A New Fault Locator for Three-Terminal Transmission Lines Using Two-Terminal Synchronized Voltage and Current Phasors

Transcription

1 452 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 17, NO. 2, APRIL 2002 A New Fault Locator for Three-Terminal Transmission Lines Using Two-Terminal Synchronized Voltage and Current Phasors Ying-Hong Lin, Chih-Wen Liu, Member, IEEE, and Chi-Shan Yu Abstract With the advent of the high synchronization accuracy of modern phasor measurement units (PMUs), a new approach for accurately locating faults on three-terminal lines is proposed. Using the data measured from two terminals of three-terminal lines, the proposed technique can provide an extremely accurate fault location. An EMTP/ATP simulator is used to demonstrate the performance of the proposed fault locator. The simulation results show that the accuracy of fault location is very high under various fault resistance, fault locations, prefault loading conditions, source impedance and fault types. Index Terms Fault locator, phasor measurement units (PMUs), three-terminal lines. I. INTRODUCTION THE DEVELOPMENT of fault location techniques is very important, especially for the long lines in rough terrain, for reducing the crew repair expense and speeding up the restoration of service for power utilities. In the past two decades, many algorithms have been developed [1] [9]. The majority of published work is concerned with developing techniques for fault location on two-terminal lines [1] [7]. However, until recently, relatively little work has been done in the development of fault location technique for three-terminal lines [8], [9]. In the past few years, phasor measurement units (PMUs) have been rapidly developed and the associated standards have been made in 1995 [10]. The PMUs are especially suitable for the implementation of the fault locators due to their high synchronization. In our previous papers [6], [7], a PMU-based approach for fault location on two-terminal lines and the practical implementation of PMU have been proposed. Such an approach forms the basis of this work. Owing to the dispute on the right of way, some two-terminal transmission lines tapped with a source of generation via a new tapping line have been existing at the Taiwan power system. This fact cannot only drastically affect the degree of accuracy of the fault locator for the original two-terminal lines, but also expose the new tapping lines to be out of protection. So, the demand and importance of developing a fault locator for such three-terminal lines has increased. From the past literatures [8], [9], all of the proposed fault location algorithms applied to three-terminal lines utilize the measurements from all of three terminals. For example, Aggarwal et al. [8] utilized the prefault measurements that are available at three-terminals to estimate the synchronization errors among the measured data. These error quantities were utilized to correct the synchronization error of post-fault measurements and then the corrected data can be used to calculate the fault location. One drawback of such an approach is that their implementation cost is high since the proposed approach needs to install three data recorders. Besides, it is hard to perform a data synchronization procedure among data recorders and thereby inevitably increases the computation burden of the host computer significantly. Using the iterative method, Girgis et al. [9] resolved the unknown synchronization errors and obtain the fault location. However, the line model employed in [9] neglects the shunt capacitance. The paper cannot really reflect the nature of transmission lines and will further deteriorate the accuracy of the fault location. To cope with the mentioned problems, a new technique is proposed. The proposed technique uses the same configuration as fault locator for two-terminal lines [6], [7], i.e., just using two PMUs equipped at two ends of transmission lines and is capable of precisely locating faults independent of faults occurring on any leg of three-terminal lines. The proposed technique not only possesses the merit of less cost, but also utilizes distributed parameter model of lines to approach the reality of the transmission lines. To explain the concepts, the paper is organized into five sections. The first of which is the introduction. In Section II, descriptions of overall system configuration of PMU-based fault locator for three-terminal lines are presented. In Section III, a brief review of our previous proposed algorithms for two terminal lines is introduced. Then, an extension to three-terminal lines is presented. The algorithm for three-terminal lines will be divided into two steps: the first step is to identify the faulted leg. The second step is to locate a fault on the faulted leg. The evaluation of the proposed algorithm is presented in Section IV. Finally, the conclusion is given in Section V. Manuscript received August 29, Y.-H. Lin and C.-W. Liu are with the Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, R.O.C. C.-S. Yu is with the Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, R.O.C., and also with the Department of Electrical Engineering, Private Kuang-Wu Institute of Technology, Taipei, Taiwan, R.O.C. Publisher Item Identifier S (01) II. OVERALL SYSTEM CONFIGURATION The proposed algorithm combined with PMUs and communication links forms the fault locator system. The overall system configuration of the PMU-based fault locator for three-terminal /02$ IEEE

