GB2486684A

GB2486684A - Sampling synchronization method for digital protective relaying system

Info

Publication number: GB2486684A
Application number: GB201021746A
Authority: GB
Inventors: Youko Toda
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2010-12-20
Filing date: 2010-12-20
Publication date: 2012-06-27
Anticipated expiration: 2030-12-20
Also published as: GB2486684B; GB201021746D0

Abstract

A protective relaying system that optimizes a timing of a sampling signal by use of a signal from a GPS receiver is provided. In the protective relaying system, a delay time difference Î± is calculated from a time Tms between output of the sampling signal by a protective relay and receipt of data from an adjacent protective relay by the protective relay and a time Tsm between output of a sampling signal by the adjacent protective relay and receipt of data from the protective relay by the adjacent protective relay, and the thus-calculated delay time difference Î± is stored. When the GPS signal is abnormal, a correction unit included in the protective relaying system synchronizes the sampling signal to the sampling signal from the adjacent protective relay based on newly determined Tms and Tsm and the stored value Î±.

Description

DIGITAL PROTECTIVE RELAYING SYSTEM AND SAMPLING SYNCHRONIZATION

METHOD FOR DIGITAL PROTECTIVE RELAYING SYSTEM

TECHNICAL FIELD

[0001] The present invention relates to a power digital protective relaying system that performs synchronization of sampling signals by utilization of a GPS (Global Positioning System).

[0002] In a related-art protective relaying system utilizing a GPS signal, a timing difference between a reference signal of a predetermined period from a GPS receiver and a sampling signal of a protective relay is measured, and a correction is made to a frequency of the sampling signal according to the thus-measured timing difference. It is possible to synchronize sampling signals of all protective relays by making corrections to frequencies of the sampling signals of the respective protective relays.

[0003] In a case where a signal from the GPS receiver is lost, there has been proposed a technique for synchronizing the sampling signal according to a previously measured delay time of a data communication time between an adjacent protective relay and a receive timing of current data, (see; for instance, JP-A-2002-186 166).

[0004J In the related art digital protective relaying system utilizing a GPS signal, a correction is made to sampling signals of respective relays according to a reference signal from the GPS receiver.

[0005] Further, when a radio wave from a GPS satellite or a signal from the GPS receiver is lost, sampling signals are synchronized according to a previously measured delay time of a communication time of an adjacent protective relay and a receive timing of current data. The related art technique is provided in relation to a method based on a premise that delay times occurring during outgoing communication and incoming communication between respective adjacent protective relays are equal. Therefore, there is a problem of the technique being incapable of addressing a case where a communication path for outgoing communication differs from a communication path for incoming communication, which results in a change in the delay time.

SUMMARY

[0006] Accordingly, it is an aspect of the present invention to assure a high degree of synchronization by a GPS signal and also to synchronize sampling times even when a communication delay time of outgoing communication and communication delay time of a incoming communication between an adjacent protective relay differs when an GPS is in an abnormal state.

[0007] According to an embodiment of the present invention, there is provided a protective relaying system that optimizes a timing of a sampling signal by use of a signal from a GPS receiver. In the protective relaying system, a delay time difference a is calculated from a time Ims between output of the sampling signal by a protective relay and receipt of data from an adjacent protective relay by the protective relay and a time Tsm between output of a sampling signal from the adjacent protective relay and receipt of data from the protective relay by the adjacent protective relay, and the thus-calculated delay time difference a is stored. When the GPA signal is abnormal, a correction unit included in the protective relaying system synchronizes the sampling signal to the sampling signal from the adjacent protective relay based on newly determined Tms and Tsm and the stored value a.

[00081 According to the above-described configuration, when the signal from the GPS receiver has become abnormal, it possible to correct the sampling signal by a simple method without a great change in calculation method. Further, even when a data communication delay time that occurs during exchange of data between adjacent protective relays change between outgoing communication and incoming communication, accurate correction of the sampling signal can be achieved;

BRIEF DESCRIPTION OF DRAWINGS

[0009] Fig. 1 is a block diagram illustrating a configuration of a first embodiment of the present invention; Fig. 2 (2A and 2B) is a drawing illustrating sampling synchronization processing I of the first embodiment of the present invention; Fig. 3 is a drawing illustrating Flowchart I of the first embodiment of the present invention; Fig. 4 is a drawing illustrating Flowchart 2 of the first embodiment of the present invention; Fig. 5 is a drawing illustrating Flowchart 3 of the first embodiment of the present invention; Fig. 6 is a drawing illustrating Flowchart 4 of the first embodiment of the present invention; Fig. 7 is a block diagram illustrating a configuration of a second embodiment of the present invention; Fig. S is a drawing illustrating Flowchart 5 of the second embodiment of the present invention; Fig. 9 is a drawing illustrating Flowchart 6 of the second embodiment of the present invention; Fig. 10 is a drawing illustrating Flowchart 7 of the second embodiment of the present invention; Fig. 11 is a block diagram illustrating a configuration of a third embodiment of the present invention; Fig. 12 (12A, 126 and 12C) is a view illustrating sampling synchronization processing 2 of a fourth embodiment of the present invention; Fig. 13 (13A, 136 and 13C) is a view illustrating sampling synchronization processing 3 of the fourth embodiment of the present invention; Fig. 14 is a drawing illustrating Flowchart 8 of the fourth embodiment of the present invention; Fig. 15 is a drawing illustrating Flowchart 9 of the fourth embodiment of the present invention; Fig. 16 is a drawing illustrating Flowchart 10 of the fourth embodiment of the present invention; and Fig. 17 is a drawing illustrating Flowchart 11 of the fourth embodiment of the present invention.

DETAILEDDSCRIPTION OF EMBODIMENT$ First Embodiment 10010] Protective relays, disposed at both ends of a power transmission line that extends over; for instance, kilometers to tens of kilometers, measure current vectors of the power transmission line and compare current vectors measured at both ends of the power transmission line with each other. When a resultant difference exceeds a predetermined value, a protective relaying system determines occurrence of a failure and disconnects the faulty section from an electric power system. Since current vectors achieved at remote locations are compared with each other, a sampling signal that is to serve as a reference is important. A reference signal generated from a OPS signal has recently been utilized as a sampling signal.

[0011] A digital protective relay employs a technique for digitizing an analogue value on a per sampling time according to a PCM (Pulse Code Modulation) scheme. A current vector transmitted in the form of a digital signal from another end is compared with a current vector measured at a target end at the same time. When a difference between the vectors has exceeded a predetermined value, a fault is determined to have arisen, and the fault section is shut off.

[0012] Fig. 1 is a block diagram illustrating a configuration of the first embodiment of the present invention.

[0013] The digital protective relaying system 1 is constructed by connecting a first digital protective relay 101 to a second digital protective relay 201 that are adjacent to each other. Hereinafter, as a matter of convenience, the first digital protective relay 101 is called a slave station, and the second digital protective relay 201 is called a master station. However, they can also be called inversely.

100141 An explanation is first given to operation of the slave station performed when a GPS signal is normal. A normal GPS signal signifies a case where a GPS signal 138 is properly transmitted from the GPS receiver to the slave station 101. The GPS signal 138 herein designates a signal periodically transmitted from the GPS receiver to the slave station 101 for synchronization purpose.

[0015] In addition to including a case where a radio wave from a GPS satellite has not appropriately arrived at the earth, an abnormal GPS signal encompasses a failure of the GPS receiver, a case where an abnormal exists in a signal line for transmitting a signal from the GPS receiver, and the like.

[0016] The slave station 101 has an ND conversion unit 102 that converts analogue data 131 pertaining to an electrical quantity of the target end into digital data and a data calculation unit 103 that receives from the ND conversion unit 102 first electrical quantity data which are digital data pertaining to the electrical quantity of the target end, processes the received data into transmission data, and passes the transmission data to a data communication unit 105. The data communication unit 105 transmits the first electrical quantity data to the master station via a first data communication path; receives from the master station second electrical quantity data pertaining to an electrical quantity of the other end via a second data communication path; and passes the thus-received second electrical quantity data to the data calculation unit 103. The data calculation unit 103 compares the first electrical quantity data with the second electrical quantity data. When an absolute value of the difference is greater than a predetermined value, a trip signal 132 is output via an output unit 104.

[0017] A sampling signal output unit A 106 includes a internal clock. Upon receipt of a GPS signal 138, the sampling signal output unit A 106 corrects a signal period determined by the internal clock to a correct period by a correction value Kf. A first sampling signal 133 is fed to the ND converter 102, the data calculation unit 103, and the data communication unit 105, thereby synchronously performing AID conversion of analogue data and data transmission.

