Abstract--This paper describes the field experience and

assessment of a GPS signal receiving and distribution system for synchronizing power system protection, control and monitoring. Application of GPS synchronization to protection, control and monitoring systems is becoming more popular in the field of power systems. However, the actual performance and reliability of GPS signal receipt within the substation environment has not been comprehensively assessed. This paper includes the system configuration for GPS synchronization, the results of our assessment of GPS synchronizing signal receipt in terms of performance and reliability. The authors introduce several techniques for reliably applying GPS synchronization to power system protection, control and monitoring especially in the event of GPS signal loss or failure. A T-RAIM, (Time Receiver autonomous integrity monitoring) function has been tested and the ability to maintain synchronizing signal stability was observed when a satellite anomaly occurred in January 2004. The actual service experience of a GPS based line current differential relay developed by the authors and now in commercial operation in Europe are described in this paper.

Index Terms--Control, Current differential relay, Fault locator, GPS, Monitoring, Phasor measurement, Protection, Satellite Anomaly, Signal Encoding, Time Synchronization, T-RAIM.

I. NOMENCLATURE GPS Global Positioning System IRIG Inter-Range Instrumentation Group PMU Phasor measurement unit PPS Pulse per second T-RAIM Time receiver autonomous integrity monitoring

II. INTRODUCTION HE authors have developed a GPS time synchronizing signal distribution technique for protection and control

systems [1]-[3]. Actual systems have been realized including a

D. Itagaki, K. Ohashi, I. Shuto and H.Ito are with Toshiba Corporation,

Tokyo, Japan. 0-7803-9525-5/06/$20.00 ©2006 IEEE.

fault locator, power system status estimator or analyzer(PMU etc.), and line differential relay using GPS synchronization. These systems are operating in Japan and Europe, and successful results have been achieved [4][5].

Although receipt of the GPS satellite signal has to be stable in these systems, sufficient data such as long-term stability monitoring of GPS signal receiving performance in substations is not open to the public.

The authors have developed a GPS time synchronizing signal distribution technique that has the high reliability and resolution required for protection and control systems, and have applied this technique in several applications. In this process, we have monitored the status of the GPS signal received in a number of substations.

In this paper, both the system configuration of the GPS synchronization system and an assessment of the data obtained from the investigation into the performance of GPS synchronizing signal receipt have been considered and the results reported. Furthermore, several techniques are reported for reliably applying a GPS synchronization signal to power system protection and control. The T-RAIM function has been tested as a countermeasure to GPS satellite anomalies. When the satellite anomaly occurred in January 2004, the consequence was that an incorrect positioning result was calculated and a loss of synchronizing signal output in GPS receivers. We had actually been monitoring the synchronizing signal in our factory during this period and observed that the synchronizing signal could be continuously output if the T-RAIM function was used. These techniques are applied to our GPS based line current differential relay.

III. SYSTEM CONFIGURATION OF GPS SYNCHRONIZATION IN SUBSTATION

A. Present distribution technique Fig. 1 shows an outline of the requirements for resolution

and reliability of a GPS synchronization signal in various applications for power system protection and control. At present, the IRIG-B timing code is widely used for time synchronization for substation equipment [6]. This code is amplitude modulated on a 1kHz carrier and distributed by copper based coaxial cable. Although IRIG-B can be used in

Field Experience and Assessment of GPS Signal Receiving and Distribution System for

Synchronizing Power System Protection, Control and Monitoring

Daiju Itagaki, Kenichiro Ohashi, Itsuo Shuto, and Hachidai Ito, Member, IEEE

T

event recording with a time resolution of one millisecond, it is difficult to achieve synchronization with the high precision required in some practical cases such as protection, fault location and phasor measurement.

Fig. 1. Requirement for GPS synchronization.

In order to solve these problems, the application of a digital

signal is necessary. A 1PPS (one pulse per second with edge co-incident with the second change) signal distributed by optical fiber is often used for synchronization in phasor measurement systems [7].

