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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 26, NO. 1, JANUARY 2011 79

Controlled Closing of PT Delta Windingfor Identifying Faulted Lines

Ke Zhu, Peng Zhang, Wencong Wang, Member, IEEE, and Wilsun Xu, Fellow, IEEE

Abstract—It is very difficult to identify the line experiencing asingle-phase to ground fault in ungrounded and resonant groundedsystems. This paper presents a scheme for faulted line identifica-tion based on the concept of converting the ungrounded systeminto a grounded system in a controlled manner. This conversion orcontrolled grounding is done through the delta-winding of the po-tential transformers commonly available in substations. The delta-winding is inserted with a pair of SCRs and the controlled conduc-tion of the SCRs results in a temporarily closed delta and thus cre-ating a temporarily grounded system. This scheme is very easy toimplement and does not involve high voltage components. Resultsof theoretical analysis, computer simulation and lab experimentshave confirmed the effectiveness of the proposed method.

Index Terms—Faulted line identification, non-effectivelygrounded systems, ungrounded systems.

I. INTRODUCTION

U NGROUNDED AND resonant grounded neutrals arecommonly used in the power distribution systems of some

European and Asian countries and in several types of industrialfacilities in North America. When a single-phase-to-groundfault occurs, these configurations allow the distribution systemto continue to operate and significantly improve the servicereliability [1]–[3]. However, the faulted line must be identifiedand cleared within a required time frame (typically 30 min to 2h. Identifying the faulted line from a number of lines connectedto the same distribution bus is a significant challenge becausethe grounding condition only yields very small ground faultcurrents.

The aforementioned challenge has resulted in a great deal ofresearch work since the 1980s. Two types of methods have beendeveloped. The first type identifies the faulted line according tothe characteristics of the fault currents [4], [5]. These methodshave inherent limitations since the weak fault currents in un-grounded or resonant grounded systems cannot support accu-rate detections under a number of conditions. The second type

Manuscript received March 30, 2010; revised June 09, 2010; accepted July15, 2010. Date of publication September 13, 2010; date of current version De-cember 27, 2010. This work was supported by a grant from the Ph.D. Foundationof Shandong Province, China. (No. 2008BS01025). Paper no. TPWRD-00233-2010.

K. Zhu and W. Xu are with the School of Electrical Engineering, ShandongUniversity, Jinan 250061, China (e-mail: [email protected]; [email protected]).

P. Zhang is with the Hong Kong Polytechnic University, Hong Kong, China(e-mail: [email protected]).

W. Wang is with the University of Alberta, Edmonton, AB T6G 2V4, Canada(e-mail: [email protected]).

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

Digital Object Identifier 10.1109/TPWRD.2010.2064340

of methods actively injects specialized current signals into thesystem and identifies the faulted line according to the flow pat-tern of the signals [6]–[9]. However, the detection of the sig-nals can be difficult, especially when the fault resistance is highor the current waveforms are heavily polluted. Although manymethods have been proposed, there is still a need for a more re-liable detection scheme, especially in some highly polluted sys-tems such as coal mines and oil fields.

In response to the challenges, a faulted line identificationscheme using controlled grounding has been proposed in [10].The scheme converts an ungrounded system into a groundedsystem through an electronically-controlled grounding of thesubstation transformer neutral. The result is a controllableground fault current that is large enough for identifying thefaulted line and yet small enough not to cause system problems.Although the scheme can identify the faulted line reliably evenin some highly polluted systems, it is expensive to implementdue to the need to access to the transformer, a high voltageapparatus in the substation. Furthermore, the transformer’smagnetizing branch makes the system into a grounded system,which is not acceptabe for many facilities. To overcome thisproblem, this paper proposes to use the delta winding of thepotential transformers (PTs) commonly available in substa-tions to establish a controlled grounding condition. In theproposed scheme, a thyristor is inserted into the secondary(delta) winding of the PT which has a grounded primary perindustry standard. When the thyristor conducts, meaning thedelta is closed, the PT’s primary side will conduct a large con-trollable ground fault current. This pulse current is then used todetect the faulted line. This improved scheme is much easierto implement and costs significantly less. Theoretical analysis,simulations and experiments have verified the effectiveness ofthe proposed method.

This paper is organized as follows. Section II introduces theproposed scheme; Section III investigates the features of thetransient current signals flowing through the faulted line and theunfaulted line; Section IV proposes a criterion for identifyingthe faulted line and tests it under various conditions; Section Vanalyzes the influence of PT on the transient signal strength;Section VI shows laboratory test results of the scheme.

