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Performance of Power Differential Relay With Adaptive Setting for Line Protection Abdel-Maksoud I. Taalab, Senior Member, IEEE, Hatem A. Darwish, and Eman S. Ahmed
Abstract—In this paper, proposed setting and response evaluations of power differential relay scheme for line protection are presented. Mathematical expressions describing the adaptive features of both active and reactive power settings are given. The union action of these two detectors is adopted to provide sensitive detection for high impedance internal faults and avoid maloperation for all power swings and external fault conditions. Response is computed for both active and reactive power detectors under different operation and fault conditions. The results corroborate the applicability and the immunity of the proposed relay scheme against the sampling misalignment and practical frequency drift. High sensitivity for high impedance internal faults is verified. Index Terms—Adaptive protection, high-impedance faults, line protection, power differential relay, relay setting.
I. INTRODUCTION
A
PPLICATION of differential concept to line protection is one of the new research areas, which attracted many engineers and relay manufacturers. Efficient application of this concept particularly with the current differential scheme reveals several problems, which postponed the expansion of this scheme in the field. These are the line charging current, errors in current transformers (CTs) and protection system, time delay of the communication channel, and synchronization of phase currents at both ends [1]–[4]. The later is a complicated issue to be overcome as both transformer errors and delay time can be marginally compensated. Two main concepts dealing with the issue of phasor synchronization for line differential protection have been reported. The first concept was concerned with the application of a global positioning system (GPS) satellite to measure phasor quantities with higher precision [5]. The second concept was concerned with the development of new algorithms operated on quantities that are partially or fully independent on current phasors [6]–[8]. Schemes based on the second concept are more practical as the GPS is a sophisticated system and may suffer interruption, which is not under the control of the power system protection engineer. These schemes are mainly the charge comparison [6], the based on composition of modal voltage and current measurements at both ends [7], and that employed the wavelet techniques [8]. Amongst these schemes, the charge comparison
Manuscript received May 25, 2005; revised January 30, 2006. Paper no. TPWRD-00306-2005. A.-M. I. Taalab and H. A. Darwish are with the Power System Protection Group (PSPG), Electrical Engineering Department, Faculty of Engineering, Menoufiya University, Shebin El-kom 32511, Egypt (e-mail:
[email protected];
[email protected]). E. S. Ahmed is with the Ministry of Electricity and Energy (MEE), Rural Electrification Authority, Cairo 1122, Egypt (e-mail:
[email protected]). Digital Object Identifier 10.1109/TPWRD.2006.877101
seems to be the most practical one, as it is inherently immune to the sampling misalignment. However, it depends totally on the current zero crossings, which may cause slow response under some fault conditions. In sympathy with these methods, a novel power differential concept has been recently proposed [9]. This concept is based on computing the active and reactive power loci during normal operation, switching, normal power swing, and internal and external faults. From these loci, discrimination of internal faults can be achieved. Determination of the appropriate setting and evaluation of the real-time operation are highly demanded as long as further realization of a power differential relay is concerned. In this paper, setting and real-time operation of the power differential relay used for line protection are presented. The appropriate expressions describing the thresholds for both active and reactive power detectors are given. The decision of these two detectors is ORed and tripping is generated in an adaptive manner. Sensitive detection for high impedance internal faults avoiding maloperation for all power swings and external fault conditions is verified. Response is computed for both detectors under different internal and external fault conditions considering possible frequency drifts. The results corroborate the applicability of the proposed scheme and its immunity to the sampling misalignment and power swings. II. POWER DIFFERENTIAL RELAY In this proposed power differential relay, the union action of the active and reactive power detectors is considered [9]. This provides a complement in addition to some overlapping as far as the type of fault, the range of fault resistance, and power angle swings are concerned. The concept of the power fault detection and the overall scheme can be described with the help of Figs. 1 and 2. With reference to Fig. 1, the current and voltage measured are fed to band-pass (BPF) filters tuned to the fundamental frequency. The filtered signals are sampled, multiplied, and the produced instantaneous power is transmitted to the remote end via a communication channel. The instantaneous power (indicated with subscript ) is computed for the active power at both transmission line ends on a sample-by-sample basis. The and are computed where and are the sending and receiving ends instantaneous power, respectively. Then, the corresponding average active power quantities and are computed over a complete cycle. However, in the reactive power algorithm, the instantaneous reactive and receiving ends is compower at the sending puted by multiplication of voltage sample, after being delayed
0885-8977/$20.00 © 2007 IEEE
TAALAB et al.: PERFORMANCE OF POWER DIFFERENTIAL RELAY WITH ADAPTIVE SETTING FOR LINE PROTECTION
Fig. 1. Active power difference and average extraction diagram for phase a.