Using 1PPS, 1 microsecond order of precision is available and is adequate for fault location or protection relay applications. However, possible signal noise or optical device deterioration may cause waveform degradation resulting in incorrect timing edge detection. Particularly, protection relays require high reliability synchronization because incorrect timing synchronization may cause relay mal-operation.

Fig. 2 shows the mechanism of the problem. In general, synchronization is performed on time with an optical signal edge (optical signal turn on or off) indicating 1PPS timing. This timing edge is detected when the electrical voltage output from the O/E converting device changes at the threshold level.

If the optical device deteriorates and the voltage output changes at the threshold level, incorrect timing edge detection and erroneous detection of the 1PPS timing signal may occur.

Should either of these events take place in a current differential relay installed at one end of a transmission line, the calculated current values using the sampling result of

instantaneous data will be different from that calculated in the current differential relay installed at the other end of the protected line and the current differential function may operate incorrectly.

incorrect detection

(a) 1PPS signal before transfer

(b) Received signal

Time

Threshold level

(a)

(c) Detected timing

(b) (c)

Optical device deterioration

GPS Receiver

E/O Conv.

O/E Conv.

Edge detect

correct detection

Optical fiber

1PPS

Fig. 2. Incorrect 1PPS edge detection caused by device deterioration.

B. Proposed distribution technique Fig. 3 shows the new synchronizing signal distribution

system. A commercial GPS receiver and digital signal processing technique are used. The GPS receiver receives a signal from GPS satellites via the antenna. A high precision 1PPS signal is output together with serial data containing date and time information. These electrical signals are converted to optical signals and distributed via an optical fiber. Therefore, high precision timing synchronization can be achieved.

The 1PPS signal is encoded to a base timing code and distributed by optical fiber. Firstly, the relays synchronize data sampling timing only when timing code is received. Therefore, incorrect timing edge detection caused by signal noise or optical device deterioration is avoided. Secondly, serial data containing date and time information from the receiver is superimposed with the timing code. Hence, only a single optical fiber is needed to distribute the data. Serial data in asynchronous communication (start / stop transmission) format is suitable for microprocessor based equipment in substations and there is no need for special decoding circuitry.

Fig. 3. System configuration of the new time synchronizing signal distribution.

Commercial GPS Receiver

E O conversion Superimposing

Single Optical Fiber 1 PPS signal

Serial Data

GPS Antenna Encoding

Protective Relay Fault Locator Phasor Measurement

Timing Code Serial Data

(Date, Time)

(Date, Time) (1 PPS signal)

C. High reliability method of synchronization by optical signal encoding

A digital signal such as a 1PPS signal is needed to achieve synchronization with the required high resolution. However, for the reasons described previously, it is difficult to achieve synchronization with the high reliability required under conditions when signal noise is present or deterioration in optical devices is experienced.

The best solution for this problem is encoding the 1PPS signal before its transmission. The 1PPS signal is encoded to a base timing code. The relays synchronize data sampling timing at the point at which the code is received only when the pattern conformity is confirmed between original/known signal pattern and the transmitted signal pattern. By using this technique, even if voltage output oscillation is caused by optical device deterioration, original code is not detected and erroneous detection of the 1PPS timing does not occur. Loss of timing code detection of the original 1PPS timing caused by signal deterioration is not a problem because synchronization can be maintained by the provision of a self-running function.

Furthermore, to avoid erroneous detection caused by noise having a frequency that coincides with the code, the code pattern (raw data 1 and data 0) should be selected carefully to be as random as possible.

In the receiving process, if the input signal is sampled discretely and the sampling rate is comparable to the bit rate of the code, it is possible that the sampling result of the oscillating signal coincides with the original code pattern accidentally as a consequence of optical device deterioration as shown in Fig. 4.

Received signal

Sampled result

Accidentally coincide with original code

Waveform before Transfer

Threshold level

Detected timing

1PPS

Fig. 4. Erroneous detection of code due to device deterioration.