2 LIN et al.: NEW FAULT LOCATOR FOR THREE-TERMINAL TRANSMISSION LINES 453 Fig. 2. Transmission lines. Fig. 1. Overall system configuration of the proposed fault locator. transmission lines is shown in Fig. 1. For the clear explanation of the proposed approach, the three-terminal line will be divided into,, and. The lengths of these line segments are,, and, respectively. The three-terminal transmission line is originally composed of and, and the original line is labeled as. The outsides of are replaced by Thevenin s equivalence. Line is the tapping line. and represent the voltage source and source impedance of the source of generation, respectively. The PMUs are installed at both ends of the original transmission line to synchronously compute three-phase voltage and current phasors. There are two important features in the installed PMUs. One is a synchronized clock generator named the global synchronized clock generator (GSCG) [7] which has been built in PMUs. The GSCG, whose frequency shift and synchronization error can be respectively controlled well within 0.1 PPM and 1 s, provides an extremely accurate synchronized clock for data sampling. The other is the brand-new developed filtering technique named the smart discrete Fourier transform (SDFT) [11] that can extract the fundamental phasors from sampling data under various system operation situations. The performance of PMU-GSCG unit has been on-line demonstrated very well in the 161 kv substations of the Taiwan Power system [7]. These facts guarantee that the proposed fault locator performs the relaying task under synchronization configuration. The principle of the proposed algorithm is outlined as follows. After the fault occurs, the prefault and postfault synchronized phasors will be transmitted to the central computer via communication channels. The proposed algorithm will be performed at the central computer. These phasors are first transformed by symmetrical transformation to decouple the coupling effect among interphases. Then the superimposed positive-sequence components can be extracted by the application of the principle of superposition. The principle of superposition is presented at Appendix A. The fault location for three-terminal lines will be divided into two steps. The first step is to identify the faulted leg. At this stage, the superimposed positive-sequence quantities are used as input to the subroutine for identifying the faulted leg. The second step is to locate a fault on a specific faulted leg. In the second step, it should be noted that two different quantities, superimposed positive-sequence quantities and postfault positive-sequence quantities, will be adopted for locating a fault on a different faulted leg. The superimposed quantities will be used when a fault occurs on or. The postfault quantities are adopted when a fault occurs on. When a fault occurs on, it is essential to estimate the equivalent source impedance outside the line first. After the source impedance is known, the currents flowing from tapping line into the tap point can be estimated by means of measured phasors at terminal. Then, the previous proposed algorithm [6] will be applied by taking the effect of infeed currents into account. When a fault occurs on the, the similar process can be applied. When a fault occurs on the tapping line, it is essential to estimate the voltage source under the timing reference of PMUs by means of prefault measured phasors. After these have been accomplished, an exact fault location will be computed by means of the use of postfault measured data. III. BASIC PRINCIPLES A. Review of the Previously Proposed Fault Location Algorithm for Two-Terminal Lines Initially, consider the transposed transmission lines shown in Fig. 2 under sinusoidally steady state with angle frequency. The following parameter matrices, including series impedance matrix and shunt admittance matrix, characterize the considered transmission line. and denote the self and mutual series impedance per unit length, respectively, and and denote the self and mutual shunt admittance per unit length. The voltages and currents at a