[0018] Likewise, the master station 201 also includes an ND conversion unit 202, data communication unit 205, data calculation unit 203, and sampling signal output unit A 206.

[0019] Like the first sampling signal 133, a second sampling signal 233 output from the sampling signal output unit A 206 is also synchronized by the GPS signal. Hence, the slave station 101 and the master station 201 synchronously perform ND conversion of analogue data and data transmission.

[0020] In the slave station 101, delay a time difference calculation unit 107 receives from the data communication unit 105 information about a delay time of data communication between the slave station and an adjacent master station.

[0021] The delay time difference calculation unit 107 receives data pertaining to a second data communication delay time (Tdl) between output of the first sampling signal from the slave station and receipt of, via the second data communication path, the second electrical quantity data transmitted by the master station. The delay time difference calculation unit 107 also receives, via the data communication unit 105, data pertaining to a first data communication delay time (Td2) between output of the second sampling signal from the master station and receipt of, via the first data communication path, the first electrical quantity data transmitted from the slave station. Further, a delay time difference (cc) is calculated from the first data communication delay time and the second data communication delay time (Td2 and IdI), and a calculation result is stored in a storage unit 108. The first data communication path that is an up path from the slave station to the master station sometimes differs from the second data communication path that is a down path from the master station to the slave station.

The first data communication delay time and the second data communication delay time, which exist between start of transmission and completion of receipt, often change from the up path to the down path. Hence, a delay time difference (a) exists.

[00221 When the GPS signal 138 has become abnormal, the first sampling signal output unit A 106 outputs the first sampling signal 133 while maintaining a correction value Kf that was acquired when the GPS signal was determined to be normal by reference to the internal clock signal. At this time, there is a possibility that a difference will arise between the timing of the first sampling signal 133 in the slave station 101 and the timing of the second sampling signal 233 in the master station 201 as time elapses.

[0023] When the GPS signal 138 has become abnormal, the timing difference calculation unit 110 receives, from the data communication unit 105, a fourth data communication delay time (Tms) between output of the first sampling signal from the slave station and receipt of the second electrical quantity data transmitted by the master station. The timing difference calculation unit 110 also receives, via the data communication unit 105, specifics of data pertaining to a third data communication delay time (Tsm) between output of the second sampling signal from the master station and receipt of the first electrical quantity data transmitted by the slave station, the specifics of the data being transmitted from the data communication unit 205 of the master station.

[0024] The timing difference calculation unit 110 receives, from the delay time difference calculation unit 107, the delay time difference cc that was calculated when the GPS signal was normal and that was stored in the storage unit 108. The timing difference calculation unit 110 calculates from the data a timing difference (AT) between the sampling signal of the slave station 101 and the sampling signal of the master station 201. According to the thus-calculated timing difference (AT), first correction unit 111 transmits a first correction signal 137 to the sampling signal output unit A 106 and synchronizes the first sampling signal 133 output from the sampling signal output unit A 106 to the second sampling signal 233 of the master station 201.

[0025] Even when the GPS signals 138 and 238 have become abnormal, the first sampling signal 133 can be synchronized to the second sampling signal 233 through processing similar to that mentioned above.

[0026] Fig. 2 is a drawing illustrating sampling synchronization processing 1 of the first embodiment of the present invention.

[0027] Calculation of the data communication delay times, the delay time difference a and calculation of the timing difference AT are hereunder described.

[00281 Fig. 2A shows data transmission and receipt timing acquired when a signal from the GPS receiver is normal and when the master station 201 and the slave station 101, which are adjacent protective relays, coincide with each other in terms of output timing of a sampling signal.

[0029J Upward arrows denote sampling signals in the respective stations. Electric quantities of the respective stations sampled in synchronism with the sampling signals are transmitted. in addition to including the electric quantities of the respective stations acquired at the sampling timings, the data exchanged between the master station and the slave station include data, like information about a data communication delay time, a serial number given to data from a predetermined point in time, an absolute time, etc., at a required frequency.

[00301 When the first data communication path from the slave station to the master station differs from the second data communication path from the master station to the slave station, a data communication delay time between start of transmission and completion of receipt sometimes changes from the up path to the down path.

[0031] Since the sampling time of the master station and the sampling time of the slave station coincide with each other, the first data communication delay time 1d2 between the slave station and the master station (of the up path) and the second data communication delay time Tdl between the master station and the slave station (of the down path) can be correctly measured so long as the receiving side measures a time elapsed from the timing of the sampling signal until a data receipt time. Therefore, a difference a between the data communication delay time of the up path and the data communication delay time of the down path is obtained by Equation 1.

[0032] [Equation 1] a = Td2-Tdl [0033] Fig. 2B shows data transmission and receipt timing achieved when the GPS signal is abnormal and when a timing difference AT exists between the sampling signal of the master station and the sampling signal of the slave station.

[00341 Only a receiving station can measure a receipt time of transmission data from another station. Therefore, a time elapsed from when a sampling signal is output from the receiving station until when receipt of communication data is completed is measured by the receiving station, as the third data communication delay time Tsm in connection with the (up) path from the slave station to the master station and as the fourth data communication delay time Tms in connection with the (down) path from the master station to the slave station. These data include the timing difference AT between the sampling signal of the master station and the sampling signal of the slave station. Therefore, the communication delay times Tms and Tsm can be expressed as follows: [0035] [Equation 2] Tms = AT + Tdl [0036] [Equation 3] Tsm = Td2 -AT [0037J from Equations, 2, and 3 AT(Tms-Tsm +Td2-Tdl)/2 [Equation 4] :. AT = (Tms -Tsm + a) / 2 (0038] Consequently, a delay time difference a is calculated from the first data transmission delay time Td2 and the second data communication delay time Tdl that are obtained when the GPS signal is normal. The timing difference AT between the sampling signal of the master station and the sampling signal of the slave station can be determined from the delay time difference a, and further, from the third data communication delay time Tsm and the fourth data communication delay time Tms which are measured by the respective stations after the GPS signal has become abnormal.

[0039] The sampling signal of the master station and the sampling signal of the slave station can be synchronized by shifting the output of the sampling signal output unit A 106 of the slave station by a value of AT.

[0040] Fig. 2 illustrates an example in which the respective stations alternately transmit data once every two sampling signals. However, the respective stations may transmit data every time for each sampling signal.

[0041] Procedures employed when each of the stations transmits data every time for each sampling signal are described hereinafter.

[0042] Fig. 3 is a drawing illustrating Flowchart I of the first embodiment of the present invention.

[0043] The digital protective relaying system of the first embodiment is made by connecting the slave station 101 to the master station 201. Operation of the slave station 101 is described hereinafter.

[0044] The flowchart of Fig. 3 shows a case where a microcomputer controls functions of the respective blocks of the slave station 101 shown in Fig. 1. Equivalent processing can be performed even when a PLD (Programmable Logic Device) is used in stead of the microcomputer.

[0045] Step 500 shown in Fig. 3 shows start of interrupt processing in which an interrupt occurs as a result of receipt of the GPS signal 138 from the GPS receiver, to thus start a program.

[00461 In step 501, a time interval Pgps between a time Tgps(n-1) when a previous OPS signal is received and a time Tgps(n) when a current GPS signal is received is compared with a predetermined sampling signal period Pclk set in the internal clock.

The correction value Kf used for correcting the period of the internal clock is calculated by the following equation, and processing proceeds to step 510.

[0047] [Equation 5] Kf = (PclklPgps)-1 [0048] Processing pertaining to steps following step 510 shows procedures for storing in memory a period correction value Kf of the internal clock while dividing the value Kf into a fixed correction value Kfs and a variable correction value Kfv.

Calculation and storage of Kfs and Kfv are performed every time a predetermined period Tf elapses. For instance, If = I sec., calculation and storage are performed every one second.

100491 In step 510, a determination is made as to whether or not a predetermined time If has elapsed since the previous Kfs was updated. When the predetermined time Tf has not yet elapsed, processing proceeds to step 516.

100501 When the predetermined time If has elapsed, Kfs is read from the memory in step 511. In step 512, a difference (Kf -Kfs) between Kf calculated in step 501 and Kfs read from the memory is calculated. When a calculation result is positive, processing proceeds to step 513. When the calculation result is zero, processing proceeds to step 515. When the calculation result is negative, processing proceeds to step 514. In steps 513 and 514, only KIsb that is a very small value as compared with Kfs; for instance, I ppm, is added to or subtracted from Kfs, thereby updating Kfs.

[00511 For instance, the correction value Kf is added to Kfs by I ppm every second, whereby the correction value Kf can be expressed as a sum of the fixed correction value Kfs and the variable correction value Kfv as indicated by Equation 6.