As described previously, because the optical signal

contains not only the timing code but also serial data, this erroneous detection occurs at a different time to the original 1PPS timing. This erroneous detection can be avoided if the sampling and collation rate is higher than the code bit rate.

D. System simplification using modern communication techniques

IRIG-B requires unique hardware and software to decode the timing signal.

On the other hand, GPS receivers designed for time transfer based on a GPS receiver commonly used for

navigation purposes outputs time data in asynchronous communication (start/stop transmission) that is suitable for microprocessor based equipment. Serial data that contains information such as date or time is transmitted generally in 4800 bps according to NMEA-0183 protocol defined by National Marine Electronic Association (NMEA).

NMEA-0183 messages generally take the following form. The first address field indicates the type of message. The next field indicates the data such as date, time, position, or positioning status required for the monitoring of GPS signal receive status.

$<address field>,<data field>……[<check sum field>]<CR><LF>

“0” “1” “1”“1” (Ref)

(a)IRIG-B Signal

Stop Bit

Start Bit (b)Asynchronous Communication

(Ref)

Fig. 5. Time data format.

E. Reduction of optical fiber by superimposing signals In practice it is frequently found that individual cables have

been used to transmit the IRIG-B code and the 1PPS signal which adds to the overall cost. A desirable cost reduction can be achieved if signals are superimposed and transmitted using a single cable.

Fig. 6 shows the configuration of the hardware and signal processing. Signal encoding and superimposing is processed by a programmable logic device (PLD) or a field programmable gate array (FPGA). The 1PPS signal that is output from the receiver is encoded and superimposed with the serial data and transmitted via optical fiber.

GPS receiver

(a)1PPS signal

(b)Serial Data

Antenna Encoding

(c)

E/O conversion Superimposing LSI (PLD or FPGA)

(a)

(b)

Encoded 1PPS Serial Data

(c)

Fig. 6. Signal processing. Fig. 7 shows the GPS based time synchronizing signal distribution unit.

(c)1PPS signal encoding device in the unit

(a)Multi port type

(b)Single port type

Fig. 7. GPS based time synchronizing signal distribution unit (Type HHGP1 and Type HNGP2).

Fig. 8 shows the configuration of a synchronizing signal distribution system in a substation. For example, the GPS antenna is installed on the roof of the relay room and connected to a GPS based time synchronizing signal distribution unit using coaxial cable. The time synchronizing signal is distributed from the GPS based time synchronizing signal distribution unit to protection and control equipment using optical fiber. Because the GPS based time synchronizing signal distribution unit has many optical output ports and cascade connection is possible, it is easy to distribute the synchronizing signal to many protection and control devices.

For protection relay applications, we developed a new line current differential relay using GPS synchronization that is applicable for use with SDH communication networks*. This type of relay has been in use since 2001 and commercial operation commenced in the United Kingdom in 2002.

*http://www.toshiba.co.jp/f-ene/tands/english/protect/f_gr_s_r.htm GPS antenna

(on the roof)

Surge Arrester

GPS based time synchronizing signal

distribution unit

Cascading connection unit

Protection and control equipment Coaxial cable

Optical fiber

Fig.8. Configuration of synchronizing signal distribution system.

IV. THE ASSESSMENT RESULT OF GPS SATELITE SIGNAL RECEIVING STABILITY

In this section the results of our assessment of the stability of GPS satellite signal receipt under various conditions are reported.

A. Regarding GPS The GPS system consists of 24 satellites in orbit around the

earth, positioning is available 24 hours a day all around the world. The launch of GPS satellites has continued and the number of usable satellites reached 27 in 1996, and generally 28 or 29 in recent years. Therefore, a sufficient number of satellites are available even if some satellites are not always usable.

The satellites are arranged in six orbital planes that have an inclination angle of 55 degrees relative to the earth’s equator. The satellites complete one orbit in about 11 hours and 58 minutes, and trace a track approximately once a day (23 hour 56 minutes) on the earth.

