Electrical Power and Energy Systems 52 (2013) 81–86

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Electrical Power and Energy Systems

journal homepage: www.elsevier .com/locate / i jepes

Equal transfer processes-based distance protection of EHVtransmission lines

0142-0615/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.ijepes.2013.03.028

⇑ Corresponding author. Tel./fax: +86 2787540945.E-mail address: swenmh@mail.hust.edu.cn (M. Wen).

Minghao Wen ⇑, Deshu Chen, Xianggen YinState Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Hubei, China

a r t i c l e i n f o

Article history:Received 4 July 2011Received in revised form 6 February 2013Accepted 28 March 2013Available online 23 April 2013

Keywords:Coupling capacitor voltage transformerDistance relayEqual transfer processVirtual digital transfer

a b s t r a c t

The overreach of the distance protection caused by CCVT is still a serious problem for high-speed line pro-tections. Based on the theory of Equal Transfer Process of Transmission Lines (ETPTLs), a new high-speeddistance relay scheme is proposed in order to overcome above problem. The solution is to make thethree-phase voltages and currents at the relay location and the voltage at the fault point have the sametransfer links by virtue of a new design. Three major steps of the new method are demonstrated: re-structuring of the voltage at the fault point, the virtual digital transfer method and solving the R–L dif-ferential equation. A variety of ATP simulation tests show that the new method effectively reduces thetransient error caused by CCVT and improves the operating speed by a series of technical countermea-sures including three major steps, iterative calculations of the fault distance and an inverse time delaysetting criterion. The distance measuring error is within 5% at approximately 15 ms after fault occur-rence, which is superior to various adaptive protection algorithms based on CCVT transient error estima-tion or source impedance ratio (SIR).

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Distance protection is the foremost protection to protect thetransmission line without needing the channel [1–6]. However,the overreach of the distance protection caused by CCVT is still aserious problem for high-speed line protections. Presently, CCVTis extensively applied to the power systems of 330 kV, 500 kVand above in China. Under normal conditions, the primary powersystem operates at steady-state. In this case, the transferring accu-racy of CCVT is satisfactory. However, the system voltage dropssuddenly when a fault occurs on any part of the transmission net-work. The output of the CCVT cannot trace the input simulta-neously due to the very large capacitance and inductance of theCCVT, and the transient process may last for a long period of time.

The transient characteristics of CCVT distort the linear transferrelationship between the secondary voltage injected to the protec-tion device and the primary voltage of the line, which may lead tothe transient overreach of distance protections and endanger thesecurity and stability of power systems [7–11]. In China, thezone-I setting of the distance protection is set as 0.8 time of the fullline impedance. In order to avoid the transient overreach, the pro-tection reach only can be up to 24% of the total length of the line ifthe protection is required to operate within between 5 ms and

10 ms. 56% of the total length can be protected if the operatingtime is required to be between 10 ms and 20 ms. It has been dis-closed that the degree of transient overreach caused by CCVT isin relation to SIR [11].

At present, the usual approach preventing the protection fromthis type of overreach is to add additional time delay. However,in order to improve the operating speed and the reliability of dis-tance protections, many studies are conducted on CCVT simulationand how to improve the transient response characteristics of CCVT.Some methods are proposed, e.g., transient error est based method.Different time delay strategies are adopted according to the quan-tity of error. In this case, the operation speed is enhanced com-pared with the regular distance protection [12].

The measurement error can be estimated by means of the quan-tity of SIR. This error is small when SIR is relatively small. In thiscase, time delay to issue the trip signal can be reduced [13]. What’smore, the combination of various digital filter algorithms can beadopted to improve the accuracy of fault measurement by reducingthe impact of the transient component of CCVT [14]. These meth-ods, however, only partly improve the accuracy of fault measure-ment. Therefore, the effect of reducing the time delay ofprotection tripping is not satisfactory. The most ideal method isthe recurrence of the input voltage of CCVT.

