New Line Current Differential Relay using GPS ...

Paper accepted for presentation at 2003 IEEE Bologna Power Tech Conference, June 23th-26th, Bologna, Italy

New Line Current Differential Relay using GPS Synchronization Ian Hall, Phil G. Beaumont, Gareth P. Baber, Itsuo Shuto, Masamichi Saga, Koichi Okuno, and Hachidai Ito

Abstract-- The "numerical line current differential relay" has proved to be one of the most successful types of transmission line protection system, and advances in communication technology have facilitated its ever wider application. However, more recently, the adoption of SDH (Synchronous Digital Hierarchy) as the international standard for high speed data communication over optical fiber and microwave has given rise to communications links with characteristics which are unsuitable for traditional numerical line current differential relays. Therefore, we have developed a new "line current differential relay" using GPS (Global Positioning System) synchronization that is applicable for use over SDH communication networks. Following successful completion of type testing and twelve month field trials with NG, (National Grid) in the United Kingdom, type registration was achieved in April 2001. Subsequently, the first commercial units were delivered in September 2001 and commissioned in June 2002. Index Terms--Power system protection, Protective relaying, Global Positioning System, Synchronization, Synchronous digital hierarchy, Pulse code modulation

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I. INTRODUCTION

M T&D Corporation’s “line current differential relay” samples the power system current at a sampling frequency of 600Hz, quantizing the sampled data to 12 bit resolution. The instantaneous sampled data for each of the three phases is transmitted at a rate of 64kbit/s. In the conventional relay, a method of synchronization has been applied to ensure that samples are taken simultaneously by relays in substations at opposite ends of the power transmission line/cable, on the premise that the propagation delays in the communication link are equal for the send and receive paths. However, the recently adopted technology of SDH communications for high speed data communication can exhibit different propagation delays between the send and receive paths, with the result that the conventional method of achieving synchronized sampling cannot be applied. Therefore, we have developed a new "line current differential relay" that can achieve synchronization based on GPS (Global Positioning System) time information, independently of the Ian Hall is with National Grid Transco plc, Wokingham, UK. Phil G. Beaumont and Gareth P. Baber are with TM T&D Corporation, Durham, UK. Itsuo Shuto, Masamichi Saga, Koichi Okuno and Hachidai Ito are with TM T&D Corporation, Tokyo, Japan.

0-7803-7967-5/03/$17.00 ©2003 IEEE

characteristics of the communication medium. Each relay receives synchronizing information from the satellite based timing system via GPS receivers installed in the substations, and samples the power system current according to this time information. Furthermore, we have applied a unique back-up mode function which can maintain the performance of the protection in the unlikely event of failure of the GPS reception system. II. SDH COMMUNICATION NETWORKS AND THEIR IMPACT ON LINE CURRENT DIFFERENTIAL RELAYS The rapid growth of digital networks and the convergence of telephone and high-speed data networks have enforced the development of new standards. Proposals in ITU-T, (formerly CCITT) for a Broadband Integrated Services Digital Network (B-ISDN) were an enabler for a new synchronous multiplexing standard that would better support switched broadband services. The new standard first appeared as SONET (Synchronous Optical Network) in the United States. Initially, the objective of the SONET standard was to establish a North American standard that would permit interworking of equipment from multiple vendors. Also at that time, a different standard for digital hierarchies was in use in Japan. Subsequently, the ITU-T was approached with the objective of developing a world-wide standard. Despite the historical differences between the North American, European and Japanese digital hierarchies, this goal was achieved with the adoption of the SDH standards (1988). Fig. 1 shows these different standards in Europe, North America & Japan and Ame rica

Japan

Euro pe

SDH (world s tandard) N * 155.5M bps

397.2Mbps 97.73Mbps

274.2Mbps

139.3Mbps

155.5M bps

32.06Mbps

44.73Mbps

34.37Mbps

51.84M bps

6.31Mbps

8.448Mbps

6M bps

1.544Mbps

2.048Mbps

Conventional propagation method (PDH)

1.544Mbps

i) Simplification of multiplexer ii) Shortening of propagation delay time iii) World-standard transmission speed

Fig. 1 Conventional propagation method and SDH in respective countries

P ropa g a tion route a t the tim e of defective m ain rou te

Propagation route at the time of defective main route Standby From Ass to Bss (Back up path)

Sta n db y (B ack u p pa th )