II. PROPOSED SCHEME

The problem of faulted line identification can be stated asfollows (see Fig. 1). An ungrounded substation provides powerto various loads through multiple three-phase distribution lines.When one of the lines experiences a ground fault, the systemcan still operate since the fault current is almost zero due to theungrounded arrangement of the system. However, there is a need

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80 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 26, NO. 1, JANUARY 2011

Fig. 1. Problem of faulted line detection.

to identify the faulted line as well as the fault location within aspecified time window due to safety concerns. Since the faultcurrent is very small, it becomes very difficult to find the lineexperiencing the ground fault among the multiple lines servedby the substation.

The cause of the small fault current is that the system is noteffectively grounded. If we temporarily convert such a systeminto a grounded system in a controlled manner, a large transientfault current will appear during the grounding period. This tran-sient current will flow through the faulted line and can be usedfor identifying that line. By controlling the period of grounding,we can create a ground fault current that is large enough to bedetected yet small enough not to cause disturbances to the loads.This idea is called controlled grounding.

We propose to use the substation PT as a platform to im-plement the controlled grounding. This scheme is illustrated inFig. 2. The standard PT has a grounded primary and a (open)delta secondary. The idea is to insert a controllable short-circuitcreator (CSCC) to the delta winding and to use it to close thedelta loop. When a ground fault occurs in the system, a voltagebuilds up between the system neutral and the ground, and alsothe terminals of the PT’s open delta. If the CSCC is used to closethe delta loop, the loop will generate a current during the con-duction period of CSCC. This is equivalent to creating a shortcircuit between the PT primary side neutral and the ground. Atransient fault current pulse will flow though the faulted line tothe ground. The signal detectors installed at the sending endof each line extract the transient fault current pulse from thezero-sequence current transformer (CT) outputs and identifywhich line is experiencing ground fault. The CSCC can be con-structed using several power electronic switching devices. Thesimplest of them is the thyristor. It can be seen that the proposedPT scheme offers a number of advantages in comparison withthe scheme of [10].

A. Controllable Short Circuit Creator

The structure of the thyristor-based controllable short-circuitcreator is shown in Fig. 3(a). The thyristor is fired ahead of thezero-crossing point of its terminal voltage falling edge, creatinga temporary short circuit at the PT delta coil. As shown in Fig.3(b), the system voltage waveform is distorted and a transient

Fig. 2. Illustration for the proposed scheme.

Fig. 3. Controllable short-circuit creator and the system responses duringthyristor conduction.

fault current flows through the faulted line, which can be usedfor faulted line identification.

The thyristor is fired in special ways in order to generate tran-sient current signals with distinct features to facilitate the de-tection. Firstly, by reducing the thyristor trigger angle , wecan increase the strength of the transient current signals untilthe faulted line can be identified. In this way, the controllableshort-circuit creator generates strong enough signals for identi-fication even when the fault resistance is relatively high. Second,the thyristor is not fired in every cycle, so that it can conductevery 2n fundamental cycles. As will be shownnext, this feature will make the proposed scheme much lesssensitive to harmonic currents in the distribution lines. Third,if two thyristors are connected in anti-parallel and are fired atthe voltage rising and falling edge, respectively, transient cur-rent pulses can be generated with two different polarities. Bycombining various frequency and polarity settings, a series oftransient pulses with distinct features can be created. This pulseseries can resist random noises and be easily detected.

B. Transient Current Detector

The transient current detector acquires the information of cur-rents flowing through each line according to the informationprovided by the controllable short-circuit creator, then extracts

ZHU et al.: CONTROLLED CLOSING OF PT DELTA WINDING FOR IDENTIFYING FAULTED LINES 81

Fig. 4. Subtraction method for extracting transient current signals.

the transient current signals, and finally identifies the faultedline.

An important feature of the proposed scheme is that the tran-sient current signal is extracted through subtraction of subse-quent cycles of the carrier waveform. As discussed earlier, thethyristor is not fired intentionally at every cycle. Assume thatit is fired every 4 cycles as shown in Fig. 4, the transient cur-rent signals can be obtained by subtracting the second two cy-cles containing no signal from the first two cycles containing asignal. This subtraction method is a powerful nonlinear filter inessence. It can greatly eliminate the background distortions con-tained in the current waveforms and make the proposed schemeimmune to periodic disturbances such as harmonics. As a result,the propose scheme is effective in highly polluted systems.