However, it is very difficult to reconstruct the input signalaccording to the output signal of a complex circuit. In [15], a sim-plified model of CCVT and corresponding parameters are used to

82 M. Wen et al. / Electrical Power and Energy Systems 52 (2013) 81–86

correct the measuring error of the secondary voltage, which can re-duce the error to some extent. However, the transient measuringerror during the first cycle after fault inception is still quite big.

The voltage and current signals used by distance protection de-vice do not match the corresponding actual signals of protectedline due to the transfer of CCVT, which results in the transientoverreach of distance relays. In order to prevent the distance relayfrom transient overreach, it is necessary to guarantee that the volt-age difference between the relay location and the fault point withrespect to the current measured by the distance relay can complywith the real transmission line model of taking the distributionparameters into account.

It is pointed out by ETPTL[16,17] that the relationship betweenthe distributed voltage and the current of a transmission line doesnot change if they are transformed by the same linear circuit andstill comply with the distribution parameter model of the originaltransmission line. Generally, CCVT can be regarded as a lineartransfer circuit since the intermittent transformer of CCVT alwayswill not saturate. Therefore, for the purpose of allowing the voltagedifference between the relay location and the fault point with re-spect to the current measured by the distance relay to comply withthe distributed parameter model of the original transmission line,both the transfer links for the voltage and the current signals at therelay location, as well as that for the voltage at fault point shouldbe consistent.

To solve above problems, a fast distance protection scheme thatcan prevent from the transient overreach caused by CCVT is putforward. Three countermeasures are introduced. Firstly, the volt-age at the fault point is restructured. The pre-fault voltage at thefault point is regarded to be close to the bus voltage at the relaylocation, and the post-fault voltage at this point is regarded asthe voltage drop on a fault resistance. Secondly, a virtual digitaltransfer method is adopted, which can ensure that the current atthe relay location and the voltage at the fault point pass the virtualdigital transfer link whose transfer characteristic is the same asthat of the actual CCVT equipped at the relay point. Thirdly, theR–L differential equation algorithm can be used to solve the faultdistance by using the voltage at the relay position, which is trans-ferred by the real CCVT, together with the current through the re-lay point, which is transferred by the virtual CCVT, and the voltageat the fault point, which is transferred by the virtual CCVT.

Fig. 1. CCVT circuit: (a) actual circuit; (b) equivalent circuit.

2. A fast distance protection method

2.1. Restructuring of the voltage at the fault point

When the CCVT is not applied to a transmission line, the busvoltage measured by the conventional distance relay is actuallythe voltage difference between the relay location and the faultpoint in the case of bolted faults. It is because that the voltage atthe fault point is zero in this scenario. Therefore, this voltage andthe line current comply with the model of the protected line. Whenthe CCVT is used for a distance relay to measure the voltage,according to ETPTL, the relationship of the voltage difference be-tween the relay location and the fault point with respect to the cur-rent measured by the relay cannot comply with the distributedparameter model of the protected line unless the measured currentof the distance relay and the voltage at the fault point also pass theCCVT linear transfer circuits which are the same as that for the busvoltage measurement.

The voltage at the fault point can be regarded as zero when abolted fault takes place. However, this voltage does not suddenlydrop to zero at the moment of the fault inception if it passes theCCVT linear transfer circuit. Instead, a transient process should ex-ist and last for dozens of milliseconds. If this transient process is

neglected and the voltage at the fault point passing the CCVT linearcircuit transfer is simply regarded as zero, the transient overreachof the distance relay will possibly occur to a great extent. It is nec-essary to estimate the voltage at the fault point according to thethree-phase voltages and currents at the relay location that canbe measured by the distance relays.

The process of restructuring the voltage at the fault point can bedivided into two stages, namely, the pre-fault one and the post-fault one. In general, the pre-fault voltage at the fault point is asinusoidal steady-state signal. The compensated voltage at a cer-tain point of the protected line is used as the estimation of thisvoltage since the fault position is unpredictable.