[0052] [Equation 6] Kf = Kfs + Kfv [0053] if Kfs and Kfv are updated after elapse of a sufficient time, there will be calculated the fixed correction value Kfs for correcting a predetermined proportion of difference between a signal produced from the internal clock and the reference signal produced from the GPS signal. There will also be separately calculated the variable correction value Kfv for correcting ever-changing fluctuations, such as an ambient temperature, a voltage, humidity, and atmospheric pressure, and fluctuations unique to a digital relay. The values Kfs and Kfv can be stored in memory.

[0054] In step 515, Kfv is calculated by subtracting the updated Kfs from Kf (Kf -Kfs). Kfs and Kfv are saved in memory, and processing proceeds to step 516.

[0055] In step 516, a determination is made as to whether or not the absolute value of Kf is less than 0.1. When the absolute value is 0.1 or more, the correction value Kf is excessive and determined to be untrustable. Processing proceeds to step 519, where interrupt processing is terminated.

[00561 The determination value 0.1 may also be another value, such as 0.01,1 and is determined in light of a value that an actual relay can take.

[0057] When the absolute value of Kf is less than 0.1 the correction value Kf is determined to be trustable. In step 517, a GPS signal abnormal timer is cleared. in step 518, a GPS normal counter is incremented, and interrupt processing is terminated in step 519.

100581 Words "GPS signal normal timer," "GPS signal normal flag," "GPS signal abnormal timer," and "GPS signal abnormal flag" are used in steps of the flowcharts S shown in Figs. 3 through 5. They designate counters and flags used for determining whether a signal from the GPS receiver is normal or abnormal.

[0059] Fig. 4 is a drawing illustrating Flowchart 2 described in relation to the operation of the slave station 101 of the first embodiment of the present invention.

[0060J When the time measured by the internal clock after setting of output timing of the sampling signal has elapsed, a timer interrupt occurs, whereupon processing pertaining to step 540 starts.

[0061] The timer interrupt is set for outputting a predetermined sampling timing signal by the internal clock. For instance, when sampling is performed every 30-degree electrical angle for 60 Hz, a timer interrupt is invoked at 720 Hz (every 1.39 ms).

10062] During interrupt processing, the sampling signal 133 is first output in step 541. A value is determined by multiplying a predetermined sampling signal output period Pclk by (1 + Kfl, through use of the correction value Kf that has been calculated by comparison with the GPS signal. In order to set the next timer to be started, the value is set in the timer in step 542. Thereby, a sampling signal substantially synchronized with the signal from the GPS receiver can be produced next time.

[0063] In step 551, the electrical quantity data of the slave station subjected to ND conversion are stored along with a serial number. In step 552, the data are transmitted to the master station via the data communication unit. Subsequently, in step 553 a slave station data counter is incremented, thereby preparing for storage of the next data.

[0064] In step 561, the GPS signal abnormal timer is incremented. Incrementing the timer in step 561 is performed at an interval between generation of a sampling signal and generation of a subsequent sampling signal. When sampling is performed at 30-degree electrical angle for 60 Hz, the timer is incremented at a frequency of 720 Hz (every 1.39 ms).

[0065] When the GPS signal can be properly received, the GPS signal abnormal timer is cleared in step 517 in Fig. 3 every time the GPS signal is received at timing of 720 Hz. Hence, a count value is not increased much.

[0066] In step 562, a determination is made as to whether or not the GPS signal abnormal timer is Te2 or more. For instance, if Te2 is 720, the signal from the GPS receiver is determined not to be properly received for one second or more, When an increment value of the GPS signal abnormal timer is Te2 or more, processing proceeds to step 565, where the GPS signal abnormal flag is set. Processing then proceeds to step 566.

[0067] When the value of the GPS signal abnormal timer is less than Te2, processing proceeds to step 563, where a determination is made as to whether or not the value is Tel or more. For instance, if Tel is 72, a determination is made as to whether the value is no smaller than 0.1 second and no greater than I second. When the OPS signal falls in the range, processing proceeds to step 564, where the OPS signal normal counter is cleared. Processing then proceeds to step 566.

[00681 When the value of the GPS signal abnormal timer is less than Tel, processing proceeds directly to step 566.

100691 In step 566, a determination is made as to whether or not the value of the GPS normal counter is Cn or more. For instance, if Cn is 720, whether a normal GPS signal is received for 1 second or more can be determined. If the value of the GPS normal counter is Cn or more, the OPS signal normal flag is set in step 568.

Subsequently, the GPS abnormal flag is cleared in step 569, and interrupt processing is terminated in step 570.

[00701 In step 566, when the value of the GPS normal counter is less than Cn, the reliability of the GPS signal is low. Therefore, in order to show that the GPS signal is not appropriate for use, the GPS signal normal flag is cleared in step 567, and interrupt processing is terminated in step 570.

[0071] Processing procedures described by reference to Figs. 3 and 4 also apply to operation of the master station 201.

100721 Figs. 5 and 6 are drawings illustrating Flowcharts 3 and 4 described in connection with the operation of the slave station 101 of the first embodiment of the present invention.

[0073] Flowchart 3 of Fig. 5 is first described. Interrupt processing pertaining to a case where the slave station 101 has received communication data 135 from the master station 201 is started in step 601.

[0074] In step 602, a check is made as to whether or not a GPS signal abnormal flag is set. When the GPS signal abnormal flag is not set, processing proceeds to step 612.

100751 When the GPS signal abnormal flag is set in step 602, processing proceeds to step 603. In step 603, a determination is made as to whether or not the absolute value of the correction value Kf is less than a predetermined value Ki. When the absolute value of the correction value is K1 or more, the absolute value of the correction value is large. Hence, when the GPS signal is abnormal, the sampling signal of the master station and the sampling signal of the slave station are considered to cause a difference. Hence, Tdl, Td2, and a are not updated, and processing proceeds to step 621.

[0076J When the absolute value of the correction value Kf is less than KI in step 603, processing proceeds to step 604. In step 604, a time Ira is determined by a function Fl of the absolute value of the correction value Kf. In step 605, a determination is made as to whether or not the timer value of the GPS signal abnormal timer is smaller than Tra. The function Fl may also be determined in such a substantially, inversely proportional way that the time Tra becomes smaller as the absolute value of the correction value Kf becomes greater. Alternatively, the function Fl can also be specified so as to plot a discontinuous curved line or a discontinuous straight line on a map.

[0077] In the embodiment, the predetermined value to be compared with the timer value is taken as Tra, and Tra is specified as the function of the absolute value of the correction value Kf. However, if the predetermined value is specified as a fixed value, a necessity for setting a map, or the like, is lessened and can be simply realized.

[0078J When the timer value is Ira or more, a sufficient time is considered to have already elapsed since the GPS signal became abnormal, and a difference might have arisen between the sampling signal of the master station and the sampling signal of the slave station. Hence, processing proceeds to step 621 without updating Tdl, Td2, and a.

[0079] When the timer value is smaller than Ira in step 605, a time elapsed since the GPS signal became abnormal is determined to be small, and processing proceeds to step 606.

[0080] In step 606, the variable correction value Kfv, among the correction values generated from the internal clock signal with reference to the signal from the GPS receiver, is read from the memory. In step 607, a determination is made as to whether or not the thus-read variable correction value Kfv is less than a previously-determined predetermined value K2. When the absolute value of the variable correction value Kfv is K2 or more, there is a conceivable high possibility that the sampling signal of the master station will shift from the sampling signal of the slave station. Hence, processing proceeds to step 621 without updating Tdl, Td2, and a.

[0081] In step 607, when the absolute value of the variable correction value Kfv is less than K2, processing proceeds to step 608. In step 608, a time Trb is determined by a function F2 of the absolute value of the variable correction value Kfv. In step 609, the time Trb is compared with the GPS signal abnormal timer, to thus determine whether or not a timer value of the GPS signal abnormal timer is smaller than the time Trb. The function F2 may be determined in such a substantially, inversely proportion way that, as the absolute value of the variable correction value Kfv becomes greater, the time Trb becomes smaller. Alternatively, the function F2 can also be specified so as to plot a discontinuous curved line or a discontinuous straight line on a map.

[0082] In the embodiment, the predetermined value to be compared with the timer value is taken as Trb, and Trb is specified as the function of the absolute value of the variable correction value Kfv. However, if the predetermined value is specified as a fixed value, a necessity for setting a map, or the like, is lessened and can be simply realized.

