Control system method of protectively controlling electric power system and storage medium storing program code

• US 6,618,648 B1
• Filed: 03/04/1999
• Issued: 09/09/2003
• Est. Priority Date: 03/05/1998
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Hori, Masao, Miyoshi, Tetsuya, Shimokawa, Yoshiyuki, Fuwa, Yutaka, Sasaki, Hideki, Sekiguchi, Katsuhiko, Shirota, Yoshihiro
• Primary Examiner(s): Picard, Leo
• Assistant Examiner(s): Rao, Sheela S.
• Application Number:
  US09/262,288
• Time in Patent Office: 1,650 Days
• Field of Search: 700/286, 700/291, 700/292, 700/299
• US Class Current: 700/291
• CPC Class Codes: G01R 31/088 Aspects of digital computing
• CPC Class Codes: G01R 31/3271 of high voltage or medium voltage devices G01R31/333 takes precedence
• CPC Class Codes: H02H 7/262 involving transmissions of switching or blocking orders
• CPC Class Codes: H02H 7/263 involving transmissions of measured values comparison of currents or voltages using pilot wires H02H3/30
• CPC Class Codes: H02H 7/28 for meshed systems
• CPC Class Codes: H02J 13/00001 characterised by the display of information or by user interaction, e.g. supervisory control and data acquisition systems [SCADA] or graphical user interfaces [GUI]
• CPC Class Codes: H02J 13/00006 characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
• CPC Class Codes: H02J 13/00017 using optical fiber
• CPC Class Codes: H02J 13/00034 the elements or equipment being or involving an electric power substation
• CPC Class Codes: H02J 13/0004 involved in a protection system
• CPC Class Codes: H02J 3/00 Circuit arrangements for ac mains or ac distribution networks
• CPC Class Codes: H02J 3/0012 Contingency detection
• CPC Class Codes: Y02B 90/20 Smart grids as enabling technology in buildings sector smart grids supporting the management or operation of end-user stationary applications in general, or like technologies with no associated climate change mitigation effect Y04S20/00
• CPC Class Codes: Y02E 60/00 Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier
• CPC Class Codes: Y04S 10/20 using protection elements, arrangements or systems
• CPC Class Codes: Y04S 10/40 Display of information, e.g. of data or controls
• CPC Class Codes: Y04S 20/00 Management or operation of end-user stationary applications or the last stages of power distribution; Controlling, monitoring or operating thereof
• CPC Class Codes: Y04S 40/12 characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment
• CPC Class Codes: Y04S 40/124 using wired telecommunication networks or data transmission busses

Abstract

The control system for a plant comprises a rectifier connected to a network. The rectifier has a unit for acquiring precise time, a unit for sampling the state quantity on the precise time to convert the state quantity into digital data and a unit for adding the precise time at each sampling timing to the digital data to transmit the digital data each having the precise time to the network. A breaker is connected to the network. The breaker has a unit for receiving, through the network, a control command thereto and a unit for transmitting an operating state thereof to the network. A control apparatus is connected to the network. The control apparatus has a unit for performing an operation process on the digital data transmitted through the communication network and the operating state of the breaker transmitted therethrough and a unit for transmitting the control command through the communication network to the breaker in response to a result of the control operation process of the performing unit.

Claims

1. A control system for controlling a plant according to a state quantity related to the plant and inputted therefrom, said system comprising:

a communication network;

an input device connected to the communication network so that data communication is permitted, said input device having;

means for acquiring a precise time,

inputting means for inputting the state quantity related to the plant therefrom,

converting means for sampling the inputted state quantity according to the acquired precise time so as to convert the state quantity into digital data and

first transmitting means for adding the precise time at each sampling timing to the digital data so as to transmit the digital data each having the precise time to the communication network;

an opening/closing device connected to the communication network so that data communication is permitted and adapted to opening and closing a part of the plant,

said opening/closing device having;

means for receiving, through the communication network, a control command with respect to the opening/closing device and

second transmitting means for transmitting an operating state of the opening/closing device to the communication network; and

a control apparatus connected to the communication network so that data communication is permitted, said control apparatus having;

means for performing a control operation process according to the digital data transmitted through the communication network and the operating state of the opening/closing device transmitted therethrough and

third transmitting means for transmitting the control command through the communication network to the opening/closing device in response to a result of the control operation process of the performing means, wherein