III. FEATURES OF THE TRANSIENT CURRENT SIGNALS

A. Theoretical Analysis of the Transient Current Pulse

Consider the system in Fig. 2. According to the superpositionprinciple, the thyristor firing process is equivalent to the injec-tion of a reverse voltage source at the position of the thyristor.This voltage source is applied to the three delta-connected coilsat the PT second side, and is induced to the grounded Y con-nected PT primary side. Fig. 5(a) shows the unbalanced three-phase equivalent circuit seen from the PT primary side. As-suming all the distribution lines have the same length. Fig. 5(b)shows the simplified sequence-circuit of Fig. 5(a), whereis the steady-state zero-sequence voltage caused by the single-phase-to-ground fault; and are, respectively, the leakage

Fig. 5. Analysis circuit for created transient current signals.

resistance and leakage inductance between the first winding andthe second delta winding of the distribution bus PT; is thesingle-phase zero-sequence capacitance of each line; is thefault resistance; is the number of distribution lines; is thetransient current pulse flowing through is the transientcurrent pulse flowing though is the total transient currentpulse flowing through the neutral of the PT high voltage side.All these quantities are assuming their values at the high voltageside of the PT.

Assuming the thyristor is fired at the instant with atrigger angle of (i.e., ), where

is the peak value of , and is the angular speed of . Theequation of the transient current pulses during thyristor conduc-tion is derived according to Fig. 5(b) as follows:

The triples of the zero-sequence transient currents flowingthrough the faulted line and an unfaulted line (denoted as and

, respectively) are used to identify the faulted line, and

(2)

The total current flowing through the neutral of the PT highvoltage side is

(3)

As the value of varies, the transient process caused bythyristor firing can be either over-damped or under-damped.Equation (1), shown at the bottom of the page, is presented ina way to facilitate the analysis of and when the transientis under-damped (i.e., oscillatory). According to (1)–(3), when

(1)


the transient process is under-damped, and both con-tain fundamental components of -frequency, as well as oscil-latory and damped components of -frequency. In typical cases

; therefore, the fundamental component containedin is much larger than that contained in .

Analysis has also been done for resonant grounded systemsand the equations of and during thyristor conduction havebeen derived. However, since these equations are relatively com-plicated, and and last much larger than the thyristor con-duction in resonant grounded systems, the features of transientcurrents in resonant grounded systems are analyzed in the nextsection through simulations.

B. Computer Simulations

The power system simulation block of the Matlab/Simulinksoftware is used to verify the proposed faulted line identificationscheme. The following system parameters are used:

Distribution system: 10 kV, 50 Hz, ungrounded, or reso-nant grounded through an arc suppression coil of 4.5 H;

Distribution lines: totally 10 lines, each of 20km, and /km, mH/km,

F/km, /km,mH/km, F/km;

Load: each distribution line has a three-phase load of 1MW with power factor of 0.8, ungrounded Y connected.Each phase of the load is composed of a 64 resistance inseries with a 0.15 H inductance.

Distribution bus PT: the real parameters of JDZX11-10BG type PT is adopted for simulation. The primaryvoltage is 10 kV, the secondary voltage is 100 V. Theleakage impedance between first and second side deltacoil is (the value is referred to the highvoltage side).Single-phase-to-ground fault: occurs at the phase A of the

end of one line; the fault resistance is adjustable.Fig. 6 shows the transient current waveforms of the un-

grounded system with and which areobtained through both simulations and deduction. The cor-responding oscillation frequency . The theoretical

and results using (1)–(3) were found to agree withthe simulation results very well during thyristor conduction,and the theoretical is plotted in Fig. 6(a) for comparison.Apparent differences existed between the waveforms ofand . Fig. 6(b) verifies the analysis using (1)–(3) in III.Athat and both contain fundamental components of , aswell as an oscillatory and damped component of 0.5 . Thefundamental and oscillatory component contained in is muchlarger, respectively, than that contained in . Fig. 6(c) showsthe faulted phase A to neutral voltage at the load terminal andthe voltage transient during thyristor conduction. As can beseen, the peak voltage transient caused by thyristor conductionis about 0.1% of the peak load voltage and therefore has anegligible impact to the load.

An important feature of the proposed scheme is that themagnitude of the transient current pulses can be adjusted bychanging the thyristor trigger angle , so that enough signalstrength is available for identifying the faulted line as the faultresistance varies. Fig. 7 presents the waveforms of and

Fig. 6. Transient responses of the ungrounded test system with � �

�� .