[0083] When the timer value is Trb or more, a sufficient time is considered to have already elapsed since the GPS signal became abnormal, and a difference might have arisen between the sampling signal of the master station and the sampling signal of the slave station. Hence, processing proceeds to step 621 without updating IdI, Td2, and a.

[0084] In step 610, a check is made as to whether or not a change has arisen in the data communication path. What is simultaneously exchanged between the slave station and the master station includes data pertaining to a data communication delay time and a data communication path being used as well as data pertaining to a current quantity sampled at predetermined timing.

100851 When the data show that a change has arisen in the data communication path, processing proceeds to step 612. On the contrary, when a change in data communication path is not informed, processing proceeds to step 611, where a determination is made as to whether or not a great change has occurred in the data communication delay time. Specifically, the actually measured data communication delay times Ism and Tms are compared with the times Td2 and Tdl measured when the GPS signal was normal. If any one of absolute values of the differences is the predetermined value 1k or more, a great change is determined to have arisen.

100861 When no great change has occurred in the data communication delay time, processing proceeds to step 621.

[00871 When a great change has occurred in the data communication delay time, the up or down data communication path is determined to be changed, and processing proceeds to step 612.

[0088] Flowchart 4 of Fig. 6 is described hereinafter.

[0089] Steps 611 and 612 in Fig. 5 follow steps 611 and 612 in Fig. 6. In steps subsequent to step 612A, Idi, 1d2, and a are updated on the premise that the sampling signal of the master station and the sampling signal of the slave station are maintained in a substantially synchronous state.

10090] In step 612A, the mth master station electrical quantity data transmitted from the master station and the first data communication delay time Td2 are stored in the memory.

100911 In subsequent step 613, a time elapsed from when the slave station outputs the first sampling signal until when the data are received from the master station is calculated. A calculation result is stored as the second data communication delay time Tdl in the memory.

[0092] In subsequent step 614, a delay time difference cx is determined from Idi and Td2 by Equation 1, and the thus-determined time difference is stored in the memory. Processing then proceeds to step 630.

[0093] In step 621A, the received mth master station electrical quantity data are stored in the memory. Further, the third data communication delay time Ism between output of the sampling signal and receipt of communication data from the slave station measured by the master station has already been transmitted from the master station.

The received data Tsm are also stored in the memory.

10094] In step 622, the fourth data communication delay time Tms between output of the first sampling signal and completion of receipt of communication data from the mt communication master station is calculated in the slave station, and a calculation result is stored in the memory.

[00951 In subsequent step 623, a timing difference AT between the sampling signal of the master station and the sampling signal of the slave station is calculated by Equation 4, and a calculation result is stored in the storage unit. Processing then proceeds to step 624.

[00961 In step 624, output timing of the sampling signal 133 is shifted by use of the timing difference AT. By shifting of the timing by AT, a difference between the sampling timing of the master station and the sampling timing of the slave station is corrected, so that the sampling timings of both of the stations can be synchronized.

100971 Subsequently, in step 630, the electrical quantity data with the latest, identical serial number "m" stored in memory of the master station and the latest, identical serial number "m" stored in memory of the slave station are compared with each other. When an absolute value of the difference is greater than the predetermined value K, processing proceeds to step 632, where the power system is shut off, to thus protect the relay. In step 639, interrupt processing ends.

10098] In step 631, when the absolute value of a difference between the ni" electrical quantity of the master station and the mth electrical quantity of the slave station is less than the predetermined value, processing directly proceeds to step 639, where interrupt processing ends.

10099] The above has provided an explanation about processing of the first embodiment including making a determination by use of the correction value Kf, the variable correction value Kfv, or functions of the values after the signal from the GPS receiver has became abnormal, thereby allowing updating of Tdl, Td2, and a. The processing is applicable not only to the first embodiment but also to second and third embodiments, which will be described later, through the same procedures.

1001001 In the first embodiment of the present invention, when the signal from the GPS receiver has become abnormal, the sampling signals can be corrected by a simple method without involvement of a large change in the calculation method.

Moreover, even when a data communication delay time that occurs during exchange of data between adjacent protective relays changes from outgoing communication to incoming communication, a correction can accurately be made to the sampling signals.

[001011 Further, even in a case where the OPS signal is abnormal, if the timing difference between the sampling signal of the master station and the sampling signal of the slave station can be estimated to be small, the values of the up data communication delay time 1d2, the down data communication delay time Tdl, and the value of the delay time difference a saved in the memory can be updated according to changes in these values. Even when a change has occurred in the data communication path, the change can thereby be addressed. A correction can be correctly made when a timing difference has subsequently arisen between the sampling signal of the master station and the sampling signal of the slave station.

[00102] In addition, as indicated by step 610 shown in Fig. 5, a change in data communication path is estimated from the data communication path information concurrently transmitted and received during transmission and receipt of the electrical quantity data performed between the master station and the slave station. Even when the GPS signal is abnormal, the values of the up data communication delay time Td2, the down data communication delay time Tdl, and the value of the delay time difference a saved in the memory can be updated according to changes in these values, so long as other conditions are satisfied. Even when a change has occurred in the data communication path, the change can thereby be addressed. A correction can be correctly made when a timing difference has subsequently arisen between the sampling signal of the master station and the sampling signal of the slave station.

[00103] Further, when a change in data communication path is determined from an amount of change in data communication delay time as indicated by step 611 shown in Fig. 5 and when the amount of change exceeds the predetermined value, the values of the up data communication delay time Td2, the down data communication delay time Tdl, and the value of the delay time difference a saved in the memory can be updated according to changes in these values. Even when a change has occurred in data communication path, the change can thereby be addressed. A correction can be accurately made when a timing difference has subsequently arisen between the sampling signal of the master station and the sampling signal of the slave station.

[00104] Moreover, as indicated by step 608 shown in Fig. 5, the timing difference existing between the sampling signal of the master station and the sampling signal of the slave station can be estimated to be small until a predetermined time elapses since the GPS signal became abnormal. Hence, the values of the up data communication delay time Td2, the down data communication delay time Idi, and the value of the delay time difference a saved in the memory can be updated according to changes in these values. Even when a change has occurred in data communication path, the change can thereby be addressed, A correction can be accurately made when a timing difference has subsequently arisen between the sampling signal of the master station and the sampling signal of the slave station.

[00105J As indicated by step 603 shown in Fig. 5, if an absolute value of the correction value Kf produced by correcting the period Pclk of the signal generated by the internal clock of the digital protective relay by use of the period Pgps generated from the GPS signal is smaller than the predetermined value KI, the timing difference between the sampling signal of the master station and the sampling signal of the slave station can be estimated to be small. Therefore, the values of the up data communication delay time Td2, the down data communication delay time Tdl, and the value of the delay time difference a saved in the memory can be updated according to changes in these values. Even when a change has occurred in data communication path, the change can thereby be addressed. A correction can be accurately made when a timing difference has subsequently arisen between the sampling signal of the master station and the sampling signal of the slave station.

[00106] As indicated by steps 604 and 605 shown in Fig. 5, the determination value Tra is determined by the function Fl (IKfI) of the absolute value of the correction value Kf that is obtained by correcting the period Pclk of the signal generated by the internal clock of the digital protective relay by the period Pgps acquired from the GPS signal.

The timing difference between the sampling signal of the master station and the sampling signal of the slave station can be estimated to be small until the time elapsed since the GPS signal became abnormal comes to Tra or more. Hence, the values of the first up data communication delay time Td2, the second down data communication delay time Tdl, and the value of the delay time difference a saved in the memory can be updated according to changes in these values. Even when a change has occurred in data communication path, the change can thereby be addressed. A correction can be accurately made when a timing difference has subsequently arisen between the sampling signal of the master station and the sampling signal of the slave station.

[00107] As indicated by step 607 shown in Fig. 5, the signal generated by the internal clock of the digital protective relay is compared with the signal produced from the GPS signal. When the absolute value of the variable correction value Kfv of the calculated correction value Kf is smaller than a predetermined value K2, the timing difference between the sampling signal of the master station and the sampling signal of the slave station can be estimated to be small. Hence, the values of the up data communication delay time Td2, the down data communication delay time Tdl, and the value of the delay time difference a saved in the memory can be updated according to changes in these values. Even when a change has occurred in data communication path, the change can thereby be addressed. A correction can be accurately made when a timing difference has subsequently arisen between the sampling signal of the master station and the sampling signal of the slave station.