 

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

2. An electric power system protective control system for controlling an electric power system according to a state quantity related to the electric power system and inputted therefrom, said protective control system comprising:

a communication network;

an input device connected to the communication network so that data communication is permitted, said input device having;

means for acquiring a precise time,

inputting means for inputting the state quantity related to the electric power system therefrom,

converting means for sampling the inputted state quantity according to the acquired precise time so as to convert the state quantity into digital data and

first transmitting means for adding the precise time at each sampling timing to the digital data so as to transmit the digital data each having the precise time to the communication network;

an opening/closing device connected to the communication network so that data communication is permitted and adapted to opening and closing a part of the electric power system,

said opening/closing device having;

means for receiving, through the communication network, a control command with respect to the opening/closing device and

second transmitting means for transmitting an operating state of the opening/closing device to the communication network; and

a protective control apparatus connected to the communication network so that data communication is permitted, said control apparatus having;

means for performing a protective control operation process according to the digital data transmitted through the communication network and the operating state of the opening/closing device transmitted therethrough and

third transmitting means for transmitting the control command through the communication network to the opening/closing device in response to a result of the protective control operation process of the performing means, wherein

 

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

3. An electric power system protective control system according to claim 2, wherein said input device is provided with means for self-diagnosing an operating state thereof so as to transmit a result of the self-diagnosis to the communication network, and said opening/closing device is provided with means for receiving the result of the self-diagnosis through the communication network so as to control an opening/closing operation of the opening/closing device according to the received result of the self-diagnosis.

4. An electric power system protective control system according to claim 2, wherein said input device is composed of a plurality of input devices,

said converting means of each of the input devices is adapted to sample the state quantity at predetermined periods in accordance with the precise time acquired by the acquiring means while synchronizing the state quantities of the respective input devices with each other, and to convert the sampled state quantities into digital data,

said first transmitting means of each of the input devices is adapted to add the precise time at each sampling timing to each converted digital data and to transmit the digital data each having the precise time to the communication network, and

wherein said control process performing means has means for receiving the digital data each having the precise time of each of the input devices and the operating state of the opening/closing device through the communication network, means for time-sequentially arranging the received digital data in accordance with the precise time of each received digital data for each of the input devices and means for performing the protective control operation process in accordance with the time-sequentially arranged digital data by the arranging means.

5. An electric power system protective control system according to claim 4, wherein said acquiring means, said converting means and said first transmitting means are constituted by a computer circuit having hardware elements including a CPU and a memory unit, said computer circuit being provided with means for self-diagnosing an operating state of the computer circuit and means for transmitting a result of the self-diagnosis performed by the self-diagnosing means to the communication network,

and wherein said opening/closing device is provided with means for receiving the result of the self-diagnosis transmitted through the communication network and means for locking control of the operation of the opening/closing device in response to the result of the self-diagnosis received by the result receiving means.

6. An electric power system protective control system according to claim 2, wherein said input device and said opening/closing device are provided for plurality of electric stations, respectively, said electric stations being distributed, said acquiring means, said converting means and said first transmitting means are provided for the respective input devices of the respective electric stations, said control command receiving means and said second transmitting means are provided for the respective opening/closing devices of the respective electric stations, said control operation performing means and said third transmitting means are provided for at least one of the dispersively disposed electric stations, said communication network is composed of a first communication network in a local area constituted in each of the electric stations and a second communication network for widely connecting the dispersively disposed electric stations to each other,

said converting means of each of the input devices in the electric station is adapted to sample the state quantity of its own input device at predetermined periods in accordance with the precise time acquired by the acquiring means while synchronizing the state quantities of the respective input devices with each other, and to convert the sampled state quantities into digital data,

said first transmitting means of each of the input devices is adapted to add the precise time at each sampling time to each converted digital data and to transmit the digital data each having the precise time through the first communication network to the second communication network, and

wherein said control operation performing means of the at least one of the electric stations has means for receiving the digital data each having the precise time of each of the input devices and the operating state of the opening/closing device transmitted through the first and second communication networks, means for time-sequentially arranging the received digital data in accordance with the precise time of each received digital data for each of the input devices and means for performing the protective control operation process in accordance with the time-sequentially arranged digital data by the arranging means.

