1902 ieee transactions on power delivery, vol. 26, no. 3,...

1902 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 26, NO. 3, JULY 2011

A New Technique to Detect Faults in De-EnergizedDistribution Feeders—Part II: Symmetrical

Fault DetectionXun Long, Student Member, IEEE, Yun Wei Li, Member, IEEE, Wilsun Xu, Fellow, IEEE, and

Chris Lerohl, Student Member, IEEE

Abstract—To ensure safe re-energizing of an overhead distribu-tion feeder after it is de-energized for an extended period, a novelfault detection technique by controlling a thyristor-based deviceis proposed in a companion paper. The device connected in par-allel with a breaker or recloser can inject electrical pulses with ad-justable strength for the downstream fault detection in a de-en-ergized system. The proposed method can effectively detect dif-ferent kinds of asymmetrical faults based on the unbalanced faultcurrents. However, the unbalanced current-based fault detectionscheme is not effective for three-phase symmetrical faults detec-tion. Furthermore, a stalled motor or a shunt-connected capac-itor bank in the downstream may also behaves like a short-circuit.Therefore, a fault detection algorithm based on the analysis of theharmonic impedance of the de-energized system is developed inthis paper. This method is very effective for the symmetrical faultdetection and for distinguishing a stalled motor and capacitor bankfrom a fault. Extensive lab test results are provided in the paper toverify the effectiveness of the proposed method.

Index Terms—De-energized distribution line, fault classification,fault detection, power electronics, safe recloser.

I. INTRODUCTION

A FTER an overhead distribution feeder is de-energized foran extended period due to events, such as repair, mainte-

nance, or storms, there is always the possibility that humans oranimals may be in contact with feeder conductors unknowingly[1], [2]. A re-closing action in such a situation can easily leadto fatality [3], [4]. For this reason, re-energizing a de-energizeddistribution feeder in a safe manner is a major consideration forutility companies [5]–[9]. Therefore, the development of tech-niques that can detect whether the downstream system is stillexperiencing a fault before restoring the de-energized systemis important, so that operators can re-energize the feeder withconfidence.

The fault detection in de-energized systems is challengingsince it requires the generation and injection of a voltage signalto the de-energized feeder. Available techniques for this signalgeneration are either self-powered which is based on battery/ca-

Manuscript received October 03, 2010; revised January 07, 2011; acceptedFebruary 08, 2011. Date of publication April 05, 2011; date of current versionJune 24, 2011. This work was supported by the iCORE . Paper no. TPWRD-00759-2010.

The authors are with the Department of Electrical and Computer Engineering,University of Alberta, Edmonton, AB T6G 2V4 Canada (e-mail: [email protected]; [email protected]; [email protected]; [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/TPWRD.2011.2118238

pacitor [10], [11] or by using energy from the upstream [12],[13]. A pulse-recloser technique in [14] can reduce a large in-rush current; however, it is hard to distinguish a fault from astalled motor or a shunt capacitor bank, which behaves like ashort circuit. Moreover, all of the available methods cannot pro-duce a signal with adjustable and enough strength that can beused for high-impedance fault detection. Also, these methodscannot detect all types of faults in a single device.

Considering the limitations of the existing fault detectionmethods, a new technique based on a thyristor bridge in parallelwith the breaker or recloser was proposed in a companionpaper [15]. In the proposed method, a controllable signal isinjected into the de-energized downstream to stimulate theelectrical response. With adjustable pulse strength by changingthe thyristor firing angle, a low-voltage pulse can be created tosatisfy the safety requirement and a high-voltage pulse can beproduced to break down an insulted gap of a high-impedancefault when necessary. The principle and key features of theproposed idea have been presented in that paper. Moreover, themethod and procedure for detecting asymmetrical faults basedon the unbalanced fault currents are also discussed.