Fig. 7. Responses of the ungrounded system with � or � varies. (a) � �

�� varies. (b) � � �� varies.

in the ungrounded system under various trigger angle andfault resistance values according to simulations. It is foundthat:

1) as the thyristor trigger angle decreases, the thyristor con-duction time increases; the magnitude of the positive pulsesof increases, while the magnitudes of remains at arelatively low level;

2) as the fault resistance increases, the magnitude ofdecreases due to the reduction in the coefficient of

; although the magnitude of varies, it is still ina low level.


Fig. 8. Transient current pulses of a resonant grounded system with � � ��

and � vary.

According to simulations in the resonant grounded system,the variation tendencies of and with respect to andare similar to those in the ungrounded system. However, dueto the current-sustaining effect of the arc-suppression coil, the

and pulses last for a long time after the thyristor ex-tinction. Fig. 8 shows the waveforms of and for theresonant grounded system when and the fault resis-tance varies. In this figure, since has little impact onthe zero-sequence voltage caused by the fault, and it is muchsmaller than the leakage impedance of the distribution bus PT,the variation of does not affect the thyristor conduction timetoo much. However, when the is relative higher, for example

, due to the influence of the arc-suppressioncoil, the and can last about 2 fundamental cycles afterthe thyristor extinction. Therefore, in order to accurately extractthe transient current signals using the subtraction method, thethyristor should be fired at an interval of more than 4 funda-mental cycles.

IV. DETECTION CRITERION FOR THE FAULTED LINE

In this section, further analysis is carried out for the andsignals to search for a criterion to identify the faulted line in

both ungrounded and resonant grounded systems.

A. Construction of the Detection Criterion

The spectra of the transient current pulses in Figs. 7(a) and 8are calculated using FFT with the window length of one funda-mental cycle. The results are shown in Fig. 9(a) and (b), respec-tively. It is observed that:

1) for the ungrounded system, the energy of signal concen-trates in the dc and low-frequency components; the energyof is much lower than that of , and concentrates inthe low-frequency components.

2) for the resonant grounded system, the energy of con-centrates in the low-frequency components; the energy of

is much lower than that of , and concentrates in thelow-frequency components.

Fig. 9. Spectra of the transient current pulses. (a) The neutrally ungroundedtest system � � �� varies. (b) The resonant grounded test system � �

�� varies.

The aforementioned results can be explained as follows. Forthe ungrounded system, since the zero-sequence capacitoris a high-pass filter, the dc and most of the low-frequency com-ponents flow through the fault resistance instead of through

. So the dc and low-frequency components can be used todistinguish and in the ungrounded system.

For the resonant grounded system, since the arc-suppressioncoil is a low-pass filter, the dc component contained in thethyristor current flows through the arc-suppression coil.However, as long as , more low-frequency com-ponents will flow through than that through . Therefore,these low-frequency components can be used to distinguishand in a resonant ground system.

Based on the aforementioned results, the following criterionis constructed to distinguish and in ungrounded and res-onant grounded systems

(4)

where are, respectively, the dc, 1st, and 2nd harmoniccontained in the transient current pulse flowing through eachdistribution line. The faulted line will be identified as the onewith the largest .

B. Factors Influencing

According to ((1)–(4)), the thyristor trigger angle , the faultresistance , and the number of distribution lines have impactson .


Fig. 10. Influence of � on � .

Fig. 11. Influence of � on � � � � �� .

Fig. 10 presents the variation tendency of with re-spect to the trigger angle when is equal to 250 , 500 ,and 2000 , respectively. According to this figure, theof the faulted line increases as reduces, while theof an unfaulted line remains very low and close to zero. Sincethe neutral voltage in the resonant grounded system is hardly af-fected by the fault resistance , the faulted line of theresonant grounded system is larger than that of the ungroundedsystem when is high.

Fig. 11 demonstrates the impact of the fault resistance onwhen . As increases, the difference be-

tween the faulted line and unfaulted line diminishes.When , the fault line is about 2.7 timesof the unfaulted line in the resonant grounded system,while the corresponding zero-sequence voltage is only about25% of normal phase voltage value. Therefore, the differencebetween and based on the is obvious even whenthe fault resistance is very high.