[00108] As indicated by steps 608 and 609 shown in Fig. 5, the determination value Trb is determined by the function F2(IKf) of the absolute value of the variable correction value Kfv of the correction value Kf that is calculated by a comparison of the signal generated by the internal clock of the digital protective relay with the signal produced from the GPS signal. The timing difference between the sampling signal of the master station and the sampling signal of the slave station can be estimated to be small until the time elapsed since the GPS signal became abnormal comes to Trb or more. Hence, the values of the up data communication delay time Td2, the down data communication delay time Tdl, and the value of the delay time difference a saved in the memory can be updated according to changes in these values. Even when a change has occurred in data communication path, the change can thereby be addressed. A correction can be accurately made when a timing difference has subsequently arisen between the sampling signal of the master station and the sampling signal of the slave station.

Second Embodiment [00109] Fig. 7 is a block diagram illustrating a configuration of the second embodiment of the present invention.

[00110] A digital protective relaying system 2 is built by connection of a first digital protective relay 181 and a second digital protective relay 281 that are adjacent to each other.

[00111] The first digital protective relay 181 is called a slave station, and the second protective relay 281 is called a master station; however, they can also be called inversely, as in the first embodiment.

[00112] In relation to functional blocks in the slave station 181 and the master station 281, blocks having the same functions as those described in connection with the first embodiment are assigned the same reference numerals.

[00113] Explanations are given to differences between the present embodiment and the first embodiment by comparison with the first embodiment. In the first embodiment, the sampling signal output unit A 106 has the internal clock and receives the OPS signal 138, makes a correction to the GPS signal, and outputs a sampling signal. As indicated by the flowchart shown in Fig. 4, the sampling signal is produced by a timer interrupt caused by the internal clock.

[00114] In the second embodiment, as shown in Fig. 7, the foregoing internal clock is present in a backup reference signal generation unit 114. An output of the backup reference signal generation unit 114 generated by taking the internal clock as a reference is corrected by second correction unit 115 that receives the OPS signal 138 via a reference signal generation unit 113 and that corrects the GPS signal. Like the first embodiment, a correction is made by the correction value Kf.

[00115] The output of the backup reference signal generation unit 114 is selected by a switching unit 112 only when the OPS signal is abnormal, and the thus-selected output is fed to a sampling signal output unit B 116. However, when the GPS signal is normal, the output of the backup reference signal generation unit 114 generated from the internal clock is not selected by the switching unit 112, so that the sampling signal is not affected. The present embodiment differs from the first embodiment in this respect.

[00116] Fig. 8 is a drawing illustrating Flowchart 5 of the second embodiment of the present invention.

[00117] The following flowchart provides explanations about a case where respective functions of a block diagram shown in Fig. 7 are implemented by software.

[00118] The digital protective relaying system of the second embodiment is built by connecting the slave station 181 to the master station 281, and operation of the slave station 181 is principally described.

[00119] Fig. 8 differs from Fig. 3 only in that step 502 is added so as to follow step 501 in Fig. 3 illustrating Flowchart 1 of the first embodiment of the present invention.

[00120] In step 500 shown in Fig. 8, there is started interrupt processing in which a program starts when an interrupt is caused as a result of receipt of the GPS signal 138 from the GPS receiver.

[00121] In step 501, after the period correction value Kf of the internal clock has been calculated, the sampling signal 133 is output in step 502. The output of the sampling signal acts as a trigger, and a sampling signal interrupt shown in Fig. 10 is requested as interrupt processing attributable to an external signal.

(00122] In steps subsequent to step 510 following step 502, processing is the same as processing that shown in Fig. 3 that has already been described in connection with the first embodiment, and hence its explanation is omitted.

[00123] Fig. 9 is a drawing illustrating Flowchart 6 of the second embodiment of the present invention.

[00124] The built-in internal clock in the backup reference signal generation unit 114 causes a timer interrupt every time a preset timer value elapses, whereupon processing pertaining to step 741 is started. The timer interrupt is for generating a sampling signal in place of the GPS signal when the OPS signal is abnormal. For instance, when a sampling signal is generated every 30-degree electrical angle for 60 Hz, a timer interrupt is caused at a frequency of 720 Hz (every 1.39 ms).

100125] First, in order to set the next startup timer in step 742, the GPS signal is compared with the predetermined sampling signal output period Pclk in interrupt processing, and a value produced by multiplying (1 + Kf) by the correction value Kf calculated by comparison with the OPS signal is set in the timer. A timer interrupt can thereby be caused next time substantially in synchronism with the signal from the GPS receiver.

100126] In step 743, when a difference between the current time and a time at which the previous sampling signal was output exceeds 1.5 times of the sampling period, the GPS signal is determined to be interrupted. In step 744, a sampling signal is output, and the interrupt ends in step 749.

[001271 In step 743, when the current time has not elapsed the sampling signal output time by 1.5 x Pclk, processing pertaining to step 744 is skipped, and the interrupt is completed.

100128] When the GPS signal is actually broken up, the next sampling period enters a standby condition after the breakup, a sampling signal for one period becomes deficient. Since the 1.5 x Pclk time has elapsed since the previous sampling signal was transmitted, the sampling signal output generated from the internal clock is started by the next timer interrupt.

[00129] Fig. 10 is a drawing illustrating Flowchart 7 of the second embodiment of the present invention.

[001301 Fig. 10 shows a program that causes an external signal interrupt by taking an output of a sampling signal as a trigger when a sampling signal is output in step 502 in Fig. 8 or in step 744 shown in Fig. 9, to thus be executed.

[00131] By the output of the sampling signal, the external signal interrupt is started, and processing starts from step 701. In next step 550, the sampling signal output time is stored in preparation for interruption of the sampling signal, which would be caused by an abnormal in the GPS signal. Processing pertaining to steps subsequent to step 551 is performed for each sampling signal and identical with processing pertaining to steps subsequent to step 551 of Flowchart 2 shown in Fig. 4, and hence its explanation is omitted.

[001321 The processing procedures described thus far by reference to Figs. 8, 9, and apply to operation of the master station 281.

[00133] In addition, like the first embodiment, interrupt processing to be performed when transmission data are received from the master station, which is shown in Flowchart 3 shown in Fig. 5 and Flowchart 4 shown in Fig. 6, is used as it is even in the second embodiment.

[00134] In the second embodiment of the present invention, the digital protective relaying system is operated primarily by use of the GPS signal. Hence, an accurately, synchronous system can be established. Further, the system is operated by reference to the GPS signal since initial installation and start-up of the system. Therefore, there is obviated a necessity for adjusting deviation of a sampling signal between digital protective relays incidental to operation originating from the internal clock, so that the installation and start-up of the relay system become considerably simple.

Third Embodiment [00135] Fig. 11 is a block diagram illustrating a configuration of a third embodiment of the present invention.

[00136] A digital protective relaying system 3 is built by connection of a first digital protective relay 182 and a second digital protective relay 282 that are adjacent to each other.

[00137] The first digital protective relay 182 is called a slave station, and the second protective relay 282 is called a master station; however, they can also be called inversely, as in the first embodiment.

[00138] In relation to functional blocks in the slave station 182 and the master station 282, blocks having the same functions as those described in connection with the first embodiment are assigned the same reference numerals.

[001391 Explanations are given to differences between the present embodiment and the first embodiment by comparison with the first embodiment. In the first embodiment, the sampling signal output unit A 106 has the internal clock and receives the GPS signal 138, makes a correction to the GPS signal, and outputs a sampling signal. As indicated by the flowchart shown in Fig. 4, the sampling signal is produced by a timer interrupt caused by the internal clock.

[00140] In the first embodiment, when the GPS signal has become abnormal, the timing difference calculation unit 110 outputs the timing difference L\T between the sampling signal of the master station and the sampling signal of the slave station to the first correction unit 111. The first correction unit 111 shifts the output timing of the sampling signal 133, thereby achieving synchronization. On the contrary, the third embodiment differs from the first embodiment in the following points. Namely, the timing difference calculation unit 110 transmits data pertaining to the timing difference ai to the master station via the data communication unit 105. A third correction unit 219 of the master station is thereby caused to shift output timing of the sampling output signal of the master station, thereby synchronizing the sampling signal of the master station with the sampling signal of the slave station.

[001411 In the third embodiment of the present invention, the slave station shares operation for calculating the timing difference AT, and the master station shares operation for shifting the sampling signal according to the timing difference AT. As a result, loads on the master station and loads on the slave station can thus be leveled.

Consequently, occurrence of unstable operation, which would otherwise be caused by excessive loads, can be prevented. Moreover, a microcomputer capable of performing high speed processing does not need to be set in only slave stations. All in all, protective relays can be standardized, and hence good economy is achieved.

Fourth Embodiment 100142] Figs. 12 and 13 are views illustrating sampling synchronization processing 2 and 3 of a fourth embodiment of the present invention.

