harmonicgroup and subgroup, and 1st interharmonic group and subgroupreflected into the supply after connecting the proposed C-type2nd HF are as shown in Fig. 18.

In the design of the new C-type 2nd HF, a comparativeevaluation has been made between filtering performances of theconventional and new design approaches for the same operatingconditions. The main assumptions in specifying the operatingconditions are as follows:

1) current harmonics produced by the TCR are notconsidered;

2) the voltage and current harmonics existing in the inter-connected system are ignored.

However, a TCR in an EAF application operates in a highlydynamic state resulting in unsymmetrical consecutive positiveand negative half cycles in its line current waveforms. This

TABLE ICOST COMPARISON (FILTER REACTORS, CIRCUIT BREAKERS,

INSTRUMENT TRANSFORMERS FOR RD , CABLES, AND LABOR COSTS

ARE EXCLUDED, AND UNIT PRICE OF ELECTRICITY IS 0.07 EUROS/kWh)

means that the even harmonic content of TCR line currentswill be rich and a considerable portion of the dominant 2ndharmonic component will close its path through the C-type 2ndHF.

The point of common coupling for the power system of LFsand other industrial loads is a 154-kV bus. Current harmonicscirculating in the interconnected system and voltage harmonicsat the 154-kV bus may cause an extra loading on the 2ndHF. Their combined effects on the C-type 2nd HF dependon the phase differences between furnace, TCR, and intercon-nected system harmonics. Therefore, as expected, field datashow higher harmonic and interharmonic contents (Fig. 18) incomparison with theoretical data shown in Fig. 14 (vi). A 95-Hzsingle-line harmonic value is an exception.


Fig. 19. Harmonic and interharmonic definitions as given in [13].

Fig. 20. Filtering performance of type 1. (a) Type 1. (b) Shunt HF currenttransfer characteristics. (c) Harmonics and interharmonics produced by EAF(Ieafn) and harmonics and interharmonics reflected to the supply after com-pensation (Isn).

A cost comparison is also made between the new and con-ventional design approaches. The results of the cost comparisonstudy are given in Table I. In this study, the following are true:


1) interest rate is neglected; 2) initial costs of filter reactors,circuit breakers, instrument transformers for RD, cables, andlabor costs are neglected, since they are the same for bothdesigns; 3) two identical EAFs having the same transformerratings are considered instead of two existing LFs; 4) harmonicsproduced by EAF are assumed to be two times bigger thanthose of equivalent LF, on the average; and 5) unit electricityprice is assumed to be 0.07 euros/kWh. Payback periods forthe proposed C-type 2nd HF are calculated by consideringbreakeven points in the cost analysis and are found as 1.31 and1.94 years when compared with conventional designs of mod-erate and high damping, respectively. These analyses includealso running costs arising from power dissipation on dampingresistors in both transient and normal operation states.

The results in Table I show the economic feasibility of theproposed system. Payback periods for the sample application



would be more than those of the EAF case given in Table I.Furthermore, the proposed C-type 2nd HF is technically feasi-ble because thyristorized static switches provide theoreticallyinfinitely many switchings for RTS.

V. CONCLUSION

The conventional design approach is a compromise betweentransient overvoltage suppression and steady-state filtering per-formance. However, the proposed C-type 2nd HF configurationcan meet both objectives simultaneously. This is achieved byintroducing a high electrical damping during LF transformerenergization and HF connection and a low electrical dampingduring normal operation of EAFs and LFs. Its effects in thesuppression of transient overvoltages are prominent. However,the attenuations in a single-line frequency of 100 Hz and 2nd

harmonic subgroup are marginal, but they are never amplifiedin contrary to the filtering performance of conventional designs.Furthermore, the proposed scheme reduces damping resistorlosses significantly on the annual basis. In the applicationswhere the number of transformer energizations is much lowerthan that of the sample system, conventional circuit breakersinstead of solid-state switches can also be used to connect anddisconnect the switched damping resistor RTS.

APPENDIX A

See Fig. 19.

APPENDIX B

The gray-colored harmonic and interharmonic spectra in thesupply lines in Figs. 20–22 also include components sinked bythe filters from the supply side and unfiltered part of the TCRharmonics. The magnitudes of harmonics and interharmonics insupply lines depend on the phase relationship between contribu-tions of supply, TCR, and furnace harmonic and interharmoniccomponents.

ACKNOWLEDGMENT

The Static Var Compensator project including the New C-Type 2nd Harmonic Filter was supported by ERDEMIR Ironand Steel Company.

REFERENCES

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Cem Özgür Gerçek (S’04) received the B.Sc. andM.Sc. degrees in electrical and electronics engi-neering from the Middle East Technical University,Ankara, Turkey, in 2004 and 2007, respectively,where he is currently working toward the Ph.D.degree in T-STATCOM control.

He is currently a Senior Researcher with the PowerElectronics Department, TÜBITAK UZAY ResearchInstitute, The Scientific and Technological ResearchCouncil of Turkey, Ankara. His areas of researchinclude reactive power compensation systems and

power quality issues.

Muammer Ermis (M’99) received the B.Sc. degreein electrical engineering from the Middle East Tech-nical University (METU), Ankara, Turkey, in 1972,the M.B.A. degree in production management fromAnkara Academy of Economics and CommercialSciences, Ankara, in 1974, and the M.Sc. and Ph.D.degrees in electrical engineering from METU in1976 and 1982, respectively.

He is currently a Professor of electrical engineer-ing with METU. His current research interest iselectric power quality.

Dr. Ermis was the recipient of the “The Overseas Premium” paper awardfrom the Institution of Electrical Engineers, U.K., in 1992 and the 2000Committee Prize Paper Award from the Power Systems Engineering Committeeof the IEEE Industry Applications Society. He was also the recipient of the 2003IEEE PES Chapter Outstanding Engineer Award and the “Outstanding PaperAward” from the Metal Industry Committee of the IEEE Industry ApplicationsSociety in 2009.

Arif Ertas (M’99) received the B.Sc. and M.Sc.degrees in electrical engineering from the MiddleEast Technical University (METU), Ankara, Turkey,in 1968 and 1969, respectively, and the Ph.D. de-gree in electrical engineering from The Universityof Manchester Institute of Science and Technology,Manchester, U.K., in 1973.

He is currently a Professor of electrical engineer-ing with METU. His current research interest iselectric power systems.

Kemal Nadir Köse received the B.Sc. degree inelectrical and electronics engineering from the Mid-dle East Technical University, Ankara, Turkey, in1993 and the M.Sc. degree from Hacettepe Univer-sity, Ankara, in 2001.

He was a Chief Senior Researcher with the PowerElectronics Department, TÜBITAK UZAY ResearchInstitute, The Scientific and Technological ResearchCouncil of Turkey, Ankara. He is currently an Elec-trical Engineer in Perth, Australia.

Özgür Ünsar (S’07) received the B.Sc. degree inelectrical engineering from the Middle East Tech-nical University (METU), Ankara, Turkey, in 2006and the M.Sc. degree in electronics engineering fromHacettepe University, Ankara, in 2010, where he iscurrently working toward the Ph.D. degree.

From 2006 to 2009, he was with the TurkishElectricity Transmission Company, Inc. (TEIAS). Heis currently with the Power Electronics Department,TÜBITAK UZAY Research Institute, The Scien-tific and Technological Research Council of Turkey,

Ankara, where he is a Researcher. His current areas of research include powerquality measurement and analysis.

Mr. Ünsar was the recipient of the “Outstanding Paper Award” from theMetal Industry Committee of the IEEE Industry Applications Society in 2009.

97 c-type 2nd harmonic filter

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