7. An electric power system protective control system for performing an operation process in accordance with a state quantity inputted from an electric power system so as to protectively control the electric power system, said protective control system comprising:

a communication network;

a digital protective control apparatus connected to the communication network so that data communication is permitted, said digital protective control apparatus comprising;

means for acquiring a precise time, converting means for sampling the state quantity inputted from the electric power system according to the acquired precise time so as to convert the state quantity into digital data and

transmitting means for adding the precise time to the converted digital data at each sampling timing so as to transmit the digital data each having the precise time to the communication network;

means for receiving the digital data transmitted through the communication network, each of said digital data having the precise time and

means for time-sequentially arranging the received digital data each having the precise time in accordance with the precise time of each of the received digital data, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

8. An electric power system protective control system according to claim 7, wherein said electric power system has a plurality of equipment devices, said digital protective control apparatus is composed of a plurality of digital protective control apparatuses which are provided in correspondence with the equipment devices, respectively,

each of said converting means of each of the digital protective control apparatuses is adapted to sample the state quantity of the corresponding equipment device at predetermined periods in accordance with the precise time acquired by the acquiring means while synchronizing the state quantities of the respective digital protective control apparatuses with each other, and to convert the sampled state quantities into digital data,

each of said transmitting means of each of the digital protective control apparatuses is adapted to add the precise time at each sampling timing to each converted digital data and to transmit the digital data each having the precise time to the communication network,

said receiving means is adapted to receive the digital data each having the precise time of each of the digital protective control apparatuses transmitted through the communication network and

wherein said arranging means is adapted to time-sequentially arrange the received digital data in accordance with the precise time of each received digital data for each of the digital protective control apparatuses.

9. An electric power system protective control system according to claim 8, further comprising display means for displaying a digital data group time-sequentially arranged by the arranging means.

10. An electric power system protective control system according to claim 8, further comprising means for generating a state quantity of a test for a digital protective control apparatus to be tested in accordance with the digital data group time-sequentially arranged by the arranging means.

11. An electric power system protective control system comprising:

a plurality of digital protective control apparatuses for protectively controlling an electric power system;

a communication network for connecting the digital protective control apparatuses to each other so that data communication is permitted, each of said digital protective control apparatuses having;

means for acquiring a precise time,

converting means for sampling a state quantity related to a first equipment device of the electric power system at predetermined periods in accordance with the precise time acquired by the acquiring means so as to convert the sampled state quantities into digital data, said first equipment device being an object for protectively control of the corresponding digital protective control apparatus,

first judgement means for judging whether or not the first equipment device is faulty based on the converted digital data so as to perform a protective control operation process according to a result of the judgement of the first judgement means,

second judgement means for judging whether or not the first equipment device and a second equipment device of the electric power system are faulty based on the converted digital data, said second equipment device being not object for protective control of the corresponding digital protective control apparatus;

recording means for, when the judgement of the second judgement means is made that at least one of the first and second equipment devices is fault, adding the precise time to the converted digital data at each sampling timing so as to record the digital data each having the sampled precise time, and

means for transmitting the digital data recorded by the record means to the communication network, said transmitted digital data having the sampled precise time;

receiving means connected to the communication network for receiving the digital data transmitted through the communication network from each of the digital protective control apparatuses, each of said received digital data having the precise time; and

arranging means for time-sequentially arranging the received digital data according to the sampled precise time thereof for each of the digital protective control apparatuses, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

12. An electric power system protective control system according to claim 11, further comprising display means for displaying a digital data group time-sequentially arranged by the arranging means.

13. An electric power system protective control system according to claim 11, further comprising means for generating a state quantity of a test for a digital protective control apparatus to be tested in accordance with the digital data group time-sequentially arranged by the arranging means.