Fig. 2. Block diagram of the proposed power fault detector for phase a.
by a quarter of a cycle, by the current sample at the same end. The instantaneous reactive power is computed at both ends on and a sample-by-sample basis. The difference average are computed over a complete reactive power through cycle for both ends in a similar manner to that for the active , , , power algorithm shown in Fig. 1. Values of are employed to feed the overall fault detector scheme and shown by Fig. 2. Details of this detector mathematics are given in [9]. With reference to Fig. 2, the output-tripping signal of the active power detector scheme is represented by the output of comparator 5. This signal is ORed with the output of the reactive power detector in conjunction with the 3-phase fault enable signal via 3-input OR2 gate. A similar fault detection scheme logic block diagram is used for the two other phases. As can be ’s measured for the other two phases are made availseen, able at the input of the detector dedicated to each phase in addi. This algorithm is made adaptive tion to the setting value by discrimination between fault and power swing conditions and also by blocking the reactive power detector for line-to-line (L-L) faults and enables it for other types of fault. The value of
Fig. 3.
1P
51
along with PS, an internal midline fault, and external fault loci.
is computed and compared with setting value . If the computed value is higher than the set level, a trip command is issued indicating a fault condition. However, if this computed value is less than the setting, a block signal is issued indicating a normal power swing. Determination of most appropriate set, , and ) ting expressions for this detector ( is quite interesting problem and will be discussed in the subsequent sections. Most of the results in the paper context will be given for 308 km of the 400-kV line as it is not mentioned otherwise. The electromagnetic transient program (EMTP) is employed in simulating these systems considering the distributed parameter model for the transmission line in order to account for the unsymmetrical fault analysis [9]. III. ACTIVE POWER DETECTOR SETTING CHARACTERISTICS The active power setting of the proposed detector should fulfill the maximum internal fault sensitivity and external fault stability under the probable worst conditions. The worst condition occurs with external solid single line-to-ground (SLG) fault at remote end and is given by the end of the solid straight line at of about (0.281 p.u. on a base value equal to the surge impedance loading of the line rated at 400 kV and 450 MW). The active power setting must be above this value as shown by Fig. 3. In Fig. 3, different load, power swing, and internal/external SLG fault conditions are given. Also, the setting characteristic must enclose the high impedance external fault locus, locus. On the other hand, the setwhich comes outside the ting should detect or come below the locus of the worst condition under an internal fault. This worst condition is obtained for the fault at the line midpoint, at which for different fault impedances, all internal SLG (not shown in Fig. 3). These loci fault loci are joined at almost follow the shape of the power swing. Therefore the shape of the setting characteristic is so chosen to be monotonic to these
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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 1, JANUARY 2007
loci or follows equation similar to the power swing equation. It is proposed that the setting of the differential power is represented by two segments. The first segment is expressed by the following equation:
(1) is the average differential power at power angle is the average through power at power angle . is the measured quantity of the average through active power at relay location. is a multiplier constant which at power angle determines the maximum value of and 180 . A value of 1.75 is adopted. This segment is plotted and given by the dashed curved line shown in Fig. 3. It can be concluded that a wide segment range of high impedance internal fault loci up to 400 can be detected or come above the threshold along the line for the range of from 0 to 180 except for a narrow zone around the line midpoint, the range of is terminated at about 1200 as shown in Fig. 3. The relay usually operates before reaches this value. The second segment is expressed by the equation where
.