Fig. 12 shows how varies with respect to the numberof distribution lines when , and and 90 ,respectively. The arc suppression coil inductance reduces ac-cordingly as the line number increases. As shown this figure,for the ungrounded system, the neutral voltage and the terminalvoltage of in Fig. 5(b) reduce as the line number increases,which makes the faulted line decrease. For the reso-nant grounded system, an increase in line number has little im-pact on the neutral voltage; however, it causes reduction in the

terminal voltage and, therefore, slowly reduces the faultedline . For both the ungrounded and resonant groundedsystem, the unfaulted line remains in a very low level,

Fig. 12. Influence of line number on � when � � �� .

and slightly reduces as the line number increases. To conclude,the variation in distribution line number has little impact onthe difference between the faulted line and the unfaulted line

.

V. INFLUENCE OF PT ON TRANSIENT SIGNAL STRENGTH

Although the strength of the transient current pulse can becontrolled through the thyristor trigger angle, it needs to injectthis current into the system through the special transformer PT.so the current limiting influence of PT must be considered.

On one hand, the PT leakage impedance in the Fig. 5(b)is high due to its high ratio, which may lead to the transientcurrent pulses too small to be detected. To solve the problem,an extra voltage source can be inserted into the PT secondarydelta winding if necessary to support a transient current signalstrong enough to be reliably extracted from the zero-sequenceCT outputs. The extra voltage source can only increase thesignal strength and has no effect on the difference of andbased on the .

On the other hand, the constraint of PT small capacity onthe transient current signals’ strength must also be considered.However, since the proposed scheme injects momentary tran-sient current signals to the system, the current limiting influenceof PT small capacity is not obvious. Moreover, the limitation oncurrent signal strength can be released further by using lowerthyristor firing frequency, so that strong enough current signalscan be injected for identification.

For the power distribution systems in China, the resonant sys-tems are recommended to reduce the fault current magnitude ifthe rms of single-phase to ground fault currents exceeds 10 A.According to this information, 4% of this fault current, namely,about 560 mA in magnitude, is assumed as the signal strengthlower limit, which ensures the signal to be extracted from back-ground. In addition, for the type of PT which is used in the simu-lation, the largest rms of current injected into the delta coil in thePT secondary side is 9 A, which is calculated through its sec-ondary delta coil thermal limiting output. Fig. 13 presents thesimulation curve of relationship between the relative magni-tude, namely, the ratio of magnitude and A, and rms ofPT delta coil current. The thyristor trigger angle varies from 0to 180 at 20 intervals. The thyristor is fired at 25 fundamentalcycles in order to weaken the limit of the PT small capacity onthe rms of delta coil current. The relative magnitude higherthan 4% and the RMS of PT delta coil current smaller than 9


Fig. 13. Analysis of the proposed scheme operable region influenced by PT.

Fig. 14. Ungrounded laboratory test system.

A represents the operable region. From the figure, we can seethat the proposed scheme still has about 40 valid work rangeeven for the ungrounded systems. A curve of

for the ungrounded systems after inserting a 100V RMS extra voltage source in the PT delta coil and with thefiring period of 50 fundamental cycles is drawn also. By com-paring the two curves of for the ungrounded sys-tems we can see, inserting extra voltage source in the PT deltacoil and extending thyristor firing period can extend the oper-able region effectively when the fault resistance is very high.

VI. LABORATORY TESTS RESULTS

The proposed scheme has been verified through laboratorytests. The test system was established by scaling down thevoltage of a 10 kV typical distribution system to 220 V andmaintaining the impedance values. Limited by the lab condi-tions, the system only contained two identical distribution lines,each modeled with a equivalent circuit. A three-phasetransformer was constructed with three single-phase 200 VA,243/57.8 V transformer, and was connected to the distributionbus. The controllable short-circuit creator in series with acurrent-limiting impedance was connected to the open loop ofdelta connection. The ungrounded test system is illustrated inFig. 14, with the circuit parameters listed in Table I.

Fig. 15 presents the transient current pulses obtained in thelaboratory tests. The current values have been amplified by aratio of 10000/220. The difference in pulse magnitude betweenthe Figs. 15 and 7(a) is caused by the current-limiting impedance

TABLE IPARAMETERS OF THE LABORATORY TEST SYSTEM

Fig. 15. Transient current pulses obtained in laboratory tests. (a)� � ��.(b) � � �� .

and leakage impedance of single-phase transformer in lab test,which are smaller than the PT leakage impedance. This figureclearly shows the variation tendencies of the transient currentpulses with respect to and , which coincide with the abovecomputer simulation results.