3 454 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 17, NO. 2, APRIL 2002 distance (1). km away from the receiving end are related through (1) Both and are 3 1 vectors. The symmetrical components are adopted to resolve the coupling effect among interphases. The transformation matrix is shown as the following: Fig. 3. lines. Superimposed representation of faulted two-terminal transmission (2) is equal to Then, the coupling three-phase quantities can be decoupled into three independent symmetrical components as shown in (3). Fig. 4. Superimposed representation of faulted three-terminal lines. the subscripts 0, 1, and 2 denote zero-, positive- and negative-sequence components, respectively. Substituting (2) and (3) into (1) gives the following sequence equations: and are the sequence impedance and admittance matrices, respectively. and are all diagonal matrices, and the diagonal entries of matrices and are (,, ) and (,, ), respectively. Thus, the solution of (4) can be written as (5) the subscript denotes 0, 1, and 2 sequence variables, denotes the characteristic impedance, and is the propagation constant. Meanwhile, the constants and can be determined by voltages and currents measured at both ends of the lines. Since the positive sequence component always appears in all types of fault event, it is convenient that all of the quantities without specially declaring denote the positive sequence components through the remainder of this paper. Consider that a fault occurs on transmission lines and the superimposed representation of the faulted lines is shown in Fig. 3. Since the voltage at fault point expressed in terms of two data sets (, ) and (, ) are identical, the two-terminal approach proposed by our previous paper [6] can estimate the fault location away from the receiving end by (6). (3) (4) (6) (7), superimposed voltage phasors at both ends of the lines;, superimposed current phasors at both ends of the lines;, propagation constant and characteristic impedance, respectively; length of the transmission line. Moreover, it is remarkable that, for untransposed lines, one can also find the transformation matrix to transform the coupled phase quantities to decoupled modal quantities with eigenvalue/eigenvector theory [12]. Thus, (6) can still also be used for untransposed lines. B. Fault Location for Three-Terminal Lines The proposed algorithmfor three-terminal linesshown in Fig. 1 using two-terminal synchronized phasors is presented in this section. The superimposed representation of faulted three-terminal lines is shown in Fig. 4. The proposed algorithm will be divided into two steps: the first step is to identify the faulted leg and the second step is to locate a fault on a specific faulted leg. 1) First Step: Faulted Leg Identification: The first step of the proposed algorithm is to identify the faulted leg. This task can be achieved by comparing the real part of with. represents the distance of the tap point away from the receiving end. The denotes a computed fault location under the situation that we intentionally regard the original lines as two-terminal lines without being tapped with a source of generation. The is computed by means of substituting the measured superimposed data ( and ) and ( and ) illustrated in Fig. 4 into (6). The criteria of the faulted leg identification are described as follows. If, then the faulted leg is selected as. If, then the faulted leg is selected as. If, then the faulted leg is selected as. Here, denotes the real part of a complex number. Moreover, the detailed proof of the above faulted leg identification is given in Appendix B. (8)

4 LIN et al.: NEW FAULT LOCATOR FOR THREE-TERMINAL TRANSMISSION LINES 455 2) Second Step: Fault Location Algorithm: a) Fault Occurs on : After identifying the faulted leg, the fault location can be determined by utilizing the algorithm suitable to a specific faulted leg. At first, consider a fault occurring on and its superimposed representation is shown in Fig. 4. The computation of a fault location away from the receiving end can be treated as a fault location on two-terminal lines. Fault location can be easily obtained by substituting ( and ), ( and ) and line length into (6). The data ( and ) are the measurements from PMU_B installed at receiving end. can be obtained from measured data ( and ) and be expressed as (9) and can be expressed as (10) is a function derived from the application of current division theory. Thus, the fault location can be obtained by the following equation: (11) (12) Fig. 5. Fault occurs on line L. c) Fault Occurs on : Locating a fault on is based on an assumed condition that the fault types are known. Some practical fault type classification schemes can be found in [13]. The procedure of fault location on will be divided into two steps. The first is to estimate the internal voltage source. This can be achieved by (15). (15) and are the prefault voltage and current at terminal. These can be calculated by means of the prefault measurements (, ) and (, ). Once the is determined, the fault location on can be illustrated in Fig. 5. We can utilize,, and the assumption that fault impedance is purely resistive to estimate the fault location away from tap point. The is the postfault voltage at tap point and is the postfault current flowing from tap point into lines. Both of and can be calculated by