for
(2)
is the power through multiplier, which determines the where . is set equal to 1.9. This limit of the horizontal setting of segment is plotted as a dashed straight line tangent to the first curved segment at “ ” and intersects the horizontal axis at “ ” as shown in Fig. 3. The active power detector Algorithm and begins with calculations of the average values as given by the flowchart of Fig. 4. The measured value of is compared with the value of , if it is less; is , computed from (1). However, for is computed from (2). If the measured value the value of of is greater than the obtained from (1) or (2), a is less than , a new trip signal is issued. However if cycle of calculation is started. It could be appreciated that the proposed active power relay algorithm allows the threshold to be , adaptive according to the values of the actual power flow , and maximum maximum power transferred capability; . power difference between the line ends; It is worth mentioning here that some transmission-line relays may operate for stable power swings for which the system should recover and remain stable. The magnitude of the swing center voltage (SCV) is related directly to ; the angle difference of the two sources. For example, if the measured magnitude of the SCV is half of the nominal value, then is 120 assuming equal source voltages and a homogeneous system. The absolute value of the SCV is at its maximum when the angle between the two sources is zero, and this value is at its minimum (or zero) when the angle is 180 . This property has been exploited so one can detect a power swing by looking at the rate of change of the swing center voltage. Alternatively, the electrical center from circuit theory is the point of the lowest absolute potential. This potential will de-
Fig. 4. Flowchart of the active power algorithm (P -detector).
crease as long as is increased. It will approach the zero level when is 180 . Regarding the system of Fig. 1, the electrical center is coincidently is the line midpoint as the sources are of identical parameters. Therefore, detection of the faults at this point will be an issue of any relaying system particularly at values beyond 120 [10], [11]. Efficient detection of faults at line midpoint is an exclusive feature of the proposed power differential relay. This is attributed to the union action of both active and reactive power components. When the active power difference is incapable of detecting these faults, reactive power detector is quite sensitive to them as outlined below. IV. REACTIVE POWER DETECTOR SETTING CHARACTERISTICS The reactive power setting of the proposed detector should come over all cases of external fault and power swings. Also, detect all cases of internal fault, which the active power setting is failed to detect. These cases namely are solid and low resistance (up to 1 ) internal SLG fault at line ends, solid SLG fault, and low resistance (from 0 to 3 ) around the line midpoint for all values of from 0 to 180 . Also, it should detect high SLG fault resistance above a power angle of 120 . In order to make the reactive power detector setting fulfill the above-mentioned conditions; the loci of the worst relevant cases are collected from the results of [9] and replotted on a semilog scale as shown in Fig. 5. It can be seen from Fig. 5 that an appropriate setting threshold should follow two straight-line segments (as shown by the dashed lines). The first line segment is given by the inclined . Where, point gives the intersection of this line of length line with the vertical axis. The point of this intersection is set to a value just above the transmission-line capacitive charging . MVAR However point is the intersection of the inclined line segat 2/3 of the ment with the reactive power swing locus . This line segment can be expressed by the following equation: (3)
TAALAB et al.: PERFORMANCE OF POWER DIFFERENTIAL RELAY WITH ADAPTIVE SETTING FOR LINE PROTECTION
Fig. 5.
1Q
53
along with reactive power swing and SLG fault loci.
where is a multiple of and is set to about 1.1. is the measured quantity of the average reactive power through at is the first segment slope determined from relay location.
Q
Fig. 6. Proposed flowchart for the reactive power algorithm ( -detector).