Two scenarios should be taken into account during the stage ofpost-fault. Firstly, the voltage at the fault point can be regarded aszero in the case of bolted faults. Secondly, this voltage at the faultpoint can be regarded as the voltage drop on the fault resistance inthe case of the grounding fault via a fault resistance. The voltagedrop on the fault resistance can be expressed as the product ofthe current passing through the fault resistance multiplied by thefault resistance. According to the usual realization method of dis-tance protection, the current through the fault resistance in thecase of the grounding fault via a fault resistance is replaced withzero sequence current measured by the distance relay. The currentthrough the fault resistance in the case of a phase-to-phase faultvia fault resistance is replaced with the current of the faulty phase.In this case, the value of the fault resistance can be taken as a var-iable to solve. Therefore, the post-fault voltage at the fault pointcan be uniformly set as the voltage drop on the fault resistance,i.e., the product of the fault resistance and the current throughthe fault resistance. If the solution of this fault resistance is nearlyequal to zero, this fault should be a bolted fault.

2.2. Virtual digital CCVT transfer method

A virtual digital CCVT transfer method is adopted, which can en-sure that the currents at the relay point and the voltage at the faultpoint pass the virtual digital transfer link whose transfer character-istic is the same as that of the actual CCVT equipped at the relaypoint. So the problem about the difference between the transferfeature of the voltages at the relay point and that of the currentsdue to the transient characteristic of CCVT can be solved. The

M. Wen et al. / Electrical Power and Energy Systems 52 (2013) 81–86 83

virtual digital CCVT circuit is identical to the actual CCVT equiva-lent circuit as shown in Fig. 1b. The more detailed process of thevirtual transfer method can refer to literature [16].

2.3. Application of R–L differential equation algorithm

During the transient course due to fault occurrence, Sub-har-monics and decaying DC components contained in the currentsamplings have adverse impact on the performance of the phasorbased distance protection. The distributed capacitance of the lineis not taken into account for the R–L differential equation baseddistance relaying algorithm. Hence, its high-frequency characteris-tics are not satisfactory. The virtual transfer method is adopted inthe proposed distance protection algorithm. The voltage at the re-lay location is transformed by CCVT, meanwhile, both the currentthrough the relay location and the voltage at the fault point usedby the distance protection algorithm are also processed by the vir-tual digital transfer links having the same CCVT transfer character-istic. The capacitance and the inductance in CCVT circuit could leadto series resonance at the frequency close to the power frequency,which will restrain the high frequency components of input signalsto a great extent. In this case, the shortcomings of R–L differentialequation algorithm due to the impact of high frequency compo-nents can be overcome. Therefore, the application of R–L differen-tial equation algorithm is promising to achieve relatively goodprotection performance.

The implementation of R–L differential equation algorithm inthe new protection scheme is demonstrated by taking the single-phase-to-earth fault as an illustration. When a single phase toearth fault via the fault resistance Rf occurs at point F on the line,we have.

umðtÞ¼ uf ðtÞ

þ L1dðimðtÞ� im0ðtÞÞ

dtþR1ðimðtÞ� im0ðtÞÞ

�þL0

dim0ðtÞdt

þR0 � im0ðtÞ�� l

ð1Þ

where um(t) is the faulty phase voltage at the relay point; im(t) thefaulty phase current at the relay point; uf(t) the faulty phase voltageat the fault point F; im0(t) the zero sequence current at the relaypoint; L1 and R1 the positive sequence inductance and resistanceof the line per unit length; L0 and R0 the zero sequence inductanceand resistance of the line per unit length; l the distance from the re-lay point to the fault point F; Rf is the fault resistance.Here, uf(t) isthe function of Rf as described in Section 2.1. One-point differentialalgorithm is adopted to perform the differential calculation, as gi-ven by:

dðimðtÞ � im0ðtÞÞdt

� �t¼nDt

¼ ½imðnþ 1Þ � im0ðnþ 1Þ� � ½imðnÞ � im0ðnÞ�Dt

ð2Þ

where Dt is the sampling interval and n is the index of thesamplings.