Although satellite constellation changes through a day, more than 8 satellites are usable above the horizontal if 24 satellites are in operation. Although conditions change according to the position of the earth, a sufficient number of satellites can be used. Furthermore, the satellite signal is not apt to degrade in poor weather conditions.

B. Assessment result of long-term receiving stability of GPS signal in substation

The GPS based time synchronizing signal distribution unit can maintain a 1PPS signal output if at least one satellite can be received. If an antenna is installed in a location that offers an unobstructed view of the sky, at least 4 satellite signals can be received and therefore there seems to be little possibility to experience a loss of the 1PPS signal. However, because there are high voltage lines and equipment in a substation the possibility that they might affect GPS signal receipt must be considered. The authors have undertaken long-term monitoring of GPS signal receipt. Fig. 9 shows the configuration of the monitoring system. The 1PPS output from the GPS receiver is monitored every second 24 hours a day. Even if only one of the 1PPS signals is lost it can be detected and recorded. If receipt of the GPS signal is not possible, loss of the 1PPS signal output occurs instantaneously and the event is recorded. The healthy of the monitoring system is checked daily and recorded at a predetermined time.

Synchronization signal

GPS unit Network

Computing Terminal

GPS antenna

Optical fiber

Coaxial cable

Personal Computer

Fig. 9. Configuration of 1PPS signal monitoring system.

Table 1 shows the results obtained. The monitoring periods

cover all seasons of the year by combining the results obtained, therefore the seasonal effects of the weather can be observed.

Substation B is a 275kV substation and various transmission equipments exist, therefore the effect of surge from the equipments can be observed. In substation B and C, no loss of 1PPS signal has been observed, therefore a stable receiving result is reported. In substation A and Toshiba’s Fuchu Complex, 10ppm order of interruption has been observed, but this order of interruption can be tolerated in the application system described later. The cause of GPS signal loss estimated is listed below.

Obstruction around GPS antenna Signal attenuation due to interference by reflected signals Signal attenuation in the coaxial cable from the antenna

GPS antenna Fig. 10. GPS antenna installation in substation A.

Fig. 10 shows the antenna installation arrangement in

substation A. There is a parabola antenna near the GPS antenna and it was thought that the parabola antenna affect as obstruction and the number of usable satellites decreased.

Fig. 11 shows the antenna at Toshiba’s Fuchu Complex. The graph on the right-hand side shows the paths traced by GPS satellites. The thick dots show that the satellite signal to noise ratio was degraded below permissible levels and the satellites from this direction were difficult to track. It was found that the signal from the satellites in some directions could not be tracked even if no obstruction existed. The cause of this is believed to be as follows. Interference occurs between the signal received directly from the satellite and the reflected wave caused by the roof of the building. The interference changes according to satellite direction. To avoid this phenomenon, GPS antenna should be installed in a location as far away as possible from the objects that reflect electromagnetic waves.

GPS antenna Zenith

--- Satellite signal is attenuated.

Attenuation occur even if no obstruction exists.

Building

Reflected wave

Horizontal

Fig. 11. GPS antenna installation in Toshiba Fuchu Complex.

C. Effect of natural phenomenon The effects of natural phenomenon have been assessed.

Rain or snow is no problem. In October 2003, a powerful solar flare occurred and its negative impact on power systems and/or communication systems was of great concern throughout the world, also in Japan, a geomagnetic storm was

monitored from October 29 to 31. In this period, the stability of GPS signal receipt was monitored. As a result, 1PPS interruption did not occur and horizontal positioning accuracy was not degraded (5.31m standard deviation in 24 hours that was 6.16m under normal conditions) throughout the monitoring. Furthermore, the monitoring was performed for a given period of time when the war in Iraq is occured, however degradation was still not observed.

(a)normal condition (b)solar flare condition 24 hours from 3:15AM Oct.30 2003 24 hours from 3:00PM Mar.9 2001

Fig. 12. Example of reception monitoring result.