(4) where is the maximum of average of the reactive power , is the average difference, which occurs at . The of reactive power corresponding to two-thirds the is so chosen to avoid any intersection with all internal slope fault loci correspond to the line midpoint as shown in Fig. 5. The second line section is given by the dashed horizontal line, which intersects with the first line section at point . This line segment can be expressed by the following equation: (5) If , the active portion of the setting will be given , it will be governed by (5). by (3). However, if The reactive power detector algorithm is developed based on the average quantities of the difference and through reactive power similar to the active power algorithm. Flow chart is and . The algorithm started with the calculation of contains two comparators. In the first comparator, the measured is compared with the value of computed value of from (3). If is less than , a new cycle is started. If it is greater, a trip signal is issued. In the second comparator, is compared with the value of 2/3 the measured value of . If it is less, it is compared with the first comparator setting. However if it is greater than 2/3 , a trip signal is issued. A flowchart of this algorithm is given in Fig. 6. The block diagram of reactive power fault detection scheme is shown in Fig. 2 when comparator 5 is removed. The operation of the reactive power scheme is arranged to be blocked for L-L fault as well as for power swing conditions. However, it must be enabled for SLG and three-phase faults. Implementing this may demand two other comparators 3 and of the other two phases that is, 4 employing
and of phases and in conjunction with comparator of , respectively. This is shown in Fig. 2 with 2 of comparator 5 is removed. Blocking for L-L fault is provided because of the encroachment of the external L-L fault locus into the operation zone, which will appear as an internal fault. This occurs particularly at relatively high fault resistance. V. SETTING UNIVERSALITY The proposed active and reactive power setting universality were verified by studying the application to three different transmission line systems. These systems are namely 230 kV and 144.4 km, 400 kV and 308 km, and 500 kV and 244 km. The setting thresholds in conjunction with the internal and external SLG fault loci are plotted as given in Fig. 7(a) and (b) for the active and reactive power detectors, respectively. It can be seen that the active power setting threshold for each of the three-systems comes above the loci of the busbar external or internal solid SLG fault as shown in Fig. 7(a). Thus, -detector remains stable for external SLG fault and does not detect busbar solid internal SLG fault. Also, the sensitivity for detecting high impedance internal SLG fault is increased as the system voltage rating is increased. On the other hand the corresponding loci for the reactive power detector are shown in Fig. 7(b). It can be seen that the internal SLG fault loci for all ranges of power angle come above the reactive power setting thresholds and the external fault loci come under the corresponding reactive power setting threshold. Thus, -detector is stable for all external SLG fault and sensitive for internal SLG fault for the 3-systems. It can be seen that the solid busbar SLG external fault loci for the 3-transmission lines always come under the corresponding setting threshold loci with almost the same margin which verify the proposed setting universality.
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the setting parameters, a simplified procedure for setting the proposed power relay is needed, preferably in steps. , , and are constants and independent of the pro1) tected line parameters with values 1.75, 1.9, and 1.1, recan be computed when the comspectively. However, ponents of (4) are defined. can be approximately computed for the rated re2) ceiving and sending end voltage magnitudes ( and at ) as: , where the posi. tive-sequence transmission-line impedance is 3) However the maximum power differences is ob; , where tained when . Note that, , and are . absolute values, where can be approximately computed by 4) Similarly, . approximately, where 5) Also, and are the line positive-sequence inductive and capacitive reactance, respectively. approximately. 6) Finally, The aforementioned steps have been applied to the different transmission systems investigated in the paper and close matches to the setting thresholds of Fig. 7 have been obtained. Also, it is evident from 1–6 that the protection engineer can easily undergo these calculation for any transmission line. and can be replaced by Toward more simplifications, the rated phase voltage of the transmission line. Also, the scheme is inherently adaptive as it can easily accept etc., coming from changing different values of the line capability via compensation for example. Supervision can be provided from the switching status of the compensation capacitor. This increases the value added by the proposed relay to the area of adaptive computer relaying. VII. PERFORMANCE EVALUATION
Fig. 7. Setting threshold with different transmission system ratings. (a) P -detector and (b) Q-detector.
VI. STEP-BY-STEP SETTING OF THE PROPOSED RELAY In fact, the power swing loci may differ with the variations of loading level, disturbance conditions, generation size, and power system topology. Hence, achieving the aimed relay performance for these extraordinary condition considering and charts would ultimately imply better perthe formance during the typical power system swings. This is because the expected operating points will never deviate from the plotted loci. Also, this procedure would be more convincing for field engineer. Nevertheless, as it is not usually easy for the protection engineer to carry out a simulation study to determine
The performance of the power differential relay scheme with the proposed setting is intensively evaluated via real-time test cases. Around three thousands of different operating and fault cases are applied and the scheme is appropriately operated with sufficient discrimination margin. These cases cover the entire length of the line (seven locations), (13 values), fault inception values (30 values) conangles (0 and 90 ), and different sidering miscellaneous phase and earth fault conditions. Critical responses for active and reactive power detectors including internal and external fault cases with different power angle, frequency drifts and misalignment between signals at both ends followed by fault condition will be only addressed in the subsequent sections. A. Real-Time Response Under Fault Conditions The -detector response is computed for sudden application of solid external SLG fault at end S and the power angle . The result is recorded in conjunction with the proposed active power setting as shown in Fig. 8. It can be seen that the , which is shown by a solid line, remains below value of the setting threshold, which is shown by the dotted line. That is the detector remains stable for this condition. Unfortunately, for the internal solid SLG fault at the same end, the time response
TAALAB et al.: PERFORMANCE OF POWER DIFFERENTIAL RELAY WITH ADAPTIVE SETTING FOR LINE PROTECTION
Fig. 8.