[00143] Figs. 12 and 13 show a method for correcting timing of a sampling signal by use of a synchronation index pulse that is an I-IlL signal whose period is I/n of a period of the sampling signal generated from a received GPS signal when the GPS signal is normal.

[00144] In Fig. 12, (a) shows a synchronization index pulse generated from a received GPS signal. The synchronization index pulse is a signal whose period is 1/n of the period of the sampling signal. Fig. 12 shows a case where n=1 is achieved. A point in time when a signal level changes from L to H; namely, when a signal rises, is correct output timing of the sampling signal.

[00145] (b) shows a dead zone. When the sampling signal is in a dead zone corresponding to a high level, the sampling signal is deemed to be emitted at correct timing by taking the GPS signal as a reference. No correction is made to timing of the sampling signal.

[001461 (c) shows a sampling signal. A position of the arrow denotes output timing of a sampling signal. When a reference is made to the synchronization index pulse (a) at sampling signal output timing on the left, the signal level is L. Hence, the next sampling signal is generated while delayed by a predetermined time. Sampling signal output timing on the right in (c) is illustrated as being delayed by a predetermined amount of correction while the original timing is indicted by a broken line.

[001471 In Fig. 13, (a), (b), and (c) show signals of the same type as that shown in Fig. 12. A reference is made to the synchronization index pulse (a) at the sampling signal output timing on the left in (c), the signal level is high. Hence, the next sampling signal is produced ahead by a predetermined time. Sampling signal output timing on the right in (c) is illustrated as being advanced by a predetermined amount of correction while the original timing is indicted by a broken line.

[00148] As shown in Figs. 12 and 13, the level of the synchronization index pulse is ascertained every time the sampling signal is output. Accordingly, the sampling signal can simply be synchronized with the GPS signal by making a predetermined amount of advancement correction or delay correction.

[00149] Figs. 12 and 13 show a case of n=1. So long as a number of n=2 or more is taken, a plurality of sampling signals can also be synchronized while remaining out of phase with each other by a predetermined amount, by a single synchronization index pulse.

[00150] Synchronization can also be achieved even when the sequence of HIL of the synchronization index pulse is interchanged.

[00151] The configuration of the fourth embodiment of the present invention is the same as that illustrated in the block diagram shown in Fig. I or 11.

[00152] Correcting the sampling signal by the synchronization index pulse shown in Figs. 12 and 13 is performed by the sampling signal output unit A 106 or 206 shown in Fig. I or 11.

[00153] The digital protective relaying system of the fourth embodiment is built by connection of the slave station 101 and the master station 201 shown in Fig. 1 or the slave station 182 and the master station 282 shown in Fig. 11. Explanations are primarily given to operation of the slave station.

[00154] Fig. 14 shows Flowchart 8 of the fourth embodiment of the present invention.

In Fig. 14, processing pertaining to only steps 517 and 518 in Fig. 3 that shows Flowchart 1 of the first embodiment of the present invention is drawn out to be exerted.

[00155] Step 800 shown in Fig. 14 shows start of interrupt processing in which a program starts when an interrupt is caused as a result of receipt of the GPS signal 138 from the GPS receiver.

[00156] When a GF'S signal receipt interrupt has occurred, the GPS signal is determined to be uninterrupted and reliable, so that the GPS signal abnormal timer is cleared in step 517. The GF'S normal counter is incremented in step 518, and interrupt processing ends in step 819.

[00157] Figs. 15 and 16 are drawings illustrating Flowchart 9 and Flowchart 10 of the fourth embodiment of the present invention.

[00158] Fig. 15 provides an explanation about operation of the slave station 101 or 182.

[00159] In Fig. 15, step 542 in Fig. 4 that shows Flowchart 2 of the first embodiment of the present invention is replaced with steps 841 to 855.

1001601 First, a sampling signal is output in step 541.

[00161J Next, a level of the synchronization index pulse is read in step 841. In addition, reading is performed so as to determine whether or not the sampling pulse is in a dead zone.

1001621 When the sampling signal is determined to tall in the dead zone in step 851, processing proceeds to step 551. When the sampling signal is outside the dead zone, a check is made in step 852 as to whether or not the level of the synchronization index pulse is high. When the level is low, processing proceeds to step 853. The timer start-up time for the next time is delayed by a predetermined time, thereby making the sampling signal close to rise timing of the synchronization index pulse originated from the OPS signal. Thus, processing proceeds to step 551. When the level is determined to be high in step 852, processing proceeds to step 855, where the timer start-up time for the next time is advanced by a predetermined time, thereby likewise making the sampling signal close to the rise timing of the synchronization index pulse of the GPS signal. Processing then proceeds to step 551. Processing pertaining to steps 551 to 562 shown in Fig. 15 and processing pertaining to subsequent step 562 shown in Fig. 16 to the end of the interrupt processing are similar to that shown in Fig. 4, and hence their explanations are omitted.

[00163] Fig. 17 is a drawing illustrating Flowchart 11 of the fourth embodiment of the present invention. Fig. 17 provides an explanation about operation of the slave station 101 or 182.

[00164] In Fig. 17, steps 603 to 609 in Fig. 5 that shows Flowchart 3 of the first embodiment of the present invention are replaced with step 805.

[001651 In step 805, a determination is made along with results of determination made in steps 610 and 611 only when the GPS signal abnormal timer provides a value that is smaller than the predetermined value Ti, and there may be a case where the value a will be updated in steps 612 to 614. When in step 805 the GPS signal abnormal timer shows a value that is the predetermined value Ti or more, processing proceeds to step 621, and the value a is not updated.

[00166] The other steps are the same as those shown in Figs. 5 and 6, and hence their explanations are omitted.

[00167] In the fourth embodiment of the present invention, a check is made to the level of the synchronization index pulse that is the H/L signal whose period is i/n of the period of the sampling signal produced from the GPS signal, whereby the sampling signal can be synchronized with the GPS signal.

[00168] There is no necessity for calculating a difference between the period of the GPS signal and the period of the sampling signal and a correction value from the difference. Synchronizing the sampling signal to the GPS signal can be accomplished by only simple control including checking the level of the synchronization index pulse generated at the time of output of the sampling signal, to thus effect advanced or delayed control.

[001691 Therefore, enhancement of reliability, cost reduction, shortening of a calculation time, and lessening of a calculation load can be expected.

[00179] Any of the first through fourth embodiments may also be combined together.

[00171] The first through fourth embodiments have provided the explanations about the sampling synchronization method for the digital protective relaying system.

Namely, the protective relay optimizes timing of the sampling signal by use of the signal from the OPS receiver. The delay time difference a is calculated from the third data communication delay time Tsm between output of the sampling signal and receipt of data from an adjacent protective relay and the fourth data communication delay time Tsm between output of the sampling signal from the adjacent protective relay and receipt of the data. The thus-calculated delay time difference a is stored. When the GPS signal has become abnormal, the sampling signal from the adjacent protective relay is synchronized by newly-determined Tms and Tsm and the stored value a.

[00172] So long as the synchronization method is used, when the signal from the GPS receiver has become abnormal, it is possible to correct the sampling signal by a simple method without involvement of a great change in the calculation method.

Further, even when a data communication delay time that occurs during exchange of data between adjacent protective relays changes from outgoing communication to incoming communication, the sampling signal can be accurately corrected.

[00173] The present invention can be implemented in illustrative non-limiting aspects as follows: 100174] (1) According to a first aspect, there is provided a digital protective relaying system equipped with first and second digital protective relays that are connected to each other via a power transmission line and that respectively sample an electrical quantity of an electric power system while synchronized together based on a GPS signal, wherein the first digital protective relay comprises: a first sampling signal output unit that outputs a first sampling signal used for determining timing for sampling the electrical quantity at a predetermined period; a data communication unit that transmits first electrical quantity data sampled based on the first sampling signal to the second digital protective relay via a first data communication path and that receives second electrical quantity data which have been sampled based on a second sampling signal output from a second sampling signal output unit of the second digital protective relay and which have been transmitted via a second data communication path; a delay time difference calculation unit that calculates a delay time difference between a second data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data and a first data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the first data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit; a storage unit for storing the delay time difference; a timing difference calculation unit that calculates a timing difference between the first sampling signal and the second sampling signal when the OPS signal is abnormal, from a fourth data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data, a third data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the third data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit, and the delay time difference which have been acquired while the OPS signal is normal and which is read from the storage unit; and a first correction unit that corrects the first sampling signal according to the timing difference, thereby synchronizing the first sampling signal to the second sampling signal.