If a series of samplings in a certain period are substituted into(1), a series of differential equations are available correspondingly.They can compose of a set of the equations. In this paper, the leastsquare algorithm is used to calculate the distance from the relaypoint to the fault point.

2.4. Iterative calculations of the fault distance

A data window with 5 ms window length starting from the mo-ment of fault inception is used to calculate the fault distance basedon the proposed method. The sampling rate is set as 4800 Hz in thecase of 50 Hz power frequency. A moving data window is used, thatis, the oldest one is moved out when a new sample enters this win-

dow and the algorithm is re-executed. The calculation procedure isdetailed as below.

Step 1: New samplings of three phase currents are obtained byprocessing three phase currents with virtual CCVT transferringlink.Step 2: Define t0 be the moment of fault occurrence, and tjs bethe current calculation moment, we have

tjs ¼ t0 þ 5 ms ð3Þ

t0 can be determined by the pick-up element, which is imple-mented with the over-current relay with respect to the superim-posed components of phase-phase current together with thezero-sequence over-current relay.

Step 3: Define the iteration value to calculate the fault distancebe D0 = 0.5 Dl, Dl is the length of the protected line.Step 4: Calculate the samplings of the voltage at the fault pointduring the period between t0 � T and tjs, where T is 100 ms.Step 5: Processing the samplings of the voltage at the fault pointduring the period between t0 � T and tjs by means of virtualCCVT transfer link to obtain the new samplings.Step 6: Substitute the three-phase voltage samplings, togetherwith the samplings of the new three-phase currents, and thevoltage at the fault point into R–L differential equation to calcu-late the fault distance D during this period of time.Step 7: Turn to step 8 if tjs – t0 < 50 ms, else turn to step 10.Step 8: Define

tjs ¼ tjs þ ð20=96Þms ð4Þ

Step 9: Let D0 = D and turn to step 4.Step 10: End.

In this way, we have every fault distance calculation result foreach sampling instance during the post-fault period of 50 ms timelength.

2.5. An inverse time delay setting criterion

The inverse time delay setting criterion can be used for the pro-posed new scheme, as described below:

For the small SIR system(SIR < 10), as long as the pick-up ele-ment operates, we set Zset = 0.5ZL in the case of tpost-fault = 8 ms,set Zset = 0.8ZL in the case of tpost-fault = 10 ms, and set Zset = 0.95ZL

in the case of tpost-fault = 15 ms. ZL is the impedance of the protectedline.

For the big SIR system(10 < SIR < 20), as long as the pick-up ele-ment operates, we set Zset = 0.5ZL in the case of tpost-fault = 12 ms,set Zset = 0.8ZL in the case of tpost-fault = 15 ms, and set Zset = 0.95ZL

in the case of tpost-fault = 25 ms.

3. Simulation analysis

A variety of simulation tests show that the new method effec-tively reduces the transient error caused by CCVT. The new methodis compared with several existing distance protection schemes tohighlight its advantages. The existing distance protections includethe conventional differential equation based distance relayingalgorithm, half-cycle Fourier Algorithm and full-cycle Fourier Algo-rithm [18–21]. The impedance measurement calculation methodsof various adaptive algorithms in [12,13] are also based on thesealgorithms.

The tests have been done based on Alternative Transients Pro-gram version of EMTP (ATP). The schematic diagram of the

Fig. 2. The schematic diagram of simulation system.

Table 1Parameter list of CCVT equivalent circuit.