means of the postfault measured data (, ) and (, ). The constraints for three common types of fault are characterized by (16) (18), respectively. Single Phase to Ground Fault: (13) is the current flowing from into the tap point. It can be represented as the following: Phase-to-Phase Fault: (16) (14). b) Fault Occurs on : When the fault occurs on, the computation of fault location away from the sending end can be treated as the fault location on two-terminal lines. We can intentionally substitute the following relationships into (11). Then, the fault location away from the sending end can be easily obtained. The fault location with respect to the receiving end can be computed from. Three Phase Balance Fault: (17) (18) denotes the post-fault voltage at the fault point, denotes the post-fault current flowing through the fault resistance and the subscripts, 0, 1, and 2, denote zero-, positive-, negative-sequence components, respectively. denotes the imaginary part. Moreover, an iterative secant method was used to solve the unknown fault location. C. Estimation of Equivalent Source Impedance Due to the time-varying property of equivalent source impedance, and shown in Fig. 4, it is essential to accurately estimate source impedances when the fault occurs. Such a procedure can overcome the uncertainty of equivalent source impedance and increase the accuracy of degree of fault location. According to the principle of superposition, the equivalent voltage sources and are disabled on the

5 456 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 17, NO. 2, APRIL 2002 TABLE I SIMULATION RESULTS (FAULT OCCURS ON L) superimposed circuit. Thus, the source impedances can be given, respectively, by the following equations: (19) (20) TABLE II SIMULATION RESULTS (FAULT OCCURS ON L ) IV. PERFORMANCE EVALUATION A. Simulation Example A simulation system shown in Fig. 1 is selected to verify the accuracy of the proposed algorithms. The parameters of the simulation system are System voltage: 161 (kv) System frequency: 60 (Hz) Transmission lines parameters: In this work, an EMTP/ATP simulator is adopted and the total time of simulation is (sec). The fault occurs at the fourth cycle after the beginning of simulation. The data are sampled at a sampling rate of 3.84 khz. The error of locating fault is measured as Error Actual Fault Location Estimated Fault Location The Length of Line (21) B. Simulation Results and Discussion Simulation results will be shown to evaluate the performance of the proposed algorithm. First, the proposed algorithm is evaluated when a fault occurs on either line or tapping line. The post-fault data used to compute the fault location is three cycles after fault occurring. Table I shows the results of fault location under various fault types, fault resistance and fault locations when fault occurs on line. Table II shows those when fault occurs on line. The sign # beside each fault location error in Tables I and II denotes that the faulted leg is identified correctly. Simulation results on Table I reveal that 1) For various fault types, the maximum variation of fault location errors caused by change of actual fault locations is 0.27%. This denotes that the proposed algorithm is almost not affected by the locations of faults. 2) For various fault locations, the maximum variation of fault location errors caused by different fault types is 0.239%. This shows that the degree of accuracy of proposed approach is nearly independent to fault types. 3) The final observation is that the fault resistance has little effect on the accuracy of the proposed approach. From the simulation results on Table I, the average error of fault location is 0.077% and maximum error is 0.28%. Since the distance between two towers is 0.3 km in the Taiwan power system, such a degree of accuracy meets the need. The average error of fault location estimation on is 0.17% and maximum error is 0.471% under all tested cases. There are two primary reasons that the fault location error on is greater than that on. The first is that we take shunt capacitance in transmission lines into account and such a complex model of lines reduces the strength of constraints for iterative calculation. The second is that the procedure of estimating the internal voltage source will also incur the error on fault location. The proposed algorithm is also evaluated with the variation of variable parameters like the equivalent source impedance, pre-