Fig. 16 shows the variation of with respect to andfault resistance according to the test results. The variationtendencies agree with the simulation results in Section IV-Balso.

VII. CONCLUSION

This paper has proposed an effective and low cost method forfaulted line identification in ungrounded and resonant groundeddistribution systems. A thyristor-based device is inserted into


Fig. 16. Variations of � in the laboratory tests. (a) � � �� . (b)� � �� .

the secondary delta loop of substation PT and is fired to closethe delta loop when a ground fault occurs in the system, whichis equivalent to creating a short circuit between the PT primaryside neutral and the ground and will create transient currentpulses flowing though the faulted line. The detection of the pulsecurrent helps to identify the faulted line.

The impact of the PT delta loop short circuit to the powerquality is negligible due to the high PT leakage impedance. Acriterion was developed for identifying the faulted line basedon the spectra of the transient current pulses. The influences oftrigger angle, fault resistance, number of feeders, and the PTon the criterion are analyzed. Theoretical analysis, simulations,and experiments have verified the effectiveness of the proposedmethod. The proposed scheme is very easy to implement andthere is no need to access high voltage equipment. It can be apromising solution to the problem of faulted-line identificationin non-effectively grounded distribution systems.

REFERENCES

[1] D. H. Lubich, “High resistance grounding and fault finding on threephase three wire (Dalta) power systems,” in Proc. IEEE Annual Tech.Conf. Textile, Fiber, and Film Industry, May 1997, pp. 10–15.

[2] J. P. Nelson, “High-resistance grounding of low-voltage systems: Astandard for the petroleum and chemical industry,” IEEE Trans. Ind.Appl., vol. 35, no. 4, pp. 941–948, Jul./Aug. 1999.

[3] T. Baldwin, F. Renovich, L. F. Saunders, and D. Lubkeman, “Faultlocating in ungrounded and high-resistance grounded systems,” IEEETrans. Ind. Appl., vol. 37, no. 4, pp. 1152–1159, Jul./Aug. 2001.

[4] T. Baldwin, F. Renovich, and L. F. Saunders, “Directional ground-fault indicator for high-resistance grounded systems,” IEEE Trans. Ind.Appl., vol. 39, no. 2, pp. 325–332, Mar./Apr. 2003.

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[6] J. C. Das and R. H. Osman, “Grounding of AC and DC low-voltageand medium voltage drive systems,” IEEE Trans. Ind. Appl., vol. 34,no. 1, pp. 205–216, Jan./Feb. 1998.

[7] Z. Sang, H. Zhang, and Z. Pan, “Protection for single pahse to earthfault line selection for ungrounded power system by injecting signal,”Autom. Elect. Power Syst., vol. 20, no. 2, pp. 11–12, 1996.

[8] Y. Liu, J. Gong, and G. Wei, “Analysis and improvement of the S in-jection fault feeder detection method,” J. Shandong Univ. (Eng. Sci.),2007, 4.

[9] X. Zeng, X. Yin, Y. Yu, and D. Chen, “New methods for control andprotection relay in a compensated medium voltage distribution networkbased on injecting various frequency current,” in Proc. CSEE, 2000, 01.

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Ke Zhu received the Ph.D. from Shandong University, China, in 2007.He has been with the faculty at the School of Electrical Engineering, Shan-

dong University, Jinan, China, since 2007. His research interests are power sys-tems and fault detection.

Peng Zhang received the B.Sc. and M.Sc. degrees in electrical engineering fromShandong University, China, in 2004 and 2007, respectively, and is currentlypursuing the Ph.D. degree at the Hong Kong Polytechnic University.

His main research includes power systems and fault detection.

Wencong Wang (M’09) received the B.Sc. and M.Sc. degrees from TsignghuaUniversity, Beijing, China, in 1999 and 2003, respectively, and the Ph.D. degreefrom the University of Alberta, Edmonton, AB,. Canada, in 2009.

Currently, she ix with BC Hydro., Vancouver, BC, Canada. Her main researchinterests are distributed generation and ground fault detection.

Wilsun Xu (M’90–SM’95–F’05) received the Ph.D. degree from the Universityof British Columbia, Vancouver, BC, Canada, in 1989.

From 1989 to 1996, he was an Electrical Engineer with BC Hydro, where hewas responsible for power quality and voltage stability projects. Currently, he isan Adjunct Professor at Shandong University, Shandong, China, and a Professorat the University of Alberta, Edmonton, AB, Canada. His main research interestsare power quality, voltage stability, and distributed generation.

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