Circuitparameter

Value Parameter ofdamper

Value Parameterof load

Value

L1 H 142.1274 Cf lF 0.015858 Rb k X 1352.0R1 k X 1.95055 Lf H 639.576 Lb H 3229.3Ce lF 0.078567 rf k X 6.0

Rf k X 131.8

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500 kV power system is shown in Fig. 2. Here u(t) and i(t) are volt-ages and currents sampled by the protection, and D is the linelength. The line parameters are D = 100 km, r = 0.027 X/km,x = 0.28 X/km, r0 = 0.195 X/km and x0 = 0.649 X/km. Data for net-work A are: RA = 0.42 X, LA = 0.106 H, RA0 = 0.188 X, and LA0 =0.036 H. Data for network B are: RB = 0.63 X, LB = 0.16 H,RB0 = 0.28 X, and LB0 = 0.054 H. The equivalent electromotive forcesof networks A and B are EA = 525 kV and EB = 500 kV respectively.The phase angle between them is 30�. The parameters of CCVTare shown in Table 1. The sampling rate is set as 4800 Hz in thecase of 50 Hz power frequency.

A data window with 5 ms window length starting from the mo-ment of fault inception is used to calculate the fault distance based

Fig. 3. Time–impedance curves when SIR = 6: (a) the curve of the new method, (b) thealgorithm, (d) the curve of the full-cycle Fourier algorithm.

on the proposed method (as described in Section 2.4). The time-impedance curve can be obtained. The horizontal axis in the figurerepresents the moment at which the data window end is. Here, thefault occurrence is taken as the initial moment. The longitudinalaxis stands for the measuring impedance. The measured imped-ance is expressed in per unit with respect to the actual line imped-ance between the fault point and the relay location.

Similarly, the time-impedance curves can be obtained for otherexisting distance protections. The least square method with a 5 msdata window is adopted to obtain the fault distance when execut-ing the differential equation based algorithm. For the half-cycleand full-cycle Fourier Algorithms, the phasors of three-phase volt-ages and currents at the relay location are calculated prior toobtaining the measuring impedance from the fault point to the re-lay location. For the convenience of comparison and analysis,4800 Hz sampling rate is adopted for all these four algorithms.

Fig. 3 shows the time-impedance curves in the case of SIR = 6,l = 20 km and RF = 0.1 X. The curve begins at 5 ms since the mini-mum data window of the new method is 5 ms. Similarly, the curveformed by the solving-differential-equation algorithm begins at5 ms. Besides, the curve formed by the half-cycle Fourier algorithmbegins from 10 ms, and the curve formed by the full-cycle Fourieralgorithm begins from 20 ms.

There are some fluctuations at the initial moment for these fourtime-impedance curves, and then the measuring impedances allgradually approach 1. Here two time indexes are used to analyzeand compare the four distance protection algorithms, namely, themoment t0.9–1.1 corresponding to the measuring impedance withthe convergence of 0.9–1.1, and t0.95–1.05 corresponding to the mea-suring impedance with the convergence of 0.95–1.05.

Here we have t0.9–1.1 = 14 ms and t0.95–1.01 = 15 ms for the newmethod. In comparison, we have t0.9–1.1 = 28 ms and t0.95–1.05 = 58ms for the solving-differential-equation algorithm, t0.9–1.1 = 31 msand t0.95–1.05 = 42 ms for the half-cycle Fourier Algorithm,t0.9–1.1 = 32 ms and t0.9–1.05 = 34 ms for the full-cycle Fourier Algo-rithm. If the setting impedance is 1, in accordance with the relay

curve of the differential equation algorithm, (c) the curve of the half-cycle Fourier

Table 2Some typical simulation results (ms).

l = 20 km SSIR = 6 l = 40 km SSIR = 3 l = 60 km SSIR = 2 l = 80 km SSIR = 1.5

SGF t0.9–1.1 9 8 8 8t0.95–1.05 14 9 8 13

PPF t0.9–1.1 13 12 12 6t0.95–1.05 14 13 13 13

TPF t0.9–1.1 14 14 13 8t0.95–1.05 16 16 15 12

M. Wen et al. / Electrical Power and Energy Systems 52 (2013) 81–86 85

protection test specification which allows 5% transient overreach,the relay based on the new method can operate at 15 ms. In con-trast, the other three distance protections operate with longer timedelay. Among which, the full-cycle Fourier Algorithm based meth-od, the fastest one of these three algorithms, needs 34 ms tooperate.