6 LIN et al.: NEW FAULT LOCATOR FOR THREE-TERMINAL TRANSMISSION LINES 457 TABLE III SIMULATION RESULTS UNDER SOURCE IMPEDANCE VARIATION TABLE V SIMULATION RESULTS UNDER ERRORS OF SETTING OF Z TABLE IV SIMULATION RESULTS UNDER DIFFERENT PREFAULT LOADING CONDITIONS fault loading conditions and source impedance of the source of generation. These studies will evaluate the robustness of the proposed approach. The first is to evaluate the effects on fault location caused by variations of equivalent source impedance. In the simulations, we intentionally varied the equivalent source impedance ( and ) from 0.2 to 5 times of original setting values. Such a range of variation is enough to cover the change of equivalent source impedance outside the line. Table III shows the simulation results. For various fault locations, the maximum variation of fault location errors caused by change of equivalent source impedance is 0.142%. Such a result denotes that the proposed algorithm is able to trace the change of the equivalent source impedance and make the accuracy of fault location almost independent of change of those outside the lines. Table IV shows the simulation results under different prefault loading conditions. These are represented in terms of phase angle difference between and. The results of simulation show that prefault loading conditions have little effect on the degree of accuracy of the proposed algorithm. All the simulation results described above are based on that the setting value of source impedance is exactly accurate. In practice, the setting value of will possess a certain error caused by measurement error of, different operation environments and the aging of coils. Therefore, it is necessary to study the sensitivity of the proposed algorithm versus the setting error of source impedance. We intentionally varied the source impedance from 20% to 20% of setting values. Table V presents the simulation results. According to simulation results, the average error caused by 20% variation of source impedance is approximately equal to % under the tested cases. V. CONCLUSION Nowadays, new rights of way for transmission lines are difficult to obtain. In some cases, tapping new lines to original transmission lines is the only reasonable solution. In this paper, a new fault location technique applied to such three-terminal configuration is proposed and the proposed technique just utilizes two PMUs on both ends of the original transmission lines. The proposed scheme not only possesses the economical advantage comparing to traditional techniques, but also retains the original two-terminal relaying configuration when the system extends to three-terminal configuration. The simulation results show that the accuracy of fault location is very high under the tested situations that include different various fault resistance, fault locations, prefault loading conditions, various source impedance and various fault types. APPENDIX A PRINCIPLE OF SUPERPOSITION The principle of superposition in the linear network theory separates a post-fault network into the prefault network and the superimposed network shown in Fig. 6. The relationship among postfault, prefault, and superimposed quantities can be expressed as follows: (A.1) (A.2) (A.3) (A.4) APPENDIX B PROOF OF THE CRITERIA OF FAULTED LEG IDENTIFICATION For simplicity, the shunt capacitance on the transmission line is neglected in the following derivation. Note that all of the phasors presented in Figs. 7 9 are superimposed quantities. At first, let us consider a fault occurring on the transmission line shown in Fig. 7. The voltage at the fault point can be expressed as the following: (A.5) line impedance per unit length; length of the transmission line ; fault location. After some algebraic manipulation, we can obtain the fault location away from the receiving end as the following: (A.6)

7 458 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 17, NO. 2, APRIL 2002 Case 1: Consider a fault occurring on a transmission line tapped with a source of generation shown in Fig. 8. It is assumed that the fault occurs on the left-hand side of tap point. Initially, the transmission line is intentionally regarded as lines without being tapped with a source of generation. Equation (A.6) will yield a pseudo fault location. Then, the and will be represented as follows: (A.7) (A.8) the is the voltage at pseudo fault location and is the length of line. Moreover, according to the Fig. 8, the and are also expressed as follows: (A.9) Fig. 6. The principle of superposition. (A.10) is the length of the line, is the actual fault location and is the voltage at the actual fault location. Arranging (A.7) (A.10), one can obtain the following equation: Arranging (A.11), we have (A.11) Fig. 7. The superimposed network under the condition that fault occurs on transmission lines without tapping lines. (A.12) Taking the real parts of both sides of (A.12) and manipulating them, one can obtain (A.13) Fig. 8. Superimposed network under the condition that fault occurs on the left-hand side of tap point. denotes the real part of a complex number. Defining the following relationship: (A.14) Based on the assumption that the source impedance (, and ) and the transmission line are highly inductive, the phase differences between each other of, and are less then 90. Then (A.15) Fig. 9. The superimposed network under the condition that fault occurs on the tapping line L. The proof of criteria for faulted leg identification is given in the following. Criterion 1: If, then the fault is on the right-hand side of tap point. Proof: We prove this criterion by a contradiction, that is, if the fault is not on the right-hand side of tap point, then. denotes magnitude of a complex number, and superscript denotes the conjugate of that. Substituting the result of (A.15) into (A.13), one can obtain (A.16) Since, then (A.17) Case 2: Consider a fault occurring on the tapping line shown in Fig. 9. According to the principle of deriving (A.6),

