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IEEE TRANSACTIONS ON POWER DELIVERY 1

Impact of UPFC on Power Swing Characteristic andDistance Relay Behavior

Z. Moravej, Senior Member, IEEE, M. Pazoki, and M. Khederzadeh, Senior Member, IEEE

Abstract—This paper analyzes the distance relay performanceduring power swing conditions for an uncompensated and com-pensated transmission line with a unified power-flow controller(UPFC). UPFC can control voltage and power flow of the trans-mission line independently; hence, it has an impact on the apparentimpedance seen by the distance relay. To analyze the case, the ap-parent impedance seen by the distance relay during a power swingis extracted, and the results are synopsized graphically. The im-pact of UPFC on different transmission-line parameters from animpedance point of view is investigated. Moreover, the impact ofdifferent operation modes of UPFC and their reference values onthe apparent impedance seen by concentric circles as a powerswing detection method are also evaluated by detailed simulations.

Index Terms—Distance relay, power swing, static compensator(STATCOM), static synchronous series compensator (SSSC), uni-fied power-flow controller (UPFC).

I. INTRODUCTION

T HESE DAYS, more than ever, advanced power-electronicequipment technologies or flexible ac transmission sys-

tems (FACTS) are paramount for more efficient utilization andcontrol of existing transmission networks. The new generationof FACTS controllers with self-commutated voltage-sourceconverters (VSCs) are similar to an ideal rotating synchronousmachine with instantaneous response, no inertia, controllableamplitude, and phase angle [1]–[3]. They do not significantlyalter the existing line impedance, but they can internally gen-erate or absorb reactive power. Furthermore, some devices,such as a unified power-flow controller (UPFC) can exchangereal power with the ac system. However, the reaction of FACTScontrollers during different system conditions, such as faultsor power swings, has an adverse effect on the operation ofdistance relays as the positive-sequence impedance measuredby traditional distance relays is no longer an indicator of thedistance to a fault [4], [5].UPFC consists of series and shunt VSCs with a common dc

link. The function of the shunt converter is to supply or absorbthe real power demanded by the series converter at the commondc link. Moreover, it can also generate or absorb controllable

Manuscript received February 07, 2013; revisedMay 15, 2013; accepted June19, 2013. Paper no. TPWRD-00171-2013.Z. Moravej and M. Pazoki are with the Electrical and Computer Engi-

neering Faculty, Semnan University, Semnan 3519645399, Iran (e-mail:[email protected]; [email protected]).M. Khederzadeh is with the Department of Electrical Engineering, Power

and Water University of Technology (PWUT), Tehran 165895371, Iran (e-mail:[email protected]).Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TPWRD.2013.2270408

reactive power for voltage regulation. The function of the seriesconverter is to supply or absorb the required reactive power lo-cally. It also exchanges active power as a consequence of thecontrollable injection ac voltage in series with the transmissionline via a series transformer [1], [2]. Therefore, a UPFC can reg-ulate the bus voltage and active/reactive power independentlyand simultaneously lead to uncertain apparent impedance mea-suring by the distance relay during a fault or even power swings.The impact of UPFC on the operation of protective relays

is analyzed in the literature. In [6], the effect of UPFC on dis-tance relay is simulated for different fault locations. In [7], thedistance relay tripping characteristic in the presence of UPFCis obtained and a modified distance protection scheme is pro-posed. The work in [8], evaluates a distance relay performancein a compensated line with UPFC for different fault conditions.In [9], the impact of series and shunt compensating parts of aUPFC on the distance relay is analyzed individually and col-lectively. In [5] and [10], the impacts of VSC-based multilineFACTS controllers and STATCOM modeling on the distancerelay are investigated analytically and by detailed simulationsfor different fault conditions, respectively.Although many researchers considered the distance relay

performance for different fault types with various FACTSdevices, very few publications are available considering thedistance relay performance for a compensated line during apower swing condition. In [11], it is shown that the impedanceseen by distance relays at the sending and receiving end termi-nals of the transmission line are circles during power swings.The authors in [12] simulated and compared the performanceof two power swing detection algorithms with and withoutseries capacitors.The aim of this paper is to analyze the impedance seen by a

distance relay during power swing conditions in a compensatedline with UPFC using analytical and simulation methods. Themain contributions of the paper are as follows.• An analytical comparison between an uncompensatedand compensated line with UPFC during a power swingcondition is presented analytically by extracting apparentimpedance equations and graphically by impedancediagrams.