Actually, for various adaptive protection algorithms based onCCVT transient error estimation or SIR, the degree of the transienterror resulting from CCVT, that is, the impedance calculation preci-sion, is estimated according to some indexes. Then, this degree isused to adjust the time delay of the protection adaptively. In thiscase, the minimum operation time under some fault conditionswill inevitably exceed 34 ms. In contrast, the new method is basedon ETPTL, which effectively reduces the transient error caused byCCVT and improve the operating speed by a series of technicalcountermeasures including restructuring the voltage at the faultpoint, virtual transfer method and R–L differential equation baseddistance relaying algorithm.

Table 2 provides part of typical simulations results. Where, SGFmeans single phase ground fault, PPF means phase-phase short-circuit fault, and TPF means three-phase short-circuit fault. Furthersimulation tests prove that the new method effectively reduces thetransient error caused by CCVT, within a 5% distance measuring er-ror at about 15 ms after fault occurrence, which is obviously supe-rior to various adaptive protection algorithms based on CCVTtransient error estimation or SIR.

Fault distance measuring error can be given by

error ¼ jD� lj=l ð5Þ

D is the actual fault distance measuring value and l is the realvalue of fault distance.

In addition, compared with the regular distance protectionalgorithm, which guarantees the distance measurement precisionby means of a long time delay, the operation speed of the newmethod is much faster.

In order to compare the simulation results between the pro-posed method and the method in [14], which is called as FPAA-based mho distance relay considering CCVT transient supervision,average operating times for different fault types, SIRs {5,15}, anddifferent fault locations {0,75,90,100}% have been shown in Table3. Where, ‘‘new’’ means the proposed method, and ‘‘fpaa’’ meansFPAA-based mho distance relay considering CCVT transient super-

Table 3Average operating times (ms) of the proposed method and the FPAA-based relay.

Ph–G Ph–Ph

SIR = 5 SIR = 15 SIR = 5 SIR = 15

New fpaa New fpaa New fpaa New fpaa

0 8 10 12 27 8 11 12 2675 10 17 15 28 10 19 15 3890 15 NO 25 NO 15 NO 25 NO

100 NO NO NO NO NO NO NO NO

NO: no operation.

vision. As seen, the proposed method is able to achieve fast operat-ing speed and higher accuracy.

4. Conclusions

Based on ETPTL, the reason of CCVT leading to the transientoverreach of distance relays is analyzed in this paper. It is pointedout that the transfer link of the voltage and current involved in thedistance protection calculation are not consistent. Therefore, thevoltage difference between the relay location and the fault pointas well as the current measured by the distance relay cannot com-ply with the model of the protected transmission line. To overcomeabove problem, a fast distance protection scheme that can be uti-lized to prevent the transient overreach caused by CCVT is put for-ward. The results of the simulation tests show that the newmethod can effectively reduce the transient error caused by CCVTless than ±5% at about 15 ms after fault occurrence, which is obvi-ously superior to various adaptive protection algorithms based onCCVT transient error estimation or SIR. Furthermore, comparedwith the conventional distance protection algorithms, the opera-tion speed of the new method is much faster.

Acknowledgments

This work was supported by the National Natural Science Foun-dation of China (51077061 and 50837002).

References

[1] Sadeghi Hadi. A novel method for adaptive distance protection of transmissionline connected to wind farms. Int J Electr Power Energy Syst2012;43(1):1376–82.

[2] Ghorbani Amir, Khederzadeh Mojtaba, Mozafari Babak. Impact of SVC on theprotection of transmission lines. Int J Electr Power Energy Syst2012;42(1):702–9.