8 LIN et al.: NEW FAULT LOCATOR FOR THREE-TERMINAL TRANSMISSION LINES 459 the must be a real number and equal to. So, one can obtain (A.18) The combination of the results in cases 1 and 2 give the proof. Criterion 2: If, then the fault is on the left-hand side of tap point. Proof: The criterion is proved by a similar method described above. So, the proof is omitted. Criterion 3: If, then the fault is on the tapping line Proof: From the results of criterion 1 and 2, it is obvious that the criterion 3 is true. ACKNOWLEDGMENT The authors would like to thank Dr. J.-A. Jiang for reading the manuscript and making a number of helpful suggestions. REFERENCES [1] A. T. Johns and S. Jamali, Accurate fault location technique for power transmission lines, Proc. Inst. Elect. Eng. C, vol. 137, no. 6, pp , Nov [2] M. Sachdev and R. Agarwal, A technique for estimating transmission line fault location from digital impedance relay measurement, IEEE Trans. Power Delivery, vol. 3, pp , Jan [3] T. T. Takagi, et al., Development of a new fault locator using the oneterminal voltage and current data, IEEE Trans. Power App. Syst., vol. PAS-101, pp , Aug [4] L. Erikson, M. Saha, and G. D. Rockfeller, An accurate fault locator with compensation for apparent reactance in the fault resistance resulting from remote-end infeed, IEEE Trans. Power App. Syst., vol. PAS-104, pp , Feb [5] D. J. Lawrence, L. Z. Cabeza, and L. T. Hochberg, Development of an advanced transmission line fault location system Part II: Algorithm development and simulation, IEEE Trans. Power Delivery, vol. 7, pp , Oct [6] J.-A. Jiang, J.-Z. Yang, Y.-H. Lin, C.-W. Liu, and J.-C. Ma, An adaptive PMU based fault detection/location technique for transmission lines Part I: Theory and algorithms, IEEE Trans. Power Delivery, vol. 15, pp , Apr [7] J.-A. Jiang, Y.-H. Lin, J.-Z. Yang, T.-M. Too, and C.-W. Liu, An adaptive PMU based fault detection/location technique for transmission lines Part II: PMU implementation and performance evaluations, IEEE Trans. Power Delivery, vol. 15, pp , Oct [8] R. K. Aggarwal, D. V. Coury, A. T. Johns, and A. Kalam, A practical approach to accurate fault location on extra high voltage teed feeders, IEEE Trans. Power Delivery, vol. 8, pp , July [9] A. A. Girgis, D. G. Hart, and W. Peterson, A new fault location technique for two and three terminal lines, IEEE Trans. Power Delivery, vol. 7, pp , Jan [10] IEEE Standard for Synchrophasors for Power System, IEEE Std , May [11] J.-Z. Yang and C.-W. Liu, A precise calculation of power frequency and phasor, IEEE Trans. Power Delivery, vol. 15, pp , Apr [12] H. W. Dommel, EMTP Theory Book. Vancouver, BC: Microtran Power Syst. Anal. Corp., May 1992, pp [13] A. G. Phadke and J. S. Thorp, Computer Relaying for Power Systems. New York: Wiley, 1988, pp Ying-Hong Lin was born in Taipei, Taiwan, R.O.C., in He received the B.S. degree in electrical engineering from Taiwan University of Technology, Taipei, Taiwan, R.O.C., and the M.S. degree from National Taiwan University (NTU), Taipei, in 1995 and 1999, respectively. Currently, he is pursuing the Ph.D. degree in electrical engineering at NTU. His current research interests include the application of GPS and PMU in power systems. Chih-Wen Liu (M 94) was born in Taiwan, R.O.C., in He received the B.S. degree in electrical engineering from National Taiwan University (NTU), Taipei, Taiwan, and the M.S. and Ph.D. degrees in electrical engineering from Cornell University, Ithaca, NY, in 1987, 1992, and 1994, respectively. Since 1994, he has been with NTU, he is Associate Professor of electrical engineering. His main research area is in application of computer technology to power system monitoring, operation, protection and control. His other research interests include GPS time transfer and chaotic dynamics and their application to system problems. Dr. Liu serves as a Reviewer for IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS, IEEE TRANSACTIONS ON POWER SYSTEMS, and IEEE TRANSACTIONS ON POWER DELIVERY. Chi-Shan Yu was born in Taipei, Taiwan, R.O.C., in He received the B.S. and M.S. degrees in electrical engineering from National Tsing Hua University, Beijing, China, in 1988 and 1990, respectively. He is currently pursuing the Ph.D. degree in electrical engineering at National Taiwan University, Taipei, Taiwan. Since 1991, he has been with Private Kuang-Wu Institute of Technology and Commerce, Taipei, he is an Instructor of electrical engineering. His current research interests are computer relaying and transient stability control.