14. An electric power system protective control system comprising:

a plurality of digital protective control apparatuses for protectively controlling an electric power system; and

a communication network for connecting the digital protective control apparatuses to each other so that data communication is permitted, each of said digital protective control apparatuses having;

means for acquiring a precise time;

converting means for sampling a state quantity related to an equipment device of the electric power system at predetermined periods in accordance with the precise time acquired by the acquiring means so as to convert the sampled state quantities into first digital data, said equipment device being an object for protective control of the corresponding digital protective control apparatus;

transmitting means for adding the precise time at each sampling timing to each first converted digital data so as to transmit the first digital data each having the precise time to the communication network;

means for receiving second digital data having the precise time transmitted from the transmitting means of at least one of other digital protective control apparatuses through the communication network;

arranging means for time-sequentially arranging the received second digital data in accordance with the precise time of each second received digital data; and

means for performing a protective control operation process by using one of the first digital data converted by the converting means and the second digital data time-sequentially arranged by the arranging means, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

15. A control system comprising:

a plurality of control apparatuses adapted to perform an operation process according to a state quantity related to a plant so as to control the plant, said control apparatuses being dispersively arranged; and

a communication network by which the control apparatuses are connected to each other so that data communication is permitted, each of said control apparatuses comprising;

means for acquiring signals at substantially constant periods;

means for sequentially sampling a state quantity related to the plant at a same timing as a timing of other control apparatuses in accordance with the periodic signals acquired by the acquiring means so as to collect digital data; and

means for adding time at each sampling timing based on the periodic signals to the collected digital data so as to sequentially store the digital data each having the time, wherein

said periodic signals have an accuracy of substantially 1 μ

s to 100 ns.

16. An electric power system protective control system comprising:

a plurality of protective control apparatuses adapted to perform a protective control operation process according to a state quantity related to an electric control system for protectively controlling the electric power system, respectively, said control apparatuses being distributed; and

a communication network by which the protective control apparatuses are connected to each other so that data communication is permitted, each of said protective control apparatuses comprising;

means for acquiring signals at substantially constant periods;

collecting means for sequentially sampling the state quantity related to the electric power system at a same timing as a timing of another protective control apparatus in accordance with the periodic signals acquired by the acquiring means so as to collect digital data; and

storage means for adding time at each sampling timing based on the periodic signals to the collected digital data so as to sequentially store the digital data each having the time, wherein

said periodic signals have an accuracy of substantially 1 μ

s to 100 ns.

17. An electric power system protective control system according to claim 16, wherein said acquiring means is composed of means for acquiring precise time and the time at each sampling timing is precise time at each sampling timing.

18. An electric power system protective control system according to claim 17, further comprising a monitor/control unit connected to the communication network and adapted to remotely monitor and control an operation state of the protective control apparatuses, wherein each of said protective control apparatuses is provided with means for performing a protective control operation process based on the digital data so as to determine whether or not abnormal data is detected and means for, when the abnormal data is detected as a result of the protective control operation process, transmitting an abnormal data generation information including detection time to the display/operation unit, said abnormal-data being detected at the detection time,

and wherein said monitor/control unit is provided with means for transmitting, when the abnormal data generation information including the detection time is transmitted from a predetermined protective control apparatus in the protective control apparatuses, a first program module for collecting digital data before and after the detection time to the protective control apparatuses through the communication network along a predetermined route, said first program module previously being provided in the monitor/control unit;

each of said protective control apparatuses being provided with means for receiving the first program module transmitted through the communication network so as to execute the first program module and means for transmitting the digital data having the precise time before and after the detection time to the monitor/control unit in accordance with the first executed program module,

said monitor/control unit being provided with means for locating a fault point related to the abnormal data according to the digital data, said digital data having the precise time before and after the detection time and being transmitted from each of the protective control apparatuses.

19. An electric power system protective control system according to claim 17, wherein each of said protective control apparatuses is provided with:

means for reading out predetermined precise time of precise time stored in the storing means of its own protective control apparatus together with the digital data in accordance with a second program module for measuring a power-transmission line constant, said second program module previously being provided in the monitor/control unit and being transmitted through the communication network therefrom,

means for measuring the power-line transmission constant by using the digital data of the own protective control apparatus and digital data of at least one of other another protective control apparatuses, said digital data of the own-protective control apparatus being added to the predetermined precise time,

means for storing the measured power-transmission line constant and

means for calculating a ranging impedance related to an object for the protective control of the own protective control apparatus on the basis of the measured power-transmission line constant.

20. An electric power system protective control apparatus according to claim 18, wherein said storage means is adapted to store the digital data having the precise time in a period of time from the transmission of the abnormal-data generation information to the monitor/control unit till the transmission of the digital data having the precise time before and after the detection time to the monitor/control unit.