100175] (2) According to a second aspect, there is provided the digital protective relaying system according to the first aspect, wherein the delay time difference calculation unit calculates a delay time difference cc, from a second data communication delay time Tdl between the output of the first sampling signal and the receipt of the second electrical quantity data and a first data communication delay time 1d2 between the output of the second sampling signal and the receipt of the first electrical quantity data, by an equation of a = Td2 -IdI; and the timing difference calculation unit calculates a timing difference AT between the first sampling signal and the second sampling signal, when the GPS signal is abnormal, from a third data communication delay time Tsm, a fourth data communication delay time Tms, and the delay time difference a which have been acquired when the GPS signal ié normal and which is read from the storage unit, by an equation of AT = (Tms -Tsm + cc)12.

[00176] (3) According to a third aspect, there is provided a digital protective relaying system equipped with first and second digital protective relays that are connected to each other via a power transmission line and that respectively sample an electrical quantity of an electric power system while synchronized together, wherein the first digital protective relay comprises: a first sampling signal output unit that outputs a first sampling signal used for determining timing for sampling the electrical quantity at a predetermined period; a data communication unit that transmits first electrical quantity data sampled based on the first sampling signal to the second digital protective relay via a first data communication path and that receives second electrical quantity data which have been sampled based on a second sampling signal output from a second sampling signal output unit of the second digital protective relay and which have been transmitted via a second data communication path; a delay time difference calculation unit that calculates a delay time difference between a second data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data and a first data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the first data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit; a storage unit for storing the delay time difference; a reference signal generation unit that generates a reference signal upon receipt of a GPS signal; a backup reference signal generation unit that includes a internal clock and generates a backup reference signal based on a signal of the internal clock; a second correction unit that corrects the backup reference signal based on the reference signal; a switching unit that inputs the reference signal to the sampling signal output unit when the GPS signal is normal, and that inputs a signal, which is generated by correcting the backup reference signal by the second correction unit, in place of the reference signal when the GPS signal is abnormal; a timing difference calculation unit that calculates a timing difference between the first sampling signal and the second sampling signal when the GPS signal is abnormal, from a fourth data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data, a third data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the third data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit, and the delay time difference which has been acquired while the GPS signal is normal and which is read from the storage unit; and a first correction unit that corrects the first sampling signal according to the timing difference, thereby synchronizing the first sampling signal to the second sampling signal.

100177] (4) According to a fourth aspect, there is provided the digital protective relaying system according to the third aspect, wherein the delay time difference calculation unit calculates a delay time difference a, from a second data communication delay time Tdl between the output of the first sampling signal and the receipt of the second electrical quantity data and a first data communication delay time Td2 between the output of the second sampling signal and the receipt of the first electrical quantity data, by an equation of a = Td2 -Tdl; and the timing difference calculation unit calculates a timing difference aT between the first sampling signal and the second sampling signal, when the GPS signal is abnormal, from a third data communication delay time Tsm, a fourth data communication delay time Ims, and the delay time difference a which have been acquired when the GPS signal is normal and which are read from the storage unit, by an equation of 4\T = (Ims -Tsm + a)/2.

[00178] (5) According to a fifth aspect, there is provided a digital protective relaying system equipped with first and second digital protective relays that are connected to each other via a power transmission line and that respectively sample an electrical quantity of an electric power system while synchronized together based on a GE'S signal, wherein the first digital protective relay comprises: a first sampling signal output unit that outputs a first sampling signal used for determining timing for sampling the electrical quantity at a predetermined period; a data communication unit that transmits first electrical quantity data sampled based on the first sampling signal to the second digital protective relay via a first data communication path and that receives second electrical quantity data which have been sampled based on a second sampling signal output from a second sampling signal output unit of the second digital protective relay and which have been transmitted via a second data communication path; a delay time difference calculation unit that calculates a delay time difference between a second data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data and a first data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the first data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit; a storage unit for storing the delay time difference; and a timing difference calculation unit that calculates and outputs a timing difference between the first sampling signal and the second sampling signal when the GPS signal is abnormal, from a fourth data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data, a third data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the third data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit, and the delay time difference which has been acquired while the GPS signal is normal and which is read from the storage unit, and wherein the second digital protective relay has a third correction unit that synchronizes the first sampling signal with the second sampling signal by correcting the second sampling signal according to the timing difference received from the first protective relay via the data communication unit.

[00179J (6) According to a sixth aspect, there is provided the digital protective relaying system according to any one of the firth to fifth aspects, wherein the delay time difference calculation unit calculates the delay time difference between the first data communication delay time and the second data communication delay time when the GPS signal is abnormal.

[00180J (7) According to a seventh aspect, there is provided the digital protective relaying system according to the sixth aspect, wherein, when the GPS signal is abnormal and when a change has occurred in at least one of the first data communication path and the second data communication path between the first and second digital protective relays, the delay time difference calculation unit calculates the delay time difference between the first data communication delay time and the second data communication delay time.

[00181] (8) According to an eighth aspect, there is provided the digital protective relaying system according to the sixth aspect, wherein the delay time difference calculation unit calculates the delay time difference between the first data communication delay time and the second data communication delay time for a predetermined period after the GPS signal has become abnormal, and the delay time difference is stored in the storage unit.

[00182] (9) According to a ninth aspect, there is provided the digital protective relaying system according to the third aspect, wherein, when an amount of correction of the second correction unit that makes a correction by comparison of a backup reference signal with a reference signal when the GPS signal is normal is a predetermined value or less, the delay time difference calculation unit calculates the delay time difference from the first data communication delay time and the second data communication delay time for a predetermined period after the GPS signal has become abnormal, and the storage unit stores the delay time difference.

1001831 (10) According to a tenth aspect, there is provided the digital protective relaying system according to the ninth aspect, wherein the predetermined period is determined according to the amount of correction of the second correction unit that makes a correction by comparison of the backup reference signal with the reference signal when the GPS signal is normal.

[00184J (11) According to an eleventh aspect, there is provided the digital protective relaying system according to the tenth aspect, wherein the amount of correction of the second correction unit that makes a correction by comparison of the backup reference signal with the reference signal when the GPS signal is normal is divided into a fixed correction value and a variable correction value, the fixed correction value and the variable correction value are stored, and the predetermined period is determined according to the variable correction value.

1001851 (12) According to a twelfth aspect, there is provided the digital protective relaying system according to any one of the first, second, fifth, sixth, seventh and eighth aspect, further comprising: a first synchronization index pulse generation unit that outputs a first synchronization index pulse corresponding to the first sampling signal and a second synchronization index pulse generation unit that outputs a second synchronization index pulse corresponding to the second sampling signal, wherein the first and second synchronization index pulses have a period that is 1/n of a period of the first and second sampling signals and are produced from the GPS signal, and the first and second sampling signal output units corrects a subsequent sampling timing by a predetermined amount according to a level of the first and second synchronization index pulses acquired when the first and second sampling signals are output.

1001861 (13) According to a thirteenth aspect, there is provided a sampling synchronization method for a digital protective relaying system equipped with first and second digital protective relays that are connected to each other via power transmission lines and that respectively sample an electrical quantity while synchronized together based on a OPS signal, the method comprising: sampling first electrical quantity data by the first digital protective relay at a predetermined period based on a first sampling signal and transmitting the data to the second digital protective relay via a first data communication path; sampling second electrical quantity data by the second digital protective relay at a predetermined period based on a second sampling signal and transmitting the data to the first digital protective relay via a second data communication path; synchronizing the first sampling signal to the second sampling signal based on the GPS signal; measuring a second communication delay time between output of the first sampling signal and receipt of the second electrical quantity data; measuring a first communication delay time between output of the second sampling signal and receipt of the first electrical quantity data; calculating a communication delay time difference between the first communication delay time and the second communication delay time and storing the communication delay time difference in storage unit; measuring a fourth communication delay time between output of the first sampling signal and receipt of the second electrical quantity data when the GPS signal is abnormal; measuring a third communication delay time between output of the second sampling signal and receipt of the first electrical quantity data when the GPS signal is abnormal; calculating an amount of deviation between the first sampling signal and the second sampling signal from the third communication delay time, the fourth communication delay time and the communication delay time difference that is read from the storage unit and that has been acquired when the GPS signal is normal, and correcting the first sampling signal, thereby synchronizing the first sampling signal to the second sampling signal.