P -detector response for solid SLG fault at end S and = 30
Fig. 9. Q-detector response for a solid SLG fault at end S and Q-detector and (b) fault current.
55
Fig. 10. P -detector response for SLG fault at end S of R
= 1 and = 30
.
Fig. 11. Q-detector response for SLG fault at end S of R
= 1 and = 30
.
.
= 30
. (a)
is identical to that of the external fault given by Fig. 8. This response indicates that the active power detector will not detect this type of fault. On the other hand, the -detector response for the above mentioned fault is shown in Fig. 9(a). However, Fig. 9(b) shows the corresponding fault currents measured at end S. It is evident from Fig. 9 that the -detector operates in about 7.5 ms for internal fault. The value of exceeds rapidly the threshold as shown by the upper solid line of Fig. 9(a). The power sliding window acquires few samples from the fault current and voltage to depict a significant change in the power term. Note that, the tripping signal can not be issued before one full cycle of confirmation. That is in order to avoid any transient impulses that
may appear in either active or reactive power computed values. However for external fault condition, the value of remains under the setting threshold by a large margin as shown by the lower solid line. The response of both detectors was examined also for low . The responses of both active fault resistance, e.g. (shown in Fig. 10) and reactive power (shown in Fig. 11) detectors are acting successfully in detecting this internal fault and stable for the external one. Response of the active power detector for high resistance fault of 400 can be appreciated with reference to the response of Fig. 12. This shows the remarkable sensitivity of the proposed scheme for the detection of the high-impedance fault. In order to emphasize the particular issue of relay sensitivity, result depicted by Fig. 10 can be compared with that one of Fig. 8. With reference to Fig. 8, the relay is stable for both external and internal solid faults at end S. This is attributed to that and do not vary whether the during these faults fault at S is internal or external. So, the relay discrimination is failed. However, if the fault occurs through resistance (even near 1.0 ) the relay discrimination is improved as shown in Fig. 10. The values of is increased from zero at to for nonzero . Definitely, the sensitivity level for these faults will be improved as the system rated voltage is increased. For the SLG fault at the midpoint of the line with power angle of 112 , the -detector can not detect this high resistance fault
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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 1, JANUARY 2007
Fig. 12.
= 30
P -detector response for the SLG fault at end S of R = 400 and
Fig. 14. Q-detector response for SLG fault at midline for R = 110 .
= 1600 and
.
Fig. 13. P - and Q-detectors for SLG fault at midline for R = 112 .
= 400 and
(400 ) as shown in Fig. 13. Fortunately, the -detector is sensitive for this type of internal faults. A substantial reduction occurred in the reactive power setting threshold (given by dashed , which is shown by the solid line) below the value of , which line. This reduction is mainly due to reduction of constitutes the adaptive variable term of the proposed setting of (3). It should be emphasized that the reactive power detector has a remarkable sensitivity since it is capable of detecting higher values of fault resistance (0–400 ) covering the entire length of the line including the midpoint for range of 0 –180 . Higher fault resistances can be also detected as shown in Fig. 14 for and for a fault at the line midpoint. In the contrary, the current differential relay detects the SLG up to 150 as previously illustrated in [9] for faults with . Lower sensitivities are expected for higher values of . Complete blindness of current relays, in general, is expected regardless the value of . for faults at the midline at B. Real-Time Response Under Frequency Drifts The responses of the active and reactive power detector are examined under frequency variation by 10% of nominal operating frequency followed by a fault condition. The response for reduction of frequency to 45 Hz followed by a solid external SLG fault at end S after 0.08 s are plotted as shown in Figs. 15 and 16 for active and reactive power detecfor the tors, respectively. It can be seen that the value of
Fig. 15. P -detector for f = 30 .