D. Monitoring result of GPS signal receiving in the event of satellite anomaly

A significant satellite anomaly occurred on 1 January 2004 and an interruption to the 1PPS signal occurred on almost all of the GPS receivers that we have supplied for various substations in Japan.

On January 1, a failure occurred in the atomic frequency standard on one of the GPS satellites (PRN23) and caused transmission of misleading information between approximately 6:33 pm and 9:18 pm (UTC) [8]. This anomaly affected GPS receivers over a large portion of the world. Although significant anomalies are believed to be a rare occurrence, the availability of the T-RAIM function, which we describe later, within the GPS receiver ensures that even under the most extreme conditions interruption to the positioning or 1PPS signal can still be avoided.

TABLE I MONITORING RESULT OF 1PPS SIGNAL AT SUBSTATIONS.

Monitoring place On the roof of relay room

in Substation A On the roof of test building

in Toshiba’s Fuchu Complex

On the roof of relay room in Substation B

On the roof of relay room in Substation C

Monitoring Period From 1 November 2001 To 25 September 2002

(Monitoring is suspended from 5 April to 22 May)

From 3 November 2001 To 3 July 2002

(Monitoring is suspended several times)

From 10 June 2002 To 27 November 2002

From 10 June 2002 To 27 November 2002

Total monitoring days 281 days 186 days 170 days 170 days The number of 1PPS pulse

interruption occurrence 225 Pulses 203 Pulses No interruption No interruption

Rate of interrupting time 9.3ppm 13ppm No interruption No interruption Maximum interruption

continued 22 seconds 9 seconds No interruption No interruption

GPS antenna type Normal type(Gain : min 25dB) High sensitive type(Gain : min 29dB) Length of coaxial cable 5D-FB 60m 3D-2V 10m

+ 5D-2V 17m 5D-FB 2m

+ 8D-FB 60m Parabola antenna exists

near the GPS antenna Coaxial cable is rather long

for GPS antenna gain. 275kV substation

Various transmission equipments exist.

Indoor substation among the residential section

V. THE METHOD FOR STABLE OPERATION OF GPS SYNCHRONIZING FOR POWER SYSTEM PROTECTION AND

CONTROL In the application of GPS synchronization to protection and

control systems, correct antenna installation and an appropriate GPS receiver set-up procedure is important if high reliability synchronization is to be achieved. In this section, several methods are described.

A. GPS Antenna location To avoid the loss of the GPS satellite signal, it is important

that the GPS antenna is installed in an appropriate position. Our investigation and recommendations based on the results obtained are described.

Following power-up, the GPS receiver must estimate the location of the GPS antenna by signal receipt from more than four satellites. After completing location estimation, the GPS receiver requires the signal from at least one satellite in order to output the 1PPS signal. Because satellites move, the number of satellites tracked changes throughout a day as shown in Fig. 13. Because the GPS satellite signal travels in a straight line obstructions such as buildings located close to the GPS antenna may prevent the receipt of signals from some of the satellites. For example, if an antenna is installed close to the side of a building, the number of satellites tracked may decrease to either 0 or 1, therefore interruption of the 1PPS signal output may occur. If the antenna is installed in a location that offers an unobstructed view of the sky such as the roof of a building, signals from more than 4 satellites can usually be received and it is of no consequence if signals from one or more of the satellites cannot be received due to a change of circumstance.

(a) Close to wall of building (b) On the roof of building Fig. 13. Change in number of tracked satellites.

The number of satellites in the direction above the

elevation angle dictated by the height of the obstructions around the GPS antenna is shown in Fig. 14.

GPS antenna

Building etc.

Mask

Calculate the number of satellite in this area

Angle

Elevation

Fig. 14. Condition of GPS antenna installation.