Claims

CLAI MS1. A digital protective relaying system equipped with first and second digital protective relays that are connected to each other via a power transmission line and that respectively sample an electrical quantity of an electric power system while synchronized together based on a GPS signal, wherein the first digital protective relay comprises: a first sampling signal output unit that outputs a first sampling signal used for determining timing for sampling the electrical quantity at a predetermined period; a data communication unit that transmits first electrical quantity data sampled based on the first sampling signal to the second digital protective relay via a first data communication path and that receives second electrical quantity data which have been sampled based on a second sampling signal output from a second sampling signal output unit of the second digital protective relay and which have been transmitted via a second data communication path; a delay time difference calculation unit that calculates a delay time difference between a second data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data and a first data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the first data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit; a storage unit for storing the delay time difference; a timing difference calculation unit that calculates a timing difference between the first sampling signal and the second sampling signal when the GPS signaJ is abnormal, from a fourth data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data, a third data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the third data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit, and the delay time difference which have been acquired while the GPS signal is normal and which is read from the storage unit; and a first correction unit that corrects the first sampling signal according to the timing difference, thereby synchronizing the first sampling signal to the second sampling signal.
2. A digital protective relaying system according to claim 1, wherein the delay time difference calculation unit calculates a delay time difference a, from a second data communication delay time Tdl between the output of the first sampling signal and the receipt of the second electrical quantity data and a first data communication delay time Td2 between the output of the second sampling signal and the receipt of the first electrical quantity data, by an equation of ctzTd2_Tdl; and the timing difference calculation unit calculates a timing difference AT between the first sampling signal and the second sampling signal, when the GPS signal is abnormal, from a third data communication delay time Tsm, a fourth data communication delay time Tms, and the delay time difference a which have been acquired when the GPS signal is normal and which is read from the storage unit, by an equation of AT=(Tms-Tsm+a)/2.
3. A digital protective relaying system equipped with first and second digital protective relays that are connected to each other via a power transmission line and that respectively sample an electrical quantity of an electric power system while synchronized together, wherein the first digital protective relay comprises: a first sampling signal output unit that outputs a first sampling signal used for determining timing for sampling the electrical quantity at a predetermined period: a data communication unit that transmits first electrical quantity data sampled based on the first sampling signal to the second digital protective relay via a first data communication path and that receives second electrical quantity data which have been sampled based on a second sampling signal output from a second sampling signal output unit of the second digital protective relay and which have been transmitted via a second data communication path; a delay time difference calculation unit that calculates a delay time difference between a second data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data and a first data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the first data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit; a storage unit for storing the delay time difference; a reference signal generation unit that generates a reference signal upon receipt of a GPS signal; a backup reference signal generation unit that includes a internal clock and generates a backup reference signal based on a signal of the internal clock; a second correction unit that corrects the backup reference signal based on the reference signal; a switching unit that inputs the reference signal to the sampling signal output unit when the GPS signal is normal, and that inputs a signal, which is generated by correcting the backup reference signal by the second correction unit, in place of the reference signal when the GPS signal is abnormal; a timing difference calculation unit that calculates a timing difference between the first sampling signal and the second sampling signal when the OPS signal is abnormal, from a fourth data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data, a third data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the third data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit, and the delay time difference which has been acquired while the GPS signal is normal and which is read from the storage unit; and a first correction unit that corrects the first sampling signal according to the timing difference, thereby synchronizing the first sampling signal to the second sampling signal.
4. A digital protective relaying system according to claim 3, wherein the delay time difference calculation unit calculates a delay time difference a, from a second data communication delay time Idi between the output of the first sampling signal and the receipt of the second electrical quantity data and a first data communication delay time Td2 between the output of the second sampling signal and the receipt of the first electrical quantity data, by an equation of cxTd2-Tdl; and the timing difference calculation unit calculates a timing difference AT between the first sampling signal and the second sampling signal, when the GPS signal is abnormal, from a third data communication delay time Tsm, a fourth data communication delay time Tms, and the delay time difference a which have been acquired when the GPS signal is normal and which are read from the storage unit, by an equation of AT = (Tms -Tsm + a)/2.
5. A digital protective relaying system equipped with first and second digital protective relays that are connected to each other via a power transmission line and that respectively sample an electrical quantity of an electric power system while synchronized together based on a GPS signal, wherein the first digital protective relay comprises: a first sampling signal output unit that outputs a first sampling signal used for determining timing for sampling the electrical quantity at a predetermined period; a data communication unit that transmits first electrical quantity data sampled based on the first sampling signal to the second digital protective relay via a first data communication path and that receives second electrical quantity data which have been sampled based on a second sampling signal output from a second sampling signal output unit of the second digital protective relay and which have been transmitted via a second data communication path; a delay time difference calculation unit that calculates a delay time difference between a second data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data and a first data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the first data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit; a storage unit for storing the delay time difference; and a timing difference calculation unit that calculates and outputs a timing difference between the first sampling signal and the second sampling signal when the GPS signal is abnormal, from a fourth data communication delay time between output of the first sampling signal and receipt of the second electrical quantity data, a third data communication delay time between output of the second sampling signal and receipt of the first electrical quantity data, the third data communication delay time being calculated and transmitted by the second digital protective relay and being received via the data communication unit, and the delay time difference which has been acquired while the GPS signal is normal and which is read from the storage unit, and wherein the second digital protective relay has a third correction unit that synchronizes the first sampling signal with the second sampling signal by correcting the second sampling signal according to the timing difference received from the first protective relay via the data communication unit.
6. A digital protective relaying system according to any one of claims 1 to 5, wherein the delay time difference calculation unit calculates the delay time difference between the first data communication delay time and the second data communication delay time when the GPS signal is abnormal.
7. A digital protective relaying system according to claim 6, wherein, when the GPS signal is abnormal and when a change has occurred in at least one of the first data communication path and the second data communication path between the first and second digital protective relays, the delay time difference calculation unit calculates the delay time difference between the first data communication delay time and the second data communication delay time.
8. A digital protective relaying system according to claim 6, wherein the delay time difference calculation unit calculates the delay time difference between the first data communication delay time and the second data communication delay time for a predetermined period after the GPS signal has become abnormal, and the delay time difference is stored in the storage unit.
9. A digital protective relaying system according to claim 3, wherein, when an amount of correction of the second correction unit that makes a correction by comparison of a backup reference signal with a reference signal when the GPS signal is normal is a predetermined value or less, the delay time difference calculation unit calculates the delay time difference from the first data communication delay time and the second data communication delay time for a predetermined period after the GPS signal has become abnormal, and the storage unit stores the delay time difference.
10. A digital protective relaying system according to claim 9, wherein the predetermined period is determined according to the amount of correction of the second correction unit that makes a correction by comparison of the backup reference signal with the reference signal when the GPS signal is normal.
11 A digital protective relaying system according to claim 10, wherein the amount of correction of the second correction unit that makes a correction by comparison of the backup reference signal with the reference signal when the GPS signal is normal is divided into a fixed correction value and a variable correction value, the fixed correction value and the variable correction value are stored, and the predetermined period is determined according to the variable correction value.
12. A digital protective relaying system according to any one of claims 1, 2, 5, 6, 7, and 8, further comprising: a first synchronization index pulse generation unit that outputs a first synchronization index pulse corresponding to the first sampling signal and a second synchronization index pulse generation unit that outputs a second synchronization index pulse corresponding to the second sampling signal, wherein the first and second synchronization index pulses have a period that is 1/n of a period of the first and second sampling signals and are produced from the GPS signal, and the first and second sampling signal output units corrects a subsequent sampling timing by a predetermined amount according to a level of the first and second synchronization index pulses acquired when the first and second sampling signals are output.
13. A sampling synchronization method for a digital protective relaying system equipped with first and second digital protective relays that are connected to each other via power transmission lines and that respectively sample an electrical quantity while synchronized together based on a GPS signal, the method comprising: sampling first electrical quantity data by the first digital protective relay at a predetermined period based on a first sampling signal and transmitting the data to the second digital protective relay via a first data communication path; sampling second electrical quantity data by the second digital protective relay at a predetermined period based on a second sampling signal and transmitting the data to the first digital protective relay via a second data communication path; synchronizing the first sampling signal to the second sampling signal based on the GPS signal; measuring a second communication delay time between output of the first sampling signal and receipt of the second electrical quantity data; measuring a first communication delay time between output of the second sampling signal and receipt of the first electrical quantity data; calculating a communication delay time difference between the first communication delay time and the second communication delay time and storing the communication delay time difference in storage unit; measuring a fourth communication delay time between output of the first sampling signal and receipt of the second electrical quantity data when the GPS signal is abnormal; measuring a third communication delay time between output of the second sampling signal and receipt of the first electrical quantity data when the GPS signal is abnormal; calculating an amount of deviation between the first sampling signal and the second sampling signal from the third communication delay time, the fourth communication delay time and the communication delay time difference that is read from the storage unit and that has been acquired when the GPS signal is normal, and correcting the first sampling signal, thereby synchronizing the first sampling signal to the second sampling signal.