21. An electric power system protective control system according to claim 17, further comprising a monitor/control unit connected to the communication network and adapted to remotely monitor and control an operation state of the protective control apparatuses, wherein each of said protective control apparatuses is provided with means for calculating power-flow information related to the electric power system in accordance with the digital data having the precise time and stored in the storage means, said power-flow information including electric power, ineffective electric power and electric currents, said power-flow information calculating means adding time at which the digital data are collected to the calculated power-flow information so as to transmit the power-flow information to the monitor/control unit through the communication network, said power-flow information being produced on the collected digital data, and

wherein said monitor/control unit is provided with means for determining a stable state of the electric power system according to the power-flow information transmitted from each of the protective control apparatuses through the communication network.

22. An electric power system protective control system according to claim 18, wherein said storage means, said control operation process performing means, said abnormal data information transmitting means, said first program module executing means and said digital data transmitting means are constituted by a computer circuit having hardware elements including a first CPU, a second CPU, a memory unit commonly provided for the first and second CPU and a communication interface commonly provided for the first and second CPU,

said first CPU is adapted to use the common memory unit so as to perform the process related to the storage means and the process related to the protective control operation process performing means, respectively, and

wherein said second CPU is adapted to use the common memory unit and the common communication interface so as to perform the process related to the abnormal data information transmitting means, the process related to the program module executing means and the process related to the digital data transmitting means, respectively.

23. An electric power system protective control system according to claim 18, wherein said storage means, said control operation process performing means, said abnormal data information transmitting means, said first program module executing means and said digital data transmitting means are constituted by a computer circuit having hardware elements including a first CPU, a second CPU, a third CPU, a memory unit commonly provided for the first, second and third CPU and a communication interface commonly provided for the first, second and third CPU,

said first CPU is adapted to use the common memory unit so as to perform the process related to the storage means and the process related to the protective control operation process performing means, respectively,

said second CPU is adapted to use the common memory unit and the common communication interface so as to perform the process related to the abnormal data information transmitting means, a receiving process for receiving the program module related to the program module executing means and the process related to the digital data transmitting means, respectively, and

wherein said third CPU is adapted to use the common memory unit so as to perform an executing process for executing the program module received by the receiving process of the second CPU.

24. An electric power system protective control system according to claim 17, wherein each of said protective control apparatus is provided with means for receiving through the communication network the precise time acquired by the acquiring means of at least one of other protective control apparatuses, and means for confirming whether or not the acquired precise time of its own protective control apparatus is accurate according to the received precise time related to at least one of other protective control apparatuses.

25. An electric power system protective control system according to claim 16, wherein at least one of said protective control apparatuses is connected to at least one of other protective control apparatuses through a communication line which is different from the communication network,

said acquiring means of at least one of other protective control apparatuses is composed of means for acquiring precise time, said at least one of other protective control means having means for superimposing a periodic signal indicating each timing of each acquired precise time on time data indicating time of each timing thereof so as to transmit a superimposition signal to the at least one of the protective control apparatus through the communication line, said super imposition signal being generated by the superimposition of the superimposing means and

wherein said acquiring means of the at least one of the protective control apparatuses is composed of means for separating the superimposition signal transmitted from at least one of other protective control apparatuses through the communication line into the periodic signal and the time data so as to gain the precise time.

26. An electric power system protective control system according to claim 17, wherein said acquiring means of each of the protective control apparatuses is provided with a first precise time acquiring unit for receiving GPS signals transmitted from a plurality of satellites so as to acquire first precise time in response to the received GPS signals, a second precise time acquiring unit for receiving a ground wave so as to acquire second precise time in response to the received ground wave and means for measuring a phase difference between the first precise time and the second precise time so as to correct the second precise time in accordance with the measured phase difference, and

said collecting means of each of the protective control apparatuses is adapted to sequentially sample the state quantities in accordance with the first precise time so as to collect the digital data, said first precise time being acquired by the first precise time acquiring unit, and when the first precise time is not acquired by the first precise time acquiring unit, said collecting means collecting the digital data by sequentially sampling the state quantities in accordance with the second precise time corrected by the correction means.

27. An electric power system protective control system according to claim 17, wherein each of said protective control apparatus is provided with means for acquiring time to be substituted for the precise time and means for correcting the substitutional time in accordance with the precise time acquired by the precise time acquiring means, and

wherein said collecting means is adapted to be sequentially sample the state quantities in accordance with the time corrected by the correcting means so as to collect the digital data when the precise time acquiring means does not acquire the precise time.