Even under the same masking conditions, the number of

satellite signals that can be received differs in accordance with the conditions of satellite operation. The availability of operational satellites is reported to be higher than 99 percent [9]. Fig. 15 shows the actual number of operational satellites totalled up from the status report published by the Navigation Center of the U.S. Coast Guard. In the figure, the thick line shows the total number of satellites. The line that changes frequently shows the real number of satellites taking into account satellites out-of-service for maintenance. Approximately 27 satellites have been available on average for the two and a half years up until July 2004.

Fig. 15. Operation status of GPS satellites.

As a result, it is recommended that GPS antennas are installed in locations that offer unobstructed views of the sky with an elevation angle of 15 degrees to the horizontal. If this is difficult, a location that offers the same viewing area of the sky is recommended.

Fig. 16 shows the measurement results obtained in terms of GPS signal receipt in a substation with GPS monitor. The white circle shows the satellites that could be tracked. As shown Fig. 16(b), even in substations located in mountainous regions such as hydro-power stations, the required view of the sky can be found and a sufficient number of satellite can be tracked.

N

W E

S (a)Substation at Open field (a)Substation in valley

N

W E

S

Fig.16. Example of monitoring result of receiving condition.

Fig. 17 shows the measurement results of a number of

satellite signals received in 31 different substations where GPS antennae have been installed to date. Although on occasions GPS antenna are installed in substations in mountainous regions signals from more than 4 satellites could be received in all cases and GPS antenna have been installed without any problems to date.

(Limited to eight by the specification of GPS receiver used in the test.)

Fig. 17. Number of tracked satellites monitored in substations.

B. The method for GPS application to protection relay In power system protection, highly reliable and precisely

synchronized current data between the ends of a transmission line can facilitate the application of line current differential relay systems to modern digital communication networks such as Synchronous Digital Hierarchy (SDH).

In this relay, it is required that the data sampling timings at both ends of the transmission line are synchronized reliably. If a synchronization error in data sampling occurs due to temporary loss of a satellite signal or incorrect timing synchronization, calculated current values using the sampling result of instantaneous data will be different from that calculated in the current differential relay installed at each end of the protected line and the current differential function may operate incorrectly.

As a countermeasure for temporary satellite signal loss, the method described as follows is useful. Each relay measures the time difference between the output of its own sampling oscillator and the GPS 1PPS 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. With this procedure, the results of interruption periods (shown in Table 1) observed in substations are acceptable for a differential relay.

In addition to the procedure described above relays applied to an actual power system and in commercial operation in the U.K also provide some unique GPS synchronization back-up modes to withstand longer periods of GPS signal loss.

Furthermore, the countermeasure for degradation of the GPS signal due to problems with satellites is important. The navigation message broadcast from satellites includes data on the health of all satellites. Therefore, problems with satellites can be detected at GPS receivers. But there is a possibility that the health data cannot be set to unhealthy immediately and the GPS receiver uses the signal from an unhealthy satellite, causing an erroneous timing solution.

To avoid this problem, T-RAIM (Time Receiver

autonomous integrity monitoring) has shown to be effective. TRAIM is a function of the GPS receiver that is used to detect an unhealthy satellite by using measurements from additional (redundant) satellites that are used to provide an over-determined navigation solution. If an unhealthy satellite is detected, the receiver 1PPS signal output is blocked by this function. If only one satellite is unhealthy, the unhealthy satellite is excluded from the solution and the 1PPS signal output can be maintained using measurements obtained from other available satellites. If T-RAIM is used, at least two satellites are needed for a 1PPS signal output following the first fix (fixing of first positioning after the receiver is powered-up). Although more satellites are needed if the TRAIM function is used, the relays have been able to operate without problems to date.

When a GPS satellite anomaly actually occurred on 1 January 2004, almost all of the GPS receivers we supplied to substations in Japan blocked their 1PPS signal output. We had been monitoring the 1PPS signal in our factory actually during this period and observed that the 1PPS signal could be output continually if T-RAIM is used.

VI. CONCLUSION A high reliability, high resolution synchronizing signal

distribution technique suitable for application to the entire substation system has been developed. This technique has already been widely applied in operational systems and protection relays. Results have been excellent to date.