Propagation delay time: Yms

U su al prop ag a tion ro ute M a in SD H SD H (W ork er Path)

M U X N o de MUX

P C M rela y

Usual propagation route

M U X N ode

2M bps

2M bps MUX

S ub station A

MUX

P C M relay S ub sta tion B

Fig. 2 SDH network (‘normal’)

Fro m A ss to B ss

U sual propagation route SD H M U X N ode

From Bss to Ass Propagation delay time: Xms MUX MUX

PCM relay Substation A

P ropagation rou te at the tim e of defective m ain route Stand by (B ack u p p ath)

SDH MUX Node

SDH MUX Node

SD H M U X N ode

MUX

PCM relay Substation B

Fig. 4 SDH network (Occurrence of different propagation delay time between send and receive paths – ‘split path’) O ccurrence of different propagation delay tim e betw een send and receive paths in the com m unication netw ork

C on ventional current differential relay – sam pling synchronization error

Fro m B ss to A ss M UX

M UX

Standb y

M UX

(B ack up path)

P C M relay S ub station A

P CM relay

Sub station B

Fig. 3 SDH network (with defective propagation route)

SDH hierarchies. In synchronous networks, all multiplexing functions operate synchronously using clocks derived from a common source. SDH/SONET are expected to dominate transmission for decades to come, as the multiplexing structure has been designed to carry not only current services but also emerging ones using ATM and/or IP framing structures for example. SDH allows the development of network topologies that are able to achieve ‘network protection’, that is, they are able to survive failures in the network by reconfiguring and maintaining services by alternate means. One of the methods that can be employed to provide network protection is by the use of self-healing ring architectures. Protection switching in a ring topology can be either ‘uni-directional’ or ‘bidirectional’. Uni-directional means that only the faulted path is switched whilst the non-faulted path follows the original route. With bi-directional protection both the go and return path are switched to follow the opposite direction along the ring. The important point to note is that bi-directional switching will maintain equal signal propagation delays for the go and return path (any differences will be transient), whilst unidirectional switching may introduce permanent, unequal propagation delays that can cause severe difficulties for current differential relays. The creation of unequal delays is illustrated in Fig. 2, Fig. 3, and Fig. 4. Comparison of measured quantities from differential protection relays must be based on pairs of samples that were taken at the same sampling instant. As samples are transferred to the remote end of the protected circuit for comparison, the delay that is introduced by the telecommunications link has to be compensated by the protection relay that performs the

F rom A SS to B SS P ropaga tion delay tim e: Y m s

SDH M U X N ode

SD H M U X N od e

From B SS to A SS Propaga tion delay time: X m s M UX

P C M relay

M UX

S ubstation A

M UX

P C M relay

Sub station B 5

Fig. 5 Influence on Line Current Differential Relay comparison. However, if the sampling clocks are synchronised at each terminal (see later), the process is simplified to one of comparing referenced current samples which are derived from synchronous clocks. With the introduction of SDH communication systems it is essential that the comparison of the respective samples does not depend on equal signal propagation delay times for the send and receive paths nor on stringent limitations for signal propagation time variations. Fig. 5 shows that the occurrence of a different propagation delay time between the send and receive paths in the communication network will result in a sampling synchronization error for a conventional current differential relay. III. NEW LINE CURRENT DIFFERENTIAL RELAY USING GPS SYNCHRONISATION FOR NG IN THE UK A. Line Current Differential Relay Scheme using Instantaneous Current Values 1)Segregated-phase current differential protection using instantaneous current data: Current differential protection is an ideal protection for transmission lines and has the following features:- High selectivity for all types of fault even on complex power systems with multi-terminal transmission lines and series compensation

- High speed operation with high sensitivity even for transmission lines with weak infeed or no-infeed terminals - Stable operation in the presence of high frequency ac components and dc components generated during power system faults - Not reliant on complex starting arrangements to obviate the effect of capacitance current at low loads, for example, as in phase comparison systems. TM T&D’s current differential relay provides segregatedphase current differential protection for both phase to phase and phase to ground faults. The segregated-phase current differential protection ensures high selectivity and sensitivity for various types of fault. Figure 6 shows its dual slope bias characteristic. Terminal X