28. An electric power system protective control system according to claim 19, wherein each of said protective control apparatuses is provided with means for receiving first digital data collected by the collecting means of at least one of other protective control apparatuses through the communication network when the state of the digital data collected by the collecting means of its own protective control apparatus is changed as a result of execution of a protective control operation process by the performing means of at least one of other protective control apparatuses, means for calculating a state change of the electric quantity data of its own protective control apparatus based on the power-transmission line constant and the received digital data of at least one of other protective control apparatuses, said power-transmission line constant being stored in the power-transmission line constant storage means, and means for determining whether or not the state change of the digital data collected by the collecting means satisfies a range of a state change of the digital data so as to determine whether or not the object for the protective control of the own protective control apparatus is faulty, said digital data of the state change being calculated in accordance with the digital data of at least one of other protective control apparatuses and the power-transmission line constant.

29. An electric power system protective control system according to claim 18, wherein each of said protective control apparatuses is provided with means for changing a set value related to the protective control operation of the own protective control apparatus in accordance with a change demand transmitted from at least one of other protective control apparatuses and the monitor/control unit.

30. An electric power system protective control system according to claim 18, wherein at least one of said protective control apparatuses is provided with means for collecting, through the communication network, the digital data representing a state quantity of the electric power system at which an accident occurs, said state quantity of the electric power system at the occurrence of the accident being collected by other protective control apparatuses which detect an abnormality related to the accident, respectively, and said collected quantity data of a part of other protective control apparatuses having the absolute time at the detection of the abnormality, respectively, means for obtaining a delay state of the abnormal detection time between the part of other protective control apparatuses in accordance with the collected digital data having the absolute time at the detection of abnormality and means for estimating a distance from an accident point and a cause of the abnormality in accordance with the obtained delay state between the part of other protective control apparatuses.

31. An electric power system protective control system according to claim 16, wherein said electric power system and each of said protective control apparatuses are connected to each other through a second communication network which is different from the communication network, said state quantity related to the electric power system being supplied to each of the protective control apparatuses through the second communication network.

32. A computer-readable storage medium storing a program code for use in a protectively control of a plant, in which the plant has an input device for inputting a state quantity related to the plant therefrom and an opening/closing device for opening and closing a part of the plant, said program code comprising:

a first step of causing a computer to acquire a precise time;

a second step of causing said computer to sample the state quantity inputted from the input device according to the acquired precise time so as to convert the state quantity into digital data;

a third step of causing said computer to add the precise time at each sampling timing to the digital data so as to transmit the digital data to a communication network, said digital data each having the sampled precise time;

a fourth step of causing said computer to perform a control operation according to the digital data transmitted through the communication network;

a fifth step of causing said computer to transmit a control command with respect to the opening/closing device through the communication network in response to a result of the control operation of the fourth step;

a sixth step of causing said computer to receive, through the communication network, the control command with respect to the opening/closing device; and

a seventh step of causing said computer to control an operation of the opening/closing device according to the received control command, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

33. A computer-readable storage medium according to claim 32, wherein said storage medium is composed of first, second and third memories, and wherein said first, second and third steps of the program code are stored in the first memory, said forth and fifth steps of the program code are stored in the second memory and said sixth step of the program code is stored in the third memory.

34. A computer-readable storage medium storing a program code for use in a control of a plant, in which the plant has an input device for inputting a state quantity related to the plant therefrom and an opening/closing device for opening and closing a part of the plant, and the program code is used for generating digital data having a precise time according to the state quantity, performing a control operation according to the digital data and controlling an operation of the opening/closing device in accordance with a result of the performed control operation, said program code comprising:

a step of causing a computer to acquire the precise time;

a step of causing said computer to sample the state quantity inputted from the input device according to the acquired precise time so as to convert the state quantity into digital data; and

a step of causing said computer to add the precise time at each sampling timing to the digital data so as to transmit the digital data to a communication network, said digital data each having the sampled precise time, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

35. A computer-readable storage medium storing a program code for use in a control of a plant, in which the plant has an input device for inputting a state quantity related to the plant therefrom and an opening/closing device for opening and closing a part of the plant, and the program code is used for generating digital data having a precise time according to the state quantity, performing a control operation according to the digital data and controlling an operation of the opening/closing device in accordance with a result of the performed control operation, said program code comprising:

a step of causing a computer to perform a control operation according to the digital data transmitted through a communication network; and

a step of causing said computer to transmit a control command through the communication network in response to a result of the control operation of the performing step, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