[3] Al-Kandari Ahmad, Gilany Mahmoud, Madouh Jamal. An accurate techniquefor locating faults by distance relays. Int J Electr Power Energy Syst2011;33(3):477–84.

[4] Lin X, Li Z, Ke S, Gao Y. Theoretical fundamentals and implementation of novelself-adaptive distance protection resistant to power swings. IEEE Trans PowerDeliv 2010;25(3):1372–83.

[5] Ricardo Caneloi dos Santos a. Eduardo cesar senger, transmission lines distanceprotection using artificial neural networks. Int J Electr Power Energy Syst2011;33(3):721–30.

[6] Xia Jingde, Jiale Suonan, Song Guobing, Wang Li, He Shien, Liu Kai.Transmission line individual phase impedance and related pilot protection.Int J Electr Power Energy Syst 2011;33(9):1563–71.

[7] Marti JR, Linares LR, Dommel HW. Current transformers and coupling-capacitor voltage transformers in real-time simulations. IEEE Trans PowerDeliv 1997;12(1):164–8.

[8] Kezunovic M, Kojoric L, Skendzic V. Digital models of coupling capacitorvoltage transformers for protective relay transient studies. IEEE Trans PowerDeliv 1992;7(4):1927–35.

[9] Fernandes Jr D, Neves WLA, Vasconcelos JCA. Coupling capacitor voltagetransformer: a model for electromagnetic transient studies. Electr Power SystRes 2007;77(2):125–34.

[10] Tziouvaras DA, McLaren P, Alexander G. Mathematical models for current,voltage and coupling capacitor voltage transformers. IEEE Trans Power Deliv2000;15(1):62–72.

[11] Pajuelo E, Ramakrishna G, Sachdev MS. Strengths and limitations of a newphasor estimation technique to reduce CCVT impact in distance protection.Electr Power Syst Res 2010;80(4):417–25.

86 M. Wen et al. / Electrical Power and Energy Systems 52 (2013) 81–86

[12] Benteng He, Yiquan Li, Bo ZQ. An Adaptive Distance Relay Based on TransientError Estimation of ccvt. IEEE Trans Power Deliv 2006;21(4):1856–61.

[13] Kasztenny B, Sharples D, Asaro V, Pozzuoli M. Distance relays and capacitivevoltage transformers—balancing speed and transient overreach. GeneralElectric Company, GER-3986; 2000.

[14] Dadash Zadeh MR, Sidhu TS. FPAA-based mho distance relay considering CVTtransient supervision. IET Gen Trans Distrib 2009;3(7):616–27.

[15] Izykowski J, Kasztenny B. Dynamic compensation of capacitive voltagetransformers. IEEE Trans Power Deliv 1998;13(1):116–22.

[16] Wen Minghao, Chen Deshu, Yin Xianggen. Instantaneous value and equaltransfer processes-based current differential protection for long transmissionlines. IEEE Trans Power Deliv 2012;27(1):289–99.

[17] Minghao Wen. A new scheme of the protection based on the principle ofbalance of energy with virtual cvts. Proc CSEE 2007;27(24):11–6 [in Chinese].

[18] Elmore WA. Protective relaying theory and applications. 2nd ed. MarcelDekker Inc.; 2004.

[19] Ghorbani Amir, Mozafari Babak, Ranjbar Ali Mohammad. Digital distanceprotection of transmission lines in the presence of SSSC. Int J Electr PowerEnergy Syst 2012;43(1):712–9.

[20] Zadeh Hassan Khorashadi, Li Zuyi. Adaptive load blinder for distanceprotection. Int J Electr Power Energy Syst 2011;33(4):861–7.

[21] Bakara Ab Halim Abu, Yatimc Fazilah Mat, Yusofb Sallehuddin. Analysis ofoverload conditions in distance relay under severe system contingencies. Int JElectr Power Energy Syst 2010;32(5):345–50.