IY

IX

GRL100

IZ

Relay-B

GRL100

Terminal Z

ib5

ib4

ib1

ib7

ib6

ib1

ib2

ib3

ib1

ib2

ib4

ib5

ib6

ib7

ib4

ib5

ib6

Data transmission frames

transmission delay time

Relay-A

ib1

ib2

ib3

id1

id2

id3

ia3

ia2

ib3

ib7

ia5

ia4

ia1

ia7

ia6

Fig. 7 Concept of current differential calculation

Terminal Y

GRL100

ib3

ib2

the current differential calculation can be correctly performed using synchronized samples having the same sampling reference number. The current differential relay has a typical operating time of 16ms following the occurrence of a fault. 2) Sampling timing synchronization with communication system: t1

t1

Ry-B Operating zone Id Iset

Large current region characteristic (Slope = 1)

Small current region characteristic (Slope = 1/6)

Id: Differential current (|IX + IY + IZ|) ΣI: Restraining current (|IX| + |IY| + |IZ|)

Ry-A

t2 (a) No sampling timing error t1 = t2 = td

∆t

∆t

td

td

t2

(b) Sampling timing error = ∆t t1 = td + ∆t t2 = td - ∆t 2∆t = t1 - t2

Fig. 8 Sampling timing synchronisation

Fig. 6 Percentage ratio differential characteristics Sampled instantaneous current values are sent from one terminal to the other every 30 electrical degrees, as illustrated for the case of a two-terminal power transmission line in Fig. 7. Relays ‘A’ and ‘B’ installed at respective ends of the protected circuit, sample the power system current data simultaneously using the sampling synchronization method described later in clause (2). Relay-B transmits the current data sample (ib) complete with reference number to relay-A. Relay-A then performs a current differential calculation using the referenced current data sample (ia) from its own terminal and (ib) from the remote terminal, where the samples (ia) and (ib) have the same sample reference number. Even if the reception of the transmitted data frame from the remote terminal is delayed to the extent of the propagation delay time,

In order to carry out the current differential calculation described previously, it is necessary to perform synchronized sampling at all terminals. In order to achieve this, Toshiba’s conventional current differential relay performs sampling timing synchronization by assuming that the propagation delay time, (td) of the send and receive communication paths between the two terminals are equal. Fig. 8 shows the method used to achieve sampling timing synchronization. In case (a) No sampling timing error, t1=t2=td; and in case (b) Sampling timing error of ∆t, t1-t2=2∆t. The values of t1 and t2 are used to calculate the sampling timing error and hence sampling timing control.

3) Sampling synchronization with SDH communication: In the case of an SDH communication network, where the propagation delays of the send and receive transmission paths (tdu and tdd) may be different, the conventional method of sampling timing synchronization cannot be employed, for the reasons illustrated in figure 9-(b). This is because the conventional method will adjust the clock relationships to cause t1 and t2 (as seen by the relay) to be equal, when in reality they are not. A sampling timing error of t = (tdu tdd)/2 is thereby generated. Consequently, an erroneous differential current, Id is measured by the relay which will cause the relay to operate incorrectly if the Id setting value is exceeded.

t1 Relay-B

tdd

tdu

Relay-A

t2 (a) tdu=tdd :No sampling timing error t1

Relay-B

∆t tdd

tdu

sampling of the current data and a resultant increase in the calculated differential current (Id). Therefore, it is not advisable to apply a conventional current differential relay using an SDH communication network. However, the method of conventional sampling synchronisation employed by the relay (see earlier) provides a high degree of tolerance to the transient unequal delay which arises from bi-directional switching. This is because the relay takes a finite time to adjust the clock relationships and it takes longer to generate a significant error than the transient period of the unequal delay. This may be an important consideration in using the conventional relay as the final part of a fallback strategy in the unlikely event where GPS signals are not available. B. GPS Synchronization Scheme 1)SDH communication system: In an SDH communication network, the propagation delays in the send and receive paths between the relays may change dynamically as a result of automatic, uni-directional switching of the communication route. The conventional synchronization system for current differential relays requires that the propagation delay times be equal and therefore, cannot be utilized. Sampling synchronization is accomplished in the new relay by using GPS time information, and as such, synchronization is independent of the characteristics of the communication medium. Furthermore, the relay provides a unique GPS synchronization back-up mode function, which can maintain the performance of the protection despite changes in the propagation delay time, even in the unlikely event of failure of the GPS reception system. 2)GPS Synchronization system:

Relay-A

t2

(b) tdu ≠ tdd Sampling timing error: ∆t=(tdu-tdd )/2 in spite of t1- t2 = 0 Fig. 9 Sampling timing synchronization with different propagation delays between send and receive paths The SDH communication network established in the UK uses a ring topology within which the communication route is automatically switched from the main (worker) path to the back-up (protection) path in the event of a failure occurring in the main path. The switching protocol depends on the communication provider, and may be uni-directional. In fact, uni-directional switching is normally preferred, because only one communication disturbance arises as a result of path switching. In the case of uni-directional switching, a difference in the propagation delay between the transmit and receive paths is generated in the event of a defect in one of the paths. As stated previously, the difference in propagation delay times may result in mal-operation of a conventional current differential relay, since it causes a timing error in the

S/S A

S/S B

GRL100

GPS receiver Sampling OSC

GRL100

communication system

Sampling OSC

GPS receiver

Fig. 10 Configuration of GPS synchronous Current Differential relay Each relay measures the time difference between the output of its own sampling oscillator and the one pulse per second (1pps) GPS signal. Each relay then corrects the oscillation frequency of its sampling oscillator so that the time difference becomes zero. The relay continuously updates the correction factor and stores it as the absolute accuracy of the oscillator. In the event of the GPS signal being lost, the relay is able to control the oscillator’s free-running frequency error to within

0.2ppm, by using the correction factor stored immediately prior to the loss of the GPS signal. By this method, the sampling synchronization error between two relays can be limited to within 1.5µs. Fig.11 shows the GPS standard time signal that is provided to the relay from the GPS receiver. The standard time data is encoded so that any failure or corruption of the standard time signal can be detected by the relays, thus ensuring that sampling synchronization control is not adversely affected.

t2 Ry A

Ry B

t1

Standard 1pps signal

Fig. 12(b) Synchronization control using recorded transmission delay time

Time data

1 second

Fig. 11 GPS standard time signal 3) GPS backup system: Since the alignment of GPS satellites changes during the course of a day, the GPS antenna must be installed carefully with an unobstructed view of the sky, otherwise reception of the GPS time signal may be interrupted. In order to alleviate this problem and other potential causes of interruption of the GPS time signal, a back-up function has been developed that allows sampling synchronization control to continue during an interruption to the GPS time synchronization signal. Further, the back-up function can maintain sampling synchronization even in the event of the SDH communication path being switched during the period of interruption to the GPS time synchronization signal. Fig.12 (a) (b) (c) shows the sampling synchronization control system during periods of normal mode operation and backup mode operation. a)MODE 0: operation under normal conditions: Fig.12(a) shows the operating state during normal reception of the GPS standard time signal. In this state, relays A and B continuously record timing information t1 and t2 for

the signal received from the other terminal. Because the sampling time of relays A and B are synchronized by GPS, t1 and t2 are equal to the propagation delay time between relays A and B respectively. Changes in communication path propagation delay time caused by switching of the SDH network have no effect on the sampling timing of the relays. b)MODE 1: operation following loss of the GPS signal: Fig.12(b) shows sampling synchronization control following loss of the GPS signal at terminal B. The relay at the terminal which has lost its GPS standard time signal becomes the ‘slave’ and controls the frequency of its internal oscillator so that the signal timing information for the signal received from the other end is maintained at a value of t1, where t1 is the propagation delay recorded immediately prior to loss of the GPS signal. In the event that the GPS time signal is lost at both terminals then the relay which lost its signal first becomes the slave, and synchronization is maintained at both ends by carrying out sampling synchronization control in the back-up mode. Fig.12(c) shows sampling synchronization control in the event of the SDH communication path being switched during the period of interruption to the GPS time synchronization signal. Relay B will detect the sudden change in the timing of

t2 Ry A

t2

Change of transmission delay time

Ry A

Ry B

t1 t1’

Ry B

t1

Fig. 12(a) Synchronization control by GPS signal (normal state)

Fig. 12(c) Change of transmission delay time during Synchronization control by recorded transmission delay time

the received signal since switching of a path in the SDH network takes a period of several milliseconds. Having detected a sudden change of propagation delay time, the relay records the new value of delay time t1’, and continues to carry out sampling synchronization control according to the new delay time. GPS lost MODE 0 GPS GPS ON GPS ON synchronisation