A digital signal is transmitted over optical fiber for synchronization with high resolution. A signal encoding technique is used to solve the problem of incorrect timing detection caused by optical device deterioration and therefore high reliability synchronization has been achieved.

Long-term assessments of the stability of GPS signal receipt in a variety of substations have been undertaken and stable receipt of the GPS signal has been demonstrated. In addition, several methods have been recommended for consideration when GPS synchronization techniques are applied to protection and control systems. In particular, countermeasures have been described that are employed in the event of a loss of satellite signal and on the occurrence of satellite anomalies.

It was observed that synchronization signal output could be maintained even when a GPS satellite anomaly actually occurred if the T-RAIM function is used. T-RAIM is used in all of our line current differential relay as a powerful function to ensure reliability. By considering these methods, high reliability performance can be confirmed in the application of GPS synchronization to protection and control systems.

VII. ACKNOWLEDGMENT The authors gratefully acknowledge the contributions of

Kansai Electric Power Company for cooperating in long-term monitoring of GPS signal receiving in substations. We also

acknowledge the contributions of electric power companies in Japan for cooperating in monitoring in many substations.

VIII. REFERENCES [1] D. Itagaki, Y. Fuwa ”GPS based Time Synchronizing Signal

Distribution Method for Power System Protection / Control Systems and Field Experience”, 2004 National Convention Record IEE Japan, 281,(2004)

[2] D.Itagaki, K. Ohashi, M. Saga, I.Shuto, ”Development of High Resolution and High Reliability Time Synchronizing Signal Distribution Technique for Substation Systems”, IEE-DPSP’04, pp.714-717, (2004)

[3] D.Itagaki, Y.Shirota, K.Sekiguchi, “Field experiences and assessment of GPS synchronizing signal receiving for power system protection, control and monitoring”, 2004 Technical Meeting on Power Protective Relay IEE Japan,(2004)

[4] I. HALL, P. G. Beaumont, G. P. Baber, I. Shuto, M. Saga, K. Okuno, H. Ito, ”New Line Current Differential Relay using GPS Synchronization”, IEEE Bologna PowerTech Conference’03

[5] S. Imai, et al., “A Newly Developed Web-based Fault Locating Technology for Transmission Lines and Its Experience in the Field”, IEEE/PES T&D Conference Proceedings Vol.1, October ’02, pp.136-141.

[6] IRIG-STANDARD200-89, Telecommunications Group, Range Commanders Council, U.S.Army White Sands Missile Range, NM.

[7] IEEE Std 1344-1995, Standard for Synchrophasors for Power Systems [8] http://www.schriever.af.mil/GPSSUPPORTCENTER/ [9] http://www.navcen.uscg.gov/gps/geninfo/2001SPSPerformanceStandard

FINAL.pdf

IX. BIOGRAPHIES

Daiju Itagaki received his BS and ME degrees in engineering from Tokyo Institute of Technology, Tokyo Japan. He joined Toshiba in 1996, and is currently responsible for development of protection and control systems.

Kenichiro Ohashi received his B.S. degree in electrical engineering from Tohoku Gakuin university, Japan, and joined Toshiba in 1995.He is currently responsible for product development of protection and control systems as a quality assurance/testing engineer

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

Hachidai Ito (M '85) received his BS and ME degrees in electrical engineering from Kyoto University, Kyoto, Japan in 1979 and 1981 respectively. Also he received his MS degree in Computer Science from University of Maryland, College Park, Maryland USA in 1987. He joined Toshiba in 1981, and was working as a development engineer and a manager of Protection and Control Development Department. He is now a Chief Engineer in Power System Protection &Control and

is principally responsible for technology and overseas marketing of protection and control products in Toshiba Corporation. He is a member of IEEE, IEEJ and IEICE. Also he is a secretary of Japanese National Committee of IEC/TC95, a member of its 3 working groups, a member of CIGRE WG B3.05 and a member of several working groups in IEEE/PSRC.