Fig. 16. Q-detector for f = 30 .
= 45 Hz with sudden external solid SLG fault at
= 45 Hz and sudden external solid SLG fault at
first swing after fault inception exceeds the threshold for a period of about 10 ms. However, the rest of oscillatory response comes under the setting threshold as shown in Fig. 15. of On the other hand, the corresponding response for the reactive power detector remains stable with sufficient margin. to 55 Hz The corresponding response for increasing is shown in Figs. 17 and 18. It can be seen that active and reactive power detectors remain stable under this relatively large variance ( 10%) in frequency considering trip decision confirmation of one complete cycle (20 ms). C. Real-Time Response Under Sampling Misalignment Figs. 19 and 20 show the active and reactive power detector responses for an 1/4 of cycle (8-samples) misalignment between
TAALAB et al.: PERFORMANCE OF POWER DIFFERENTIAL RELAY WITH ADAPTIVE SETTING FOR LINE PROTECTION
Fig. 17.
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P -detector for f = 55 Hz and sudden external solid SLG fault at
= 30 .
Fig. 20. Q-detector response under misalignment followed by an external solid SLG fault at end S and = 30 .
Fig. 18. Q-detector for f = 55 Hz and sudden external solid SLG fault at = 306 . Fig. 21. Q-detector response during line energization and = 30 .
Fig. 19. P -detector response under misalignment followed by an external solid SLG fault at end S and = 30 . Fig. 22. P -detector response for line energization with = 30 .
the corresponding signals at both ends followed by an external SLG fault at end S after 0.16 s. It can be seen in both figures that, and for a period of one a temporary increase in cycle (20 ms) due to this misalignment. On the other hand, after fault occurrence a relatively high increase (compared to Figs. 8 and occurred particularly for the and 9) in both first swing post fault inception. However, both detectors remain and come below stable since the magnitude of both the corresponding setting threshold with clear margin. D. Real-Time Response Under Line Energization The response for energizing the line from one end while the other end is open is shown in Figs. 21 and 22 for and
, respectively. This condition yields the worst condition as far as line energization is concerned. It can be seen that both active and reactive power detectors remain stable. Also energizing the line on internal and external SLG fault at end S yields the response of reactive power detector as shown in Fig. 23. It can be seen that the fault is detected by the reactive power detector within 10 ms. The active power detector will not detect this busbar fault since the voltage drops to zero. However, memory action with the reactive power detector supports the of about 7.4 p.u. for an internal fault voltage and yields and 0.1 p.u. for an external fault.
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Fig. 23.
Q-detector response during line energization on SLG faults at end S. VIII. CONCLUSION
In this paper, setting and real-time operation of the power differential relay scheme for line protection have been presented. The appropriate expressions describing the thresholds for both active and reactive power detectors are proposed, validated, and examined. The decision of these two detectors is ORed and tripping is generated in an adaptive manner. Sensitive operation for high-impedance internal fault avoiding maloperation for all power swings and external fault conditions has been verified. The application universality of the proposed setting for different transmission systems has been justified. The proposed relay real-time response is computed for both detectors under line energization, different internal and external faults considering possible frequency drifts. The results corroborate the applicability of the proposed relay as it is perfectly immune to the sampling misalignment, small frequency excursions, and transients associated with line energization. Hardware implementation of a DSP-based the power differential relay strengthened with analog/digital filters, which are directed to increase the relay stability against dc offset, harmonics, frequency drifts, and different system power swing conditions are being carried out and results will be published shortly.