MODE 2 Conventional synchronisation

GPS ON

87 Element LOCK

Manual or automatic

MODE 1 Recorded data synchronisation Phase difference >Pcur

Phase difference > Pcur

Fig. 13 Mode transition diagram If relay B is unable to receive the signal sent from relay A due to a failure in the communication link, then it cannot continue to perform sampling synchronization control. Under these conditions the sampling oscillator is allowed to run free. After subsequent recovery of the communication link, the actual transmission time of signals received from relay A differs from the recorded time by an error which is proportional to the length of time for which the oscillator was in a free-running condition. Therefore, Mode 1 operation incorporates a limitation of allowable free-running time, after which the differential protection element is locked, since sampling synchronization can no longer be guaranteed. c) MODE 2: operation without GPS time signal and following a prolonged period of communication failure: If, during MODE 1 operation, the allowable free-running time is exceeded, or if the dc power supply to the relays is removed causing loss of recorded propagation delay data, then back-up operation changes from MODE 1 to MODE 2. MODE 2 operation provides sampling synchronization control based on the assumption that the propagation delay times of the send and receive paths are approximately equal. This mode is used after having checked the difference in propagation delay times of the SDH communication link. However, the transition from MODE 1 to MODE 2 may be made automatically by using a check of the phase difference of the current between the terminals at each line end (see below). d)Current phase difference monitoring system: In order to continuously monitor the performance of the sampling synchronization control system, the relay is provided with a function for checking the phase difference between the currents at the relay terminals. The function operates when the measured current phase difference exceeds a specified threshold. The threshold can be adjusted since the measured

current phase difference may be greatly influenced by the line charging current, particularly in cases of low load current. Fig. 13 shows the transition diagram for the sampling synchronization control modes described previously. C. Site Trial As part of the type registration process for the line current differential relay operating over an SDH communication network, the following site trial was carried out with NG in the UK. - Trial operation: Duration 12 months commencing 12 October 2000 - Location: Bramley and West Weybridge 400kV substations (line length approx. 50km) The site trial was performed with the relays connected in the main protection current transformer secondary circuit and communication was via an SDH network. Fig. 14 shows the trial relay set installed at West Weybridge substation. A modem was connected to each line current differential relay so that recorded data could be accessed remotely. No system malfunctions were experienced during the trial period. Furthermore, sampling synchronization was successfully maintained when the GPS standard time signal was deliberately interrupted. - Sampling synchronization tests: Duration 2 days commencing 30 January 2001 - Location: Bramley and West Weybridge substations Extensive testing of the relay sampling synchronization control system was carried out with the assistance of NG engineering staff. The purpose of these tests was to confirm that sampling synchronization was maintained despite interruption of the GPS standard time signal, and also to confirm the stability of the system in the event of the communication path being switched or becoming defective. The tests were undertaken for all modes of operation and were completed successfully with type registration being achieved for two-terminal operation on April 23, 2001, and for threeterminal operation on March 6, 2002.

- It was confirmed that the current differential protection was blocked in the event of the communication channel becoming defective. - It was confirmed that sampling synchronization was maintained even in the event of switching of the SDH communication path. - It was confirmed that the sampling synchronization error did not increase in the event of the GPS standard time signal being interrupted, even with repeated switching of the SDH communication path during the period of GPS interruption. - It was confirmed that, during GPS back-up mode operation, the differential protection was locked (MODE

2A) in the event that sampling synchronization could not be maintained due to the communication path being defective for a prolonged period. - It was confirmed that the current differential protection relay system performed correctly for uni-directional and bi-directional switching tests, automatic reversion and ‘split path’ conditions on the SDH communication network. - It was confirmed that the relay could also operate

correctly when using conventional synchronisation during network bi-directional switching operations. D. Practical Relay System for NG The Configuration of GPS-based Current Differential Protection System is shown in Fig. 15. The GRL100 line current differential relay is connected to the GPS receiver using optical fiber cable. The GPS receiver provides eight optical output ports, and can supply the GPS standard time signal to a maximum of eight relays. The GRL100 relay is also connected to the Cross-Site Fiber Link (CSFL) unit using optical fiber cables. Optical fibers of graded-index multi-mode 50/125µm type are used. The Cross-Site Fiber Link (CSFL) unit converts the optical signals to CCITT X.21 electrical signals for connection to the primary multiplexer at 64Kbits/s. The primary multiplexer connects to the SDH network. IV. CONCLUSION This paper described a newly developed “line current differential relay” which achieves synchronization of sampling timing between two or more substations using GPS standard time information, and has a powerful back up system allowing performance to be maintained even in the unlikely