36. A computer-readable storage medium storing a program code for use in a control of a plant, in which the plant has an input device for inputting a state quantity related to the plant therefrom and an opening/closing device for opening and closing a part of the plant, and the program code is used for generating digital data having a precise time according to the state quantity, performing a control operation according to the digital data and controlling an operation of the opening/closing device in accordance with a result of the performed control operation, said program code comprising:

a step of causing a computer to receive, through a communication network, a control command with respect to the opening/closing device; and

a step of causing said computer to control an operation of the opening/closing device according to the received control command, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

37. A computer-readable storage medium storing a program code for use in a protectively control of an electric power system, in which the electric power system has an input device for inputting a state quantity related to the electric power system therefrom and an opening/closing device for opening and closing a part of the electric power system, said program code comprising:

a step of causing a computer to acquire a precise time;

a step of causing said computer to sample the state quantity inputted from the electric power system according to the acquired precise time so as to convert the state quantity into digital data;

a step of causing said computer to add the precise time at each sampling timing to the digital data so as to transmit the digital data to a communication network, said digital data each having the sampled precise time;

a step of causing said computer to receive the digital data transmitted through the communication network, said digital data each having the sampled precise time; and

a step of causing said computer to time-sequentially arrange the received digital data each having the sampled precise time in accordance with the precise time of each of the received digital data, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

38. A computer-readable storage medium storing a program code for use in a protective control of an electric power system by a plurality of computers including protective control computers, in which the plurality of computers are connected to each other through a communication network so that data communication is permitted, and the protective control computers are disposed in correspondence with equipment devices of the electric power system, respectively, said program code comprising:

a step of causing each of the protective control computers to acquire a precise time;

a step of causing each of the protective control computers to sample a state quantity related to an equipment device of the electric power system according to the acquired precise time so as to convert the state quantity into digital data, said equipment device being an object of protective control of each of the protective control computers;

a first judgement step of causing each of the protective control computers to judge whether or not the objective equipment device is faulty based on the converted digital data so as to perform a protective control operation according to a result of the judgement of the first judgement step;

a second judgement step of causing each of the protective control computers to judge whether or not the objective equipment device and other at least one of the equipment devices are faulty based on the converted digital data, said other at least one of the equipment devices being not an object of each of the protective control computers;

a step of causing each of the protective control computers to, when the judgement of the second judgement means is made that at least one of the objective equipment device and other one of the equipment devices is fault, add the precise time to the converted digital data at each sampling timing so as to record the digital data each having the sampled precise time;

a step of causing each of the protective control computers to transmit the digital data recorded by the record step to the communication network, said transmitted digital data having the sampled precise time;

a step of causing at least one of the computers to receive the digital data transmitted through the communication network from each of the protective control computers, said received digital data having the sampled precise time; and

a step of causing at least one of the computers to time-sequentially arrange the received digital data according to the sampled precise time thereof each of the protective control computers, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

39. A computer-readable storage medium storing a plurality of program codes for use in a protective control of an electric power system, in which said plurality of program codes correspond to a plurality of computers, respectively, the plurality of computers are connected to each other through a communication network so that data communication is permitted, and the electric power system has a plurality of equipment devices which are objects of protective control of the protective control computers, respectively, said each of the program codes comprising:

a step of causing a corresponding computer to acquire a precise time;

a step of causing said corresponding computer to sample a state quantity related to the corresponding equipment device at predetermined periods in accordance with the acquired precise time so as to convert the sampled state quantity into first digital data;

a transmitting step of causing said corresponding computer to add the precise time to each first converted digital data at each sampling timing so as to transmit the first digital data each having the sampled precise time to the communication network;

a step of causing said corresponding computer to receive second digital data having the sampled precise time transmitted from another at least one of the computers through the communication network;

a step of causing said corresponding computer to time-sequentially arrange the received second digital data in accordance with the sampled precise time of each second received digital data; and

a step of causing said corresponding computer to perform a protective control operation by using one of the first digital data converted by the converting step and the second digital data time-sequentially arranged by the arranging step, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