This paper completes [15] by proposing a symmetrical faultdetection method and considering situations of downstreamstalled motors or shunt capacitor banks. Since a symmetricalfault affects all three phases equally, the method based onthe difference of three-phase currents for asymmetrical faultsdetection is not applicable here. Furthermore, when a voltagepulse is applied to the de-energized circuit, either a stalledmotor or a capacitor bank can cause a large current like a shortcircuit. Thus, it is necessary to explore a new fault detectionmethod that is not only based on the fault current magnitude.In this paper, a fault detection method is developed based onthe harmonic impedance characteristics. Combined with theasymmetrical fault detection algorithm developed in [15], adetection scheme that can detect all kinds of faults and candistinguish a fault from a stalled motor or a shunt capacitorbank is then proposed.

This paper is organized as follows. The new fault detec-tion criterion based on harmonic impedance is introduced inSection II. In this section, the harmonic impedance character-istics under different situations are first analyzed. Based onthe harmonic impedance characteristics, the proposed methodfor detecting a symmetrical fault and for distinguishing afault from a stalled motor or a capacitor bank is then devel-oped. Section III presents the lab test results obtained from a

0885-8977/$26.00 © 2011 IEEE

LONG et al.: NEW TECHNIQUE TO DETECT FAULTS IN DE-ENERGIZED DISTRIBUTION FEEDERS—PART II 1903

Fig. 1. Proposed scheme for symmetrical faults detection.

Fig. 2. Equivalent circuit with a symmetrical fault.

single-phase low-voltage system, which verifies the effective-ness of the proposed method. Finally, the work is summarizedin Section IV.

II. FAULT DETECTION BASED ON HARMONIC IMPEDANCE

As shown in Fig. 1, a zero-sequence voltage from one ener-gized phase is fed to all three phases when the thyristors T1,T3, and T5 are fired simultaneously on a certain degree beforethe voltage cross zero. The corresponding current pulse in eachphase depends on the line condition. In a normal condition, theinjected currents are very small. However, if there is a symmet-rical fault, inrush currents will show up in all phases at the sametime. To illustrate this, a representative 25 kV system with a10 km distribution line is used as shown in Fig. 2, where theparameters of the system are listed in Table I. To compare thedifference of the faulted and unfaulted conditions, a symmet-rical fault is created at 5 km away from the recloser. When thethyristors are fired at 150 , the transient voltage and the tran-sient current are shown in Fig. 3. Apparently, a symmetricalfault increases the current magnitude. However, this fault cur-rent magnitude highly depends on the fault resistance . Itis therefore difficult to set up an appropriate current magnitudethreshold to detect whether a fault exists, especially consideringthe possibility of a high-impedance fault.

Further considering the situations of stalled motors and shuntcapacitor banks connected at downstream, where a high cur-rent similar to a short circuit may be produced by the detectionvoltage , a fault detection method not just based on the cur-rent magnitude is required.

To meet this fault detection requirement, a new method basedon the harmonic impedance is introduced in this section. Theharmonic impedance can represent the frequency response ofpower networks. With its unique characteristics, the harmonicimpedance can be effectively used to detect a symmetrical fault.

TABLE IPARAMETERS OF A REPRESENTATIVE 25-kV SYSTEM

Fig. 3. Voltage �� and current �� in different conditions.

Fig. 4. Downstream de-energized lines as a linear network.

As will be shown later in this section, the harmonic impedancecan also be used to distinguish a stalled motor or a capacitorbank from a fault.

A. Study of Harmonic Impedance for Fault Detection

Considering the downstream de-energized line as a linear net-work (Fig. 4), an equation can be established according to theFourier transform of nonperiodical signals [16]

(1)

where are the Fourier transforms of transientvoltage and current, and is the harmonic impedance.

The harmonic impedance can therefore be expressed as

(2)


Fig. 5. Harmonic resistance �� in unfaulted and faulted cases.

Fig. 6. harmonic reactance �� in unfaulted and faulted cases.

or

(3)

where , and is the fundamental frequency (60 Hzis considered in this paper).

These equations imply that the harmonic impedance can bemeasured by using the DFT of transient voltage and current sig-nals. To implement this approach, the Fourier transforms of thecurrent and voltage are created using an FFT algorithm. Sepa-rating harmonic impedance into its resistance and reac-tance parts gives

(4)

The basic principle of the proposed idea is to utilize thechange of in different conditions to detect a symmetricalfault.