Fig. 14 Trial System of GPS-based Current Differential Protection

Optical fibre Antenna cable

Antenna cable

Terminal A GRL100 - 21 2W

GPS

Terminal B GPS Receiver

GPS Receiver

GRL100 - 212W

GPS

SDH communication system TX1 C S F L

RX1 CK1

Optical fibres

M

M

U

U

X

X

MUX: Multiplexer

(SDH terminal)

C S F L

Metallic cables

CSFL : Cross - Site Fibre Link unit

Fig. 15 Configuration of GPS-based Current Differential Protection System

TX1 RX1 CK1

event of the GPS signal being interrupted. The back up system is capable of maintaining synchronism for multiple SDH path switching events during the period of GPS interruption. Furthermore, a current phase detector allows automatic safe transition to conventional synchronisation when no current phase errors are detected. Conventional synchronisation also performs correctly during SDH network bi-directional switching. As a result of this development, the “line current differential relay” can be applied to transmission line protection with communication over increasingly prevalent SDH networks, which exhibit different propagation delays between the send and receive paths as well as automatic switching of the communication route during operation. The newly developed “line current differential relay” was installed in the North Hyde and Iver substations of National Grid Company plc in the UK, and was successfully commissioned in June 2002. More relays are expected to be installed in other substations in the future.

Itsuo Shuto received his BS and ME degrees in engineering from Tokyo Institute of Technology, Tokyo Japan. He joined Toshiba, now TM T&D Corporation, in 1978, and is currently responsible for development of protection and control systems.

Masamichi Saga graduated from The University of Electro-Communications, Tokyo. He joined Toshiba, now TM T&D corporation, in 1991. His special fields of interest included software development of numerical protection relays.

V. REFERENCES [1]

[2] [3] [4]

[5]

M. Yamaura, J. Inagaki, K. Igarashi, I. Shuto, K. Hashisako, C Shitomi, N. Inoue: “Development of digital current differential relay built-in sampling synchronization function” at K(Korea)IEE annual conference. Power systems and apparatus, 1988-11 M. Yamaura, Y. Kurosawa, H. Ayakawa: “Improvement of internal charging current compensation for transmission line differential protection” at 6th IEE international conference, 1997-3 K. Igarashi, Y. Sukegawa, I. Shuto, H. Amoh and M. Saga: "Development of high-speed numerical line differential relay" at International Conference on Electrical Engineering '99, 1999-8 Y. Serizawa, S. Miyazaki, K. Shimizu, S. Suzuki, M. Hori, J. Takeuchi, M. Inukai, “Wide-Band Digital Communication Requirements for Differential Teleprotection Signalling” at CIGRE Symposium, Helsinki, 1995. CIGRE Joint WG. 34/35.11 Protection using Telecommunications, August 2001

VI. BIOGRAPHIES Ian Hall graduated from Imperial College, and is a member of the IEE. He has held senior system engineering posts in the computer industry and joined NG in 1988. At NG he has been a senior technical specialist with responsibility for the specification and performance of protection control and communication systems and is currently responsible for the management of NG's communication providers.

Phil G. Beaumont is chief engineer for protection and control at TM T&D Corporation, Protection Systems Division. He is principally responsible for product development and technical marketing of protection and control systems. Phil Beaumont is a member of the IEEE and IEE.

Koichi Okuno graduated from Yokohama National University. His employment experience has been with TM T&D Corporation since 1994 working in R&D and applications. He is now based in TM T&D's protection and control office in the UK.

Gareth P. Baber graduated from the University of Salford in 1991. He is Product Development Manager at TM T&D Corporation, Protection Systems Division, and is responsible for development of protection and control systems. He is a member of the IEE.

Hachidai Ito received his BS and ME degrees in electrical engineering from Kyoto University, Kyoto, Japan and his MS degree in Computer Science from University of Maryland, College Park, Maryland. He joined Toshiba Corporation in 1981 and is currently manager of the Protection and Control Development Department of the Protection Systems Division at TM T&D Corporation. He is principally responsible for product development of protection equipment and control systems. He is a member of IEEE, IEEJ and IEICE.