• The impact of UPFC on the line constants (ABCD) from animpedance point of view is analyzed. The UPFC practicalconstraint to provide the active power needed by the seriesconverter by using a shunt converter via a common dc linkis also considered.

• The impedance locus corresponding to a new -model ofa UPFC-embedded line during the power swing conditionis presented.

0885-8977/$31.00 © 2013 IEEE


2 IEEE TRANSACTIONS ON POWER DELIVERY

Fig. 1. (a) Equivalent UPFC-embedded line where, and . (b) Equivalent

power injection -model.

• The impedance seen by the distance relay during a powerswing utilizing full detailed modeling of the UPFC-em-bedded line is simulated. The impact of the dynamic re-sponse of UPFC, reference values of the controllers, andoperation modes of UPFC on the impedance locus are alsoinvestigated.

• The impact of different operation modes of a UPFC andtheir reference values on the concentric characteristicscheme are considered [13]. The elapsed time required bythe impedance locus to traverse between two impedancecharacteristics is evaluated for different conditions.

The apparent impedance analysis during the power swingis described in Section II. The sample system is presented inSection III. The simulation results and discussions are presentedin Section IV. This paper concludes in Section V.

II. APPARENT IMPEDANCE ANALYSISDURING THE POWER SWING

In this section, a general equation for sending and receivingend impedances seen by the relays during the power swing isextracted based on the line constants (ABCD), UPFC compo-nents, and the sending/receiving terminals voltage. As shown inFig. 1(a), UPFC is inserted at the beginning of the line. The ap-parent impedance seen by the relay is analyzed at busesand for uncompensated and compensated lines, respec-tively.

A. Transmission Line Without a Compensator

The sending power at bus is , whereas and arerelated by the line constants matrix. Consequently, the sendingend apparent impedance seen by the distance relay at bus canbe calculated by . Therefore, , in termsof line constants and terminal voltages, can be derived as [6]

(1)

where is a function of the power angle . Generally, in thispaper, , and are the line constants;

and stand for voltage and current at bus ,and ); and the bold symbols are the complex values. More de-tails regarding (1) are described in [6].Similarly, the equation of the apparent impedance seen by the

relay at the receiving end terminal (at bus ) can be derived.When (1) is plotted on the R-X diagram, it is portrayed by

a family of circles, as depicted in Fig. 2. The derivation of

Fig. 2. Construction of the sending end impedance locus (with/without UPFC).

impedance circles based on power-angle variation between0–360 , as shown in Fig. 2, has the following significant notes[6]:• In the case of and , the centersof circular characteristics lie below and above the origin ofthe R-X diagram, for example, and , respectively.In the case of , the circle radius is andit seems to be a straight line. In the case of a short circuitat the relay location and far end of the line, the impedanceloci change from a circle to a point which coincide withorigin and , respectively. Therefore, the far end ofthe protected line is identified at , whereas the origincan likewise be named near the end of the protected line.

• In Fig. 2, circles corresponding to 0.1 p.u.are plotted. Prior to system disturbances, in normal systemoperation, the power angle is relatively small (between0 –30 ). At this moment, the direction of the power flowis from bus to the line at the relay location. In the powerswing condition, terminal voltages will have drifted apartby several degrees. Therefore, the sending impedance seenby the relay has moved around circular characteristics fromthe normal position (small power angle) toward the tripzone of the relay. In Fig. 2, it can be seen that by increasingthe power angle, as it exceeds 90 , the resulting imped-ances have smaller values. The recovery of the system tonormal operation causes the impedance to retrace the path(between 0 –90 ) until the system operates at a new powerangle. It is worth noting that the out-of-step circumstancedevelops the circular characteristic of the impedance locus.For opposite direction of power flow, a similar analysis canbe performed.