In normal conditions, the harmonic impedance of the de-en-ergized downstream as shown in Fig. 2 is

(5)

where are the equivalent resistance and inductanceof the load, (see Fig. 2). From (5), it can

be seen that the harmonic reactance is proportional to thefrequency, and the ratio is

(6)

However, if a symmetrical fault exists, the harmonicimpedance will become

(7)where is the fault resistance. Thus, the harmonic resistance

and harmonic reactance change to and

(8)

(9)

The harmonic resistance and reactance in the two condi-tions (faulted and unfaulted) are compared in Figs. 5 and 6,respectively.

Since is much smaller thanwhen the frequency is low, one can obtain

from (8) at low frequencies (such as 0 360 Hz).On the other hand, consists of two parts: the first part

is proportional to the frequency but the ratiobecomes much smaller as

(10)

And the second part of decreases with an increase infrequency. Thus, the overall effect of the harmonic reactanceis that is much smaller than and it almost has nosignificant change at low frequencies.

Based on the above analysis, harmonic impedance can be uti-lized for symmetrical fault detection. The decision logic is there-fore designed as follows.

1) Measure the currents and voltages of three phases after T1,T3, and T5 are fired simultaneously.

2) Are currents the same?If No, turn to asymmetrical faults analysis.If Yes, estimate the .

i) If is proportional to frequency, there is nofault.

ii) If has no significant change as frequencyincreases, there is a symmetrical fault.

B. Impact of Stalled Motor

A stalled motor behaves like a short circuit in the de-ener-gized system. The equivalent circuit of a stalled motor is shownin Fig. 7 [17]. The parameters and are the motor stator re-sistance and leakage reactance, and the locked-rotor resistanceand leakage reactance referring to the stator side are denoted as

and , respectively. The reactance is the magnetizingreactance of the motor. The stator current is , and the rotorcurrent is . The motor slip when the motor is stalled.


Fig. 7. Equivalent circuit of a stalled motor.

Fig. 8. stalled motor connected in the downstream system. (Note: the stalledmotor: 5000 hp, starting�� , inrush current 700%, fed with a three-phase5 MVA transformer, 25 kV/4.16 kV, � � 0.05).

Fig. 9. Effect of a motor on the current pulse.

Considering , the impedance of a stalled motor istherefore expressed as

(11)

Typically, the motor starting power factor is between 0.20.3, and the motor inrush current is 600% 800% of the ratedcurrent. Thus, a stalled motor in a de-energized line can cause alarge current pulse when a voltage is applied (Fig. 8). The cur-rents in different conditions are illustrated in Fig. 9, in whichthe current pulse with a stalled motor connected is comparableto the fault current. This also indicates that the current magni-tude is not a good indicator to distinguish a fault from a normalcondition with a stalled motor.

From the aspect of frequency domain, the impedance of astalled motor is more inductive, and then the resistance in(11) can be ignored in a simplified model. When a stalled motoris connected parallel to a load as shown in Fig. 8, the reactanceof the downstream becomes

Fig. 10. Harmonic reactance �� with a stalled motor.

Fig. 11. Shunt capacitor bank connected in the downstream. (Note: a three-phase capacitor bank, 2.5 MVar, Yg connected. Fed with a 5 MVA, 25 kV/0.6kV, Yg/Yg transformer � � �� .

(12)

where is the reactance of downstream with a stalledmotor, and is the inductance of a stalled motor. The firstpart of the is proportional to frequency and theratio ; the second part of the

increases with an increase in frequency. In this case,increases significantly as the frequency increases as

shown in Fig. 10. This scenario is clearly different from the re-actance in a faulted condition. Thus, similar to the detec-tion of symmetrical faults, versus frequency can be usedto distinguish a fault from a stalled motor.

Note that using the reactance versus frequency criterion caneffectively distinguish a fault from a stalled motor situation, butit cannot distinguish a stalled motor from a normal (no fault)condition as they both have a similar X/f ratio. However, de-tecting the existence of a stalled motor is not really the purposeof this paper. As long as a fault can be effectively detected, theproposed detection scheme can work properly.