REFERENCES [1] C. R. Mason, The Art and Science of Protective Relaying. New York: Wiley, 1984. [2] GE Power Management, “L90 Line Differential Relay,” UR Series Instruction Manual 1601-0081-B2 (GEK 106231) 2000. [3] W. S. Kwong, M. J. Clayton, and A. Newbould, “A microprocessor based current different relay for use with digital communication systems,” in Proc. 3rd Int. Conf. Developments in Power System Protection, Apr. 1985, pp. 65–69. [4] R. K. Aggarwal and A. T. Johns, “A differential line protection scheme for power systems based on composite voltage and current measurements,” IEEE Trans. Power Del., vol. 4, no. 3, pp. 1595–1602, Jul. 1989.
[5] IEEE Committee Rep., “Synchronized sampling and phasors measurements for relaying and control,” IEEE Trans. Power Del., vol. 9, no. 1, pp. 442–452, Jan. 1994. [6] L. J. Ernst, W. L. Hinman, D. H. Quam, and J. S. Thorp, “Charge comparison protection of transmission lines—relaying concepts,” IEEE Trans. Power Del., vol. 7, no. 4, pp. 1835–1852, Oct. 1992. [7] H. Y. Li, E. P. Southern, P. A. Crossley, S. Potts, S. D. A. Pickering, B. R. J. Caunce, and G. C. Weller, “A new type of differential feeder protection relay using the global positioning system for data synchronization,” IEEE Trans. Power Del., vol. 12, no. 3, pp. 1090–1099, Jul. 1997. [8] C. K. Wong, C. W. Lam, K. C. Lei, C. S. Lei, and Y. D. Han, “Novel wavelet approach to current differential pilot relay protection,” IEEE Trans. Power Del., vol. 18, no. 1, pp. 20–25, Jan. 2003. [9] H. A. Darwish, A. I. Taalab, and E. S. Ahmed, “Investigation of power differential concept for line protection,” IEEE Trans. Power Del., vol. 20, no. 2, pp. 617–624, Apr. 2005. [10] Power System Relaying Committee, WG D6, “Power swing and out-of-step consideration on transmission lines,” Power System Relaying Committee (PSRC) Rep., IEEE-PES Issued on the Published Reports Homepage on, Jul. 19, 2005. [11] S. A. Soman, T. B. Nguyen, M. A. Pai, and R. Vaidyanathan, “Analysis of angle stability problems: a transmission protection systems perspective,” IEEE Trans. Power Del., vol. 19, no. 3, pp. 1024–1033, Jul. 2004. Abdel-Maksoud I. Taalab (M’99–SM’03) received the B.Sc degree in electrical engineering from Menoufiya University, Menoufiya, Egypt, in 1969, and the M.Sc. and Ph.D degrees from Manchester University (UMIST), Manchester, U.K., in 1978, and 1982, respectively. In the same year of his graduation, he was appointed Assistant Professor at the Menoufiya University. He joined GEC Company in 1982. He is now a Full Professor with the Department of Electrical Engineering, Faculty of Engineering, and Vice Dean of the Desert Environment Institute, Menoufiya University. His interests are in HVDC transmission systems, power system protection, and power-electronics applications.
Hatem A. Darwish was born in Quesna, Egypt, in 1966. He received the B.Sc. (Hons.), M.Sc., and Ph.D. degrees in electrical engineering from Menoufiya University, Menoufiya, in 1988, 1992, and 1996, respectively, and the Ph.D. degree from Memorial University of Newfoundland (MUN), St. John’s, NF, Canada, in 1996, based on joint supervision with Menoufiya University. He has been involved in several pilot projects for the Egyptian industry for the design and implementation of numerical relays, SCADA, fault location in medium-voltage (MV) feeders, distribution-management systems, protection training packages, and relay coordination. He is currently an Associate Professor. His interests are in digital protection, signal processing, system automation, EMTP simulation, ac/dc power system transients, and switchgear.
Eman S. Ahmed was born in Quesna, Egypt, on September 11, 1966. She received the B.Sc. and M.Sc degrees in electrical engineering from Menoufiya University, Menoufiya, Egypt, in 1988 and 2004, respectively, and is currently pursuing the Ph.D. degree in line protection. Currently, she is a Protection Engineer with the Ministry of Electricity and Energy, Rural Electrification Authority, Cairo, Egypt, where she has been since 1989.