B. Transmission Line With UPFC

Fig. 1(a) represents an equivalent UPFC-embedded line. TheUPFC is inserted between buses and in the line. The config-


MORAVEJ et al.: IMPACT OF UPFC ON POWER SWING CHARACTERISTIC AND DISTANCE RELAY BEHAVIOR 3

uration consists of the line -model and the steady-state modelof UPFC. The series and shunt converters are modeled by twocomplex voltages (series with impedance ) and

(series with admittance ), respectively.The -model of the combination of line and UPFC will be

extracted based on complex voltages and currents at buses( , and ). From the circuit of Fig. 1(a), (2)can be derived as [15]

(2)

Let , then and in admittance matrix (Y ma-trix) can be decomposed into two components, that is,

and . Consequently, the UPFC-em-bedded line can be modeled by the equivalent power injection-model, as shown in Fig. 1(b). In this figure, and standfor complex power flowing out of buses in the line, andand are complex power injection due to the shunt andseries parts of UPFC, respectively.With the goal of apparent impedance calculation during a

power swing, a general formula for sending end impedance, ac-cording to the circuit of Fig. 1(b), can be derived. The sendingpower at bus can be written by using (2) as follows:

(3)

where

(4)

The impedance seen by the relay location at bus is. During power-angle variation between 0–360 , it is

expressed as

(5)

where and are identified in (2) and (4), respectively,and is a function of the power angle . Moreinformation about (5) is available as follows.• Generally, the angular position of the generated ac outputvoltage by the shunt converter is controllable with respectto the ac system voltage. So the shunt controller providesthe active power demand of the series converter by regu-lating the dc-link voltage. The aforementioned constraintshould be considered in power calculations. The activepower delivered to the shunt converter is ,where is a drawn current by the shunt part, as shown inFig. 1(a). On the other hand, the active power demandedby the series converter is , whereas it

must be equal to . Therefore, as the output voltageangle of the shunt converter can be calculated.

• The first and second components of (5) give the centerand radius of the circular characteristic, respectively. It canbe seen that all of the series voltage , series impedance, shunt voltage , and shunt admittance have direct

impacts on the center and radius of the power swing circle.The direct effect of the mentioned parameters appears in

.• The impedance locus of the UPFC-embedded line duringthe power swing condition corresponding to voltage ratios

, and 0.9 (similar to uncompensatedsystem) are plotted in Fig. 2, where , and arethe center of the circles, respectively. It can be seen thatUPFC directly affects the radius and center of impedancecircles. In the case of the power angle 0 , the directionof the power flow due to the UPFC phase shift is fromthe line to the bus. Similar to the uncompensated line, astep-by-step analysis of the power-angle behavior duringpower swing conditions can be concluded from Fig. 2.

According to (5), the impacts of line constants, UPFC com-ponents (while considering the link between series and shuntparts), and two end voltages on the sending impedance seen bythe relay during the power swing are clarified. Similarly, a gen-eral formula for receiving end impedance seen by the relay atbus can be derived as

(6)

where .