C. Impact of the Capacitor Bank

As shown in Fig. 11, a shunt capacitor is usually connectedin a distribution system to provide reactive power compensationand, therefore, improves the quality of the electrical supply andenhances the efficient operation of the power system.

However, with its capacitive reactive power compensation,the contribution of a capacitor bank to current pulse is similarto that of a fault. When the voltage pulse is applied to a down-stream with a 2.5-Mvar shunt capacitor connected, the produced


Fig. 12. Effect of a capacitor on the current pulse.

Fig. 13. Harmonic resistance �� with a capacitor.

current pulse is shown in Fig. 12. As it can be seen, the currenthas a comparable magnitude as the fault current. It is thereforedifficult to distinguish a fault from a capacitor bank if only com-paring the currents waveforms in the time domain.

In the frequency domain, the capacitor almost has no contri-bution in the dc component (0 Hz) and its harmonic impedance

decreases as the frequency increases. After installing acapacitor bank in the system, the harmonic resistance ischanged

(13)

It is obvious that decreases rapidly with the in-crease of frequency. In contrast to this, the resistance in afaulted condition almost has no change in the low frequencies.When a capacitor is connected to the de-energized system, theharmonic resistance in a faulted condition and a normal condi-tion are compared in Fig. 13. It can be seen that with the increaseof frequency, the harmonic resistance decays rapidly when thereis a capacitor bank. However, if a fault exists, the change of har-monic resistance in low frequencies is very small. Thus, thisdifference provides a criterion for distinguishing a fault from acapacitor bank.

Furthermore, if a stalled motor and a capacitor bank exist inthe downstream, the harmonic impedance will not follow thepatterns discussed before since parallel resonance may occurwith the motor and the capacitor. For example, if the motorin Fig. 8 and the capacitor in Fig. 11 are both connected to

Fig. 14. Harmonic impedance when a 2.5 MVA capacitor and a 5000-hp motorare connected.

Fig. 15. Harmonic impedance when a 0.25 MVA capacitor and a 5000 hp motorare connected.

the de-energized system in parallel, the harmonic impedancewill become as shown in Fig. 14. Apparently, the parallel res-onance occurs at the frequency 180 Hz. The magnitude of theimpedance at resonance frequency is limited due to the exis-tence of the resistance. Generally, the resonance frequency de-pends on the system capacitance and reactance. If the capaci-tance is small, the resonance will occur at a higher frequency.Fig. 15 shows the simulation result when the 2.5 MVar capac-itor is replaced by a 0.25 MVar capacitor. Within the frequenciesbetween 0 360 Hz, the scenario of parallel resonance is notobserved. However, the difference between the faulted and theunfaulted cases is significant in Figs. 14 and 15. Thus, a sym-metrical fault can still be detected even though there is a parallelresonance introduced by a capacitor and a stalled motor.

Finally, with the aforementioned analysis for harmonicsimpedance characteristics under different situations, and com-bined with the asymmetrical fault detection method in [15], thefault detection procedure including the harmonic impedanceanalysis can be updated as follows.

1) Measure the currents and voltages of three phases after T1,T3, and T5 are fired simultaneously.

2) Are currents the same?


Fig. 16. Overall logic for symmetrical fault detection.

If No, turn to asymmetrical faults analysis (as in [15]).If Yes, calculate , , and by using theFourier transforms of the current and voltage with an FFTalgorithm.

i) If harmonic resonance is observed in , it in-dicates that a capacitor and a motor are connectedand the line is healthy.

ii) Otherwise, if has a large increase with theincrease of a frequency and is almost proportionalto the frequency, it indicates that a normal condi-tion or a stalled motor exists.

iii) Otherwise, if decays as frequency increases,a capacitor is connected without fault.

iv) If both and have no significant changeas frequency increases in the observed frequencies(0 360 Hz), it indicates that a symmetrical faultexists.

The overall logic for symmetrical fault detection based onharmonic impedance is summarized in Fig. 16.