C. UPFC Impact on Transmission-Line Constants

In this section, it is desirable to obtain new con-stants for the UPFC-embedded line. Therefore, based on newconstants, the new representative -model can be concluded.For a numeric example, will be calculated, where

0.4 p.u. , and 1.4 p.u.( is calculated from the constraint of .) The newconstants calculation procedure is described as follows.

constant: it can be seen from (1), according to the con-dition , that the impedance circle seems to bea straight line. With respect to the mentioned point, when (5)is equated to (1), the same result can be deduced. From (5),when the impedance equation denominator is equal to zero, theimpedance seen by the relay will be . This condition can befound as an open-circuit case at the relay location (bus ). For theknown value of , the magnitude of the receiving end voltagecan be calculated by using (4) and (5) as follows:

(7)

Compared to the same condition of the line without UPFC,the obtained new ratio of , from (7), is equivalent tothe new constant of the UPFC-embedded line. It can be seenfrom (7), corresponding to the different series and shunt com-pensation levels, that the range of will be determined.



Fig. 3. Construction of the sending-end impedance circle diagram using (5).

Fig. 4. Variation of the angle with respect to the power angle .

General circuit constants used in the analytical and simulationsections are given in the Appendix. From the numeric example,when 1 p.u., is obtained as 0.5806. By plotting thecircle, as shown in Fig. 3, it is found that the circle has a radiusof . Therefore, from an impedance point of view, one of thenew -model constants is calculated.It can be derived that and are related by a curve for the

numeric example, as shown in Fig. 4.constant: according to (1), when 0 (short cir-

cuit at the end of line), the impedance locus is a point on. From (5), for a given power angle and

, the impedance locus is in thecase of a compensated line. It can be expressed as follows:

(8)

Accordingly, can be calculated for different compensationlevels of UPFC. Based on the same compensation and system

conditions, first, the constant of the new -model can be ob-tained. Second, can be determined. Consequently, accordingto (8), the constant is identified.From the numeric example, is equal to .

Since the constant was calculated, therefore, the con-stant is . Generally, the angle of is relativelysmall. Hence, the constant angle can be assumed approxi-mately to zero and the constant angle will be subsequentlyachieved.

constant: For a uniform symmetrical line, but in a nonuniform line, they are not equal. In the

latter case, the new constant is calculated from the re-ceiving-end impedance. As a special case, where ,the impedance circle can be plotted in the R-X diagram. Inthis case, the circle radius is and it seems to be a straightline. Accordingly, by a similar calculation procedure for theconstant, can be attained. For the known value of , themagnitude of the sending terminal voltage can be calculatedusing (6) as follows:

(9)

From (9), the obtained new ratio of is equivalent tothe constant of the UPFC-embedded line. From the numericexample, is equal to 0.905.

constant: the determinant of the line constants matrix isone or close to one. Therefore, can be approximated ac-cording to three obtained constants. From the numeric example,

is calculated.As a consequence of the calculation, the new-model of the UPFC-embedded line is derived. Moreover,from an impedance point of view, the impact of UPFC on theoriginal constants of the line is extracted.The sending-end impedance loci based on the obtained gen-

eral formula for the UPFC-embedded line can be portrayed. Thenew -model of the system helps the graphical representationof the sending-end impedance seen by the relay (bus ) for thecompensated line with UPFC.As shown in Fig. 3, five particular conditions are investigated

in (5), that is, and :• A short circuit at the relay location causes the near end ofthe line to be located at .

• In the case of , the centers of circular char-acteristics are below the R-X diagram, for example .

• In steady-state system operation, it is not practical that theratio has a value as low as magnitude. But it isuseful for the demonstration of the UPFC effect on systemparameters, especially impedance seen by the relays.When

, it is an open-circuit condition at the relaylocation. Therefore, the impedance circle radius is .

• In the case of , the centers of this group ofcircles are located above the origin of the R-X diagram, forexample, .

• The circles of the last case are obtained when 0. Sim-ilar to the uncompensated line, corresponding to a short-circuit condition at the far end (bus ), the impedance locusduring the power swing can be obtained. This characteristic



Fig. 5. Construction of the receiving-end impedance circle diagram using (6).

Fig. 6. Sample system.

for an uncompensated line is a point which is located at ,as shown in Fig. 2. Meanwhile, due to the presence of theseries and shunt compensation, the far end of the compen-sated line is a circular locus in the power swing condition.