III. LAB EXPERIMENT

A lab experiment based on a single-phase low-voltagesystem has been carried out to verify the proposed harmonicimpedance-based fault detection method. The laboratoryprototype consists of: 1) a thyristor-based signal gener-ator; 2) a NI-DAQ based data-acquisition system; and 3) alumped model-based equivalent circuit. Since the injectedcurrent is zero sequence in the proposed scheme, a single-phasesystem can effectively represent a balanced three-phase systemfor the research of symmetrical fault detection.

In the DAQ device, six channels are utilized—three of themare for voltage measurement and the other three are for currentmeasurement. The sampling rate in the voltages and currentsmeasurement is 1024 points every cycle, and a 1024-point FFTis performed for harmonic impedance analysis based on 60 Hz

Fig. 17. Diagram of the low-voltage lab test setup.

fundamental. The sampling rate is fast enough in this paper sincethe signal frequencies of interest are between 0 360 Hz. Insome cases, such as high-impedance fault detection, higher fre-quencies components are also considered as will be discussedlater.

Due to the limitations of lab equipment, the transmissionlines, transformers, and loads are replaced by equivalent R-Lmodels. The effects of an induction motor, which is connectedin parallel to the load, are also investigated. Moreover, to testthe performance of the proposed idea on the high-impedancefault detection, a tree branch and a box of dirt are used to simu-late high-impedance faults. The parameters of the componentsin this test are listed as follows, which is scaled down fromthe computer simulation model (with the same per-unit valuespreserved):

• power source: 120 V;• transformers: 0.03 p.u.,

0.76 mH;• signal generator: a thyristor; firing angle is adjustable from

170 to 150 ;• feeders: , 0.4 mH;• load: , 10 mH;• faults: resistance .The equivalent circuit of the lab test is shown in Fig. 17. The

fault resistance is adjustable. Three voltage probes and threecurrent probes measure the voltages and current at different lo-cations. The harmonic resistance and reactance arecalculated by the measured and .

Figs. 18 and 19 show the and in three differentconditions: 1) a bolted fault; 2) a fault with resistance ;and 3) no fault. It is seen that with a bolted fault is almostzero at all frequencies, which can be easily detected. On theother hand, increases slowly in both faulted situations butincreases fast in unfaulted situations, which is consistent withthe theoretical analysis.

To prove that the proposed idea has the ability of distin-guishing a fault from a stalled motor, a single-phase inductionmotor is connected to the test circuit and the parameters of themotor are listed in Table II. Since the induction motor is justlike a short circuit when it is stalled, it causes a high currentwhich is even larger than the fault current as shown in Fig. 20.To distinguish the stalled motor from a fault, in the twoconditions are illustrated in Fig. 21. It is apparent that thereactance of the downstream with a motor increases obviously


Fig. 18. Comparison of harmonic resistance ��.

Fig. 19. Comparison of harmonic reactance ��.

TABLE IIPARAMETERS OF THE INDUCTION MOTOR

Fig. 20. Effect of an induction motor on current waveforms.

in a normal condition, while this reactance with a fault is lessaffected by the increase of frequency.

In reality, a fault could occur on any ground condition, like atree branch, sand, mud, and dirt. The ground conditions affectthe characteristics of faults, and changes the fault resistance.Particularly, the high fault impedance is a challenge for faultdetection using the electrical signal. To investigate the perfor-mance of the proposed idea under a high impedance fault, two

Fig. 21. Harmonic reactance �� with a motor.

Fig. 22. High-impedance fault test with a tree branch.

Fig. 23. Current waveforms in a tree branch test.

experiments have been carried out. One is with a tree branch(Fig. 22). The tree branch is cut off from a live tree and its lengthis limited to 10 cm to lower the impedance. However, its resis-tance still reaches 16 k , even though it is wet. Fig. 23 showsthe currents obtained from the tree branch test. The resistanceof the branch is too high so that the fault current is almost zero.

Another high-impedance fault test is with a box of dirt(Fig. 24). The dirt comprises mud, little rocks, dead leaves,and water. The resistance is 5 k , which is lower than thetree branch but is still a high-impedance fault condition. Thefault current through a box of dirt is also very low as shown


Fig. 24. High-impedance fault test with a box of mud and dirt.