From Fig. 3, the dynamic behavior of the impedance seen bythe relay during the out-of-step condition can be deduced.Whenthe power angle is zero, by referring to the compensation ef-fect of UPFC, the direction of power flow is from the line tothe bus at the relay location. In normal system operation, theangle is relatively small (10 –30 ) and the impedance locusis lying in the load region. Whenever a short circuit occurs atthe line, by the correct action of relay and breakers, bus voltageswill drift apart by several degrees as mentioned for the uncom-pensated line. A similar analysis of receiving-end impedancecan be represented in Fig. 5.

III. SAMPLE SYSTEM

The sample system used for simulation is in Fig. 6 [17]. Threegenerators and their hydraulic turbines, governors, excitationsystems, distributed line, and loads are simulated with detailedrepresentation of components in the MATLAB/Simulink envi-ronment using the SimPowerSystems toolbox [14]. The relevantdata for the sample system are given in the Appendix.

A. UPFC Control

From a functionally standpoint, the UPFC is a very versatilepiece of equipment. The series and shunt parts of the UPFC en-able it to operate in several operation modes. The generic struc-

ture of the UPFC consists of two converters: one connected inshunt and the other in series with the line, both connected bya common dc link, as shown in Fig. 6. Such a configurationprovides voltage and active/reactive power flow control for thepower system [2].In the automatic voltage-control system of STATCOM, as a

shunt part of UPFC, the three-phase current, which will be deliv-ered to the line, is transformed into reactive and real currentcomponents. The reactive/active current references aregenerated by feeding an ac/dc bus error voltage to two differentcontrollers. These current references are compared with the cor-responding parts of the decomposed shunt current. Then, theobtained error signals are fed to another controller to calculatemagnitude and angle of the shunt converter. Moreover, in theshunt controller, a limiter prevents the shunt converter referencecurrent from exceeding its maximum rated value.The automatic power-flow control in the control system of

SSSC, as a series part of UPFC, is achieved. The desired realand reactive current components are calculated correspondingto and . Then, they are compared with the decom-posed measured line currents and fed to a controller to derivethe magnitude and angle of the series converter voltage. The se-ries-injected voltage limiter of the SSSC controller takes prac-tical limits on series voltage into account [3]. Moreover, SSSCcan operate in the manual injection voltage mode where directvoltage injection based on the selection of through the se-ries coupling transformer is possible [16].

IV. SIMULATION RESULTS

From Fig. 6, the distance relay R is located at bus B4 (line 1).For accurate modeling of the conventional distance relay, thefollowing procedure is applied: digital waveforms are createdby using sampling rate of 96 kHz, and they are digitally filteredby using a second-order Butterworth low-pass filter with acutoff frequency of 240 Hz, downsampled to 16 sample/cycle,and processed with full-cycle discrete Fourier transform(FCDFT) to estimate the phasor value of the fundamental [10],[18]. Moreover, a digital mimic filter is used to remove dc offset[19]. UPFC is installed at the beginning of line 1. The impactof different functions (UPFC, STATCOM, and SSSC) on theimpedance seen by the distance relay during the power swingis analyzed. After the occurrence of a power swing, the powerflows and bus voltages change. Therefore, the series and shuntcontrollers respond to a variation of system parameters. Ac-cordingly, FACTS controllers affect the impedance locus shapeform and the speed of the impedance trajectory movement.

A. UPFC Influence on Impedance During the Power Swing

For power swing simulation, a fault occurs at 1 s on the endof line 3 and is cleared by opening breakers at buses 1 and7 (corresponding to line 3 in Fig. 6). For investigation of theUPFC effect on the impedance locus during the power swing,the reference values of UPFC must be adjusted. Referencesare of the line belonging to the series converter andvoltage value of the shunt converter.Fig. 7 shows the impedance locus seen by relay R in the

sample system of Fig. 6 during the power swing with andwithout UPFC. The reference values of UPFC are fixed at



Fig. 7. Sending impedance seen by the relay without and with the UPFC.

932 MW, 66 MVAr, and 0.9749 p.u. Thepower flows and bus voltage are equal in values for the systemwith and without compensation devices. It can be seen that theimpedance circle corresponding to the compensated line hasdifferent centers and radiuses from an uncompensated line asshown in (5). Also, the relay voltage and current, magnitudeof injected series voltage, and drawn shunt current duringthe power swing are shown in Fig. 8. From (5), along withFigs. 3 and 7, it can be deduced that the impedance circle shapeduring the power swing is changed for the compensated line. Inthe simulation model, the bus voltages vary within the powerswing continuously. Thus, the obtained impedance locus differsfrom equation-based plots. In order to determine the impactof individually, at a constant value of , two valuesof within permissible limits are selected. Similarly, forthe individual determination of the impact, at a constantvalue of , two values of within permissible limits areconsidered. Fig. 7 shows that the impedance circles are thesame for two different values of and during the powerswing condition.

B. STATCOM Influence on Impedance During the PowerSwing

When the UPFC operates on STATCOM mode, the shuntconverter effect can be analyzed individually. In Fig. 9, threegeneral impedance loci corresponding to three are con-structed. Whenever the power swing condition occurs, the busvoltage is changed. Hence, the associated shunt controller at-tempts to bring it to the reference value. STATCOM can providecapacitive or inductive output current independent of the systemvoltage. In voltage regulationmode, STATCOM (with respect toreference voltage) absorbs or generates reactive power at the in-stallation point. It can be seen from Fig. 9, three reference valuesof STATCOM increase the impedance circle radius during thepower swing due to shunt controller response as shown in (5).It is worth noting that in the UPFC operation mode, the shuntpart of the UPFC has to supply the reactive power required by

Fig. 8. (a) Relay voltage., (b) Relay current. (c) Magnitude of injected seriesvoltage. (d) Magnitude of drawn shunt current.

Fig. 9. Sending impedance seen by the relay with STATCOM.

power system control, while maintaining the exchange of thereal power required by the series part [2]. Therefore, the ef-fect of series and shunt voltages determines the radius of theimpedance.

C. SSSC Influence on Impedance During the Power Swing

The UPFC device can be employed in SSSC mode. SSSCcontrols the effective line impedance. It injects a controllablecompensating voltage in quadrature with the line current to em-ulate capacitive or inductive compen-sation modes [16]. SSSC can provide line voltage regulationwith control of the effective line impedance. With direct in-jection of the required compensating voltage, SSSC attemptssystem recovery in the power swing condition with respect toits operation mode. Consequently, the series voltage injectioncan affect the impedance locus during the power swing. It can



Fig. 10. Sending impedance seen by the relay with SSSC.

be concluded from Fig. 10 that the impedance locus changesslightly, when 0. In inductive mode, the impedancelocus during the power swing has a greater radius in compar-ison with the obtained one in the capacitive mode. In addition,the impedance locus seen by the relay through the capacitivemode has a smaller radius compared with the case of an uncom-pensated system.

D. UPFC Influence on Power Swing Blocking Scheme

The conventional power swing blocking (PSB) scheme oftenutilizes the concentric characteristic method [4]. In the PSBscheme, the outer characteristic is an offset char-acteristic which is concentric with the third zone of thedistance relay. During the power swing, the impedance locustraverses from the to the slower than a fault condition.Therefore, the major effort is to set the timer of the PSB scheme.To find the correct setting for the PSB time delay, extensive sta-bility studies are typically required.In this paper, the impact of UPFC, STATCOM, and SSSC

on the time taken of the impedance locus to traverse betweenand is investigated, as shown in zoomed sections of

Figs. 7, 9, and 10. Table I depicts the output of the PSB schemetimer which started counting when the impedance locus lies be-tween and . This measurement is performed for an un-compensated system and three operation modes of UPFC withdifferent reference values. In a simulated system of Fig. 6, theclearance of a fault at the end of line 3 causes a power swingand then the timer output is recorded. From Table I, three oper-ation modes of the UPFC can be extracted, causing an increaseof the impedance trajectory movement speed. Moreover, it canbe seen that in the presence of SSSC, the impedance movementhas the highest rate. In addition, a less and greater effect on thetimer measurement is related to STATCOM 0.97) andSSSC 0.05), respectively. Due to the SSSC improve-ment effect on system stability, fault duration requires 18 cyclesfor power swing occurrence.