Fig. 25. Current waveforms in a mud and dirt test.

in Fig. 25. In this case, most of the injected current flowsthrough the connected loads rather than the box of dirt withhigh impedance.

The harmonic reactance in the high-impedance fault tests isshown in Fig. 26. Since there is no electrical response on the treebranch, the measured harmonic reactance in the faulted line andthe unfaulted line has almost no difference. The main reason forthe tree branch test not being effective is due to the low-voltagetest limitation. At higher voltage levels in a typical distribu-tion system, a stronger voltage pulse could cause actual faultarcs through a tree branch, which essentially reduces the faultimpedance and, therefore, helps the high-impedance fault de-tection.

To the contrary, the mud and dirt measurements had betterresults despite the fault current’s low magnitude. The harmonicreactance of the faulted line follows a flatter trend than theunfaulted line within a range of frequencies, such as between480 840 Hz. The distinction would likely improve in anactual situation, considering that the dirt had a much higherresistance than the rest of the scaled down circuit. Comparedto the tree branch test, we can see that the harmonic impedancebecomes more effective if there is current flowing through thefault. Once again, the situation can be expected to improve ata higher voltage level due to the arcs produced by the voltagedetection signal.

Fig. 26. Harmonic reactance �� in the high-impedance fault tests.

IV. CONCLUSION

This paper focuses on the development of a symmetricalthree-phase fault detection technique in a de-energized system,where the existence of a stalled motor or shunt capacitorbank makes the fault detection even more challenging as theybehave like short circuits. Compared to the asymmetrical faultdetection, the aforementioned situations require a detectiontechnique other than simply comparing the three-phase cur-rents. Thus, a new detection method based on the harmonicimpedance characteristics under the downstream circuit isdeveloped. The proposed method can be effectively used forsymmetrical fault detection and for distinguishing a fault froma stalled motor or capacitor bank. Finally, the fault detectionprocedure, including symmetrical and asymmetrical faults andwith consideration of possible stalled motor or capacitor banksat downstream, is presented. The proposed method has beenverified in computer simulations and lab tests.

This paper is supplementary to a companion paper [15],which presents the basic principle of the proposed power-elec-tronics-based fault detection technique and discusses theprocedure of asymmetrical faults detection. Combining thefindings in both papers, all different types of faults in thede-energized system can be identified.

REFERENCES

[1] V. L. Buchholz, M. Nagpal, and J. B. Neilson, “High impedance faultdetection device tester,” IEEE Trans. Power Del., vol. 11, no. 1, pp.184–190, Jan. 1996.

[2] S. P. Ahn, C. H. Kim, R. K. Aggarwal, and A. T. Aggarwal, “An alter-native approach to adaptive single pole auto-reclosing in high voltagetransmission systems based on variable dead time control,” IEEE Trans.Power Del., vol. 16, no. 4, pp. 676–686, Oct. 2001.

[3] M. M. Eissa and O. P. Malik, “A novel approach for auto-reclosingEHV/UHV transmission lines,” IEEE Trans. Power Del., vol. 15, no.3, pp. 908–912, Jul. 2000.

[4] C. G. Wester, “High impedance fault detection on distribution systems,”in Proc. 42nd Rural Elect. Power Conf., St. Louis, MO, 1998, pp. C51–5.

[5] IEEE Guide for Automatic Reclosing of Line Circuit Breakers for ACDistribution and Transmission Lines, IEEE Std. C37.104-2002, Apr.2003.


[6] G. D. Rockefeller, C. L. Rockefeller, J. L. Linders, K. L. Hicks, and D.T. Rizy, “Adaptive transmission relaying concepts for improved per-formance,” IEEE Trans. Power Del., vol. 3, no. 4, pp. 1446–1458, Oct.1988.

[7] M. M. Eissa and O. P. Malik, “A new digital directional transversedifferential current protection technique,” IEEE Trans. Power Del., vol.11, no. 3, pp. 1285–1291, Jul. 1996.