TABLE IOUTPUT OF THE DISTANCE RELAY TIMER DURING THE POWER SWING

TABLE IISAMPLE SYSTEM DATA

V. CONCLUSION

In this paper, the impact of UPFC on the power swing char-acteristic, line constants, and PSB scheme is investigated by an-alytical and simulation methods. The main achievements of thisstudy are summarized as follows.• An analytical and graphical analysis for the impedanceseen by the relay for the UPFC-embedded line during thepower swing is presented.

• From an impedance point of view, the impacts of UPFC onthe line constants are extracted.

• Based on the new -model of the UPFC-embedded line,the far end of the protected line is dependent on the com-pensation level of the UPFC.

• Detailed and accurate simulation of the compensatedsystem demonstrates the adverse effect of UPFC on the



radius and center of the impedance circle seen by the relayduring the power swing condition.

• Different reference values of UPFC have no remarkableimpact on the impedance locus during the power swing.

• In STATCOM operation mode, the radius of the impedancecircle is increased in comparison with the uncompensatedsystem.

• In SSSC operation mode, the radius of the impedance locusis increased (in inductive mode) and decreased (in capaci-tive mode), compared to the uncompensated system.

• Three operation modes of the UPFC increase the speedof the impedance trajectory movement. Hence, in orderto find the fastest power swing for the timer setting, com-prehensive stability studies on the compensated system arerequired.

APPENDIX

A list of some sample system parameters are given in Table II.

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Z. Moravej (SM’11) received the B.E and M.E de-grees in electrical engineering from Bangalore Uni-versity, India, in 1985 and 1991, respectively, and thePh.D. degree from Banaras Hindu University, India,in 2001.Currently, she is an Associate Professor with

the Electrical and Computer Engineering Faculty,Semnan University, Semnan, Iran. Her areas ofresearch interest include the application of artificialintelligence and machine learning in power systemprotection, power-quality monitoring, and substation

automation systems.Dr. Moravej is a member of CIGRE and a member of IAEEE of Iran.

M. Pazoki received the B.Sc. and M.Sc. degreesin electrical engineering from Semnan University,Semnan, Iran, in 2008 and 2010, respectively, wherehe is currently pursuing the Ph.D. degree.His research interests include power system pro-

tection, flexible ac transmission systems devices, andpower-quality monitoring.

M.Khederzadeh (SM’06) received the B.Sc. degreein electrical engineering from Sharif University ofTechnology, Tehran, Iran, in 1980, the M.Sc. degreein electrical engineering from Tehran University,Tehran, Iran, in 1990, and the Ph.D. degree inelectrical engineering from Sharif University ofTechnology in 1996.He was a Postdoctoral Fellow with the University

ofWestern Ontario, London, ON, Canada, from 2004to 2005. Currently, he is an Associate Professor andDirector of the Power System Protection and Control

Research Center, Electrical Engineering Department, Power and Water Univer-sity of Technology, Tehran. His research interests include power system protec-tion, control and monitoring, and power system dynamics.Dr. Khederzadeh is a member of the Institute of Engineering and Technology

and CIGRE.

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IEEE TRANSACTIONS ON POWER DELIVERY 1 Impact of UPFC on Power Swing Characteristic …electricaltranslate.ir/wp-content/uploads/2016/03/Impact... · · 2016-10-10FACTS controllers