[8] J. F. Witte, S. R. Mendis, M. T. Bishop, and J. A. Kischefsky,“Computer-aided recloser applications for distribution systems,” IEEEComput. Appl. Power, vol. 5, no. 3, pp. 27–32, Jul. 1992.

[9] A. T. Johns, R. K. Aggarwal, and Y. H. Song, “Improved techniquesfor modeling fault arcs on faulted EHV transmission systems,” in Proc.Inst. Elect. Eng., Gen., Transm. Distrib., 1994, pp. 148–154.

[10] A. T. Trihus, “Cable tester,” U.S. Patent 4 254 374, Mar. 3, 1981.[11] D. A. Rhein and L. R. Beard, “Fault Detection System Including a Ca-

pacitor for Generating a Pulse and a Processor for Determine Admit-tance Versus Frequency of a Reflected Pulse,” U.S. Patent 5 650 728,Jul. 22, 1997.

[12] D. D. Wilson and Hedman, “Fault Isolator for Electrical Utility Distri-bution Systems,” U.S. Patent 4 370 609, Jan. 25, 1983.

[13] R. Maier and W. Roethlingshoefer, “Method and Arrangement for De-tecting Short-Circuit in Circuit Branches of Electrical Power SystemNetworks,” U.S. Patent 5 345 180, Sep. 6, 1994.

[14] S&C, “S&C IntelliRupter PulseCloser: Outdoor distribution 15.5 kVand 27 kV,” S&C Descriptive Bull. 766-30, Mar. 22, 2010.

[15] X. Long, W. Xu, and Y. Li, “A power electronics based fault detectiontechnique in a de-energized distribution system for safe recloser oper-ation,” IEEE Trans. Power Del., submitted for publication.

[16] W. Wang, E. E. Nino, and W. Xu, “Harmonic impedance measurementusing a thyristor-controlled short-circuit,” Inst. Eng. Technol.. Gen.,Transm. Distrib., vol. 1, no. 5, pp. 707–713, Sep. 2007.

[17] J. C. Gomez and M. M. Morcos, “A simple methodology for estimatingthe effect of voltage sags produced by induction motor starting cycleson sensitive equipment,” in Proc. 36th Ind. Appl. Soc. Annu. Meeting,Chicago, IL, Oct. 2001, pp. 1196–1199.

Xun Long (S’08) received the B.E. and M.Sc. degrees in electrical engineeringfrom Tsinghua University, Beijing, China, in 2004 and 2007, respectively, andis currently pursuing the Ph.D. degree in electrical and computer engineering atthe University of Alberta, Edmonton, AB, Canada.

His main research interests include power-line signaling, distributed genera-tion, and fault detection.

Yun Wei Li (S’04–M’05) received the B.Sc. degree in engineering degree fromTianjin University, Tianjin, China, in 2002, and the Ph.D. degree from NanyangTechnological University, Singapore, in 2006.

In 2005, he was a Visiting Scholar with the Institute of Energy Technology,Aalborg University, Denmark. From 2006 to 2007, he was a Postdoctoral Re-search Fellow in the Department of Electrical and Computer Engineering, Ry-erson University, Toronto, ON, Canada. After working with Rockwell Automa-tion Canada in 2007, he joined the Department of Electrical and Computer En-gineering, University of Alberta, Edmonton, AB, Canada, as an Assistant Pro-fessor. His research interests include distributed generation, microgrid, powerconverters, and electric motor drives.

Wilsun Xu (F’05) received the Ph.D. degree from the University of British Co-lumbia, Vancouver, BC, Canada, in 1989.

From 1989 to 1996, he was an Electrical Engineer with BC Hydro,Vancouver,and Surrey, BC, respectively. Currently, he is with the Department of Electricaland Computer Engineering, University of Alberta, where he has been since1996. His research interests are power quality and distributed generation.

Chris Lerohl (S’08) received the B.Sc. degree in electrical engineering from theUniversity of Alberta, Edmonton, AB, Canada, in 2009, where he is currentlypursuing the M.Sc. degree in power systems.

His main research interests include transmission-line signaling, distributedgeneration, and power system harmonics.

1902 ieee transactions on power delivery, vol. 26, no. 3,...

Documents