40. A computer-readable storage medium storing a plurality of program codes for protective controlling an electric power system by a protective control system according to a state quantity inputted from the electric power system, in which the protective control system has a plurality of computers and a circuit for acquiring a precise time, the plurality of program codes correspond to the plurality of computers, respectively, and the plurality of computers are connected to each other through a communication network so that data communication is permitted, said each of the program codes comprising:

a step of causing a corresponding computer to sequentially sample the state quantity inputted from the electric power system at a same timing as a timing of other computers in accordance with the precise time so as to collect digital data; and

a step of causing said corresponding computer to add the precise time at each sampling timing to the collected digital data so as to sequentially store the digital data each having the sampled precise time, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

41. A method of protectively controlling a plant, in which the plant has an input device for inputting a state quantity related to the plant therefrom and an opening/closing device for opening and closing a part of the plant, said method comprising the steps of:

acquiring a precise time;

sampling the state quantity inputted from the input device according to the acquired precise time so as to convert the state quantity into digital data;

adding the precise time at each sampling timing to the digital data so as to transmit the digital data to a communication network, said digital data each having the sampled precise time;

performing a control operation according to the digital data transmitted through the communication network;

transmitting a control command with respect to the opening/closing device through the communication network in response to a result of the control operation of the performing step;

receiving, through the communication network, the control command with respect to the opening/closing device; and

controlling an operation of the opening/closing device according to the received control command, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

42. A method of protectively controlling an electric power system having a plurality of equipment devices, the method comprising the steps of:

acquiring a precise time;

sampling state quantities inputted from the respective equipment devices at a same timing in accordance with the precise time so as to collect digital data; and

adding the precise time at each sampling timing to the collected digital data of the respective equipment devices so as to sequentially store the digital data each having the sampled precise time, wherein

said precise time has an accuracy of substantially 1 μ

s to 100 ns.

43. A control system which receives and processes an analog state quantity of a plant, said control system comprising:

a plurality of state quantity input/output units, which do not comprise a control operation function, each state quantity input/output unit of said plurality of state quantity input/output units comprising;

precise time acquiring means for acquiring a precise time by GPS,

converting means for converting the state quantity of the plant which must be controlled into digital data by sampling the state quantity in accordance with the acquired precise time, and

transmitting means for adding said precise time by GPS of sampling to obtained digital data to generate digital data having the precise time so as to transmit data having the precise time to a communication network;

an opening/closing device comprising;

control-command receiving means for receiving, through said communication network, a control command for opening/closing the connections among units provided for the plant which must be controlled, and

operation-state communicating means for communicating a state of operation of said opening/closing device to said communication network; and

a protective operation unit comprising;

calculating means for performing operations for carrying out control in accordance with digital data having the precise time and the state of the operation of said opening/closing device, and

a control-command issuing means for issuing, through said communication network, a control command to said opening/closing device in accordance with results of control operations performed by said calculating means,

wherein a hardware configuration and a software configuration are commonly provided for said respective state quantity input/output units.

44. The control system according to claim 43, wherein said plant is one of an industrial plant, a public plant, and a power generation plant and said state quantity of said plant controls said plant.

45. An electric power system protective control system which receives a state quantity of an electric power system to protectively control the electric power system, said electric power system protective control system comprising:

a plurality of state quantity input/output units, which do not comprise a protective control operation function, each state quantity input/output unit of said plurality of state quantity input/output units comprising;

precise time acquiring means for acquiring a precise time by GPS,

converting means for converting the analog state quantity of the electric power system into digital data by sampling the state quantity in accordance with the acquired precise time, and

transmitting means for adding a precise time of sampling to obtained digital data to generate digital data having the precise time so as to transmit digital data having the precise time to a communication network;

an opening/closing device comprising;

control-command receiving means for receiving, through said communication network, a command for controlling opening/closing of the connections among systems provided for the electric power system, and

operation-state communicating means for communicating a state of operation of said opening/closing device to said communication network; and

a protective operation unit comprising;

protective operation means for performing protective control operations in accordance with digital data having the precise time and the state of the operation of said opening/closing device, and

control-command issuing means for issuing, through said communication network, a control command to said opening/closing device in accordance with results of protective control operations performed by said protective operation means,

wherein a hardware configuration and a software configuration are commonly provided for said respective state quantity input/output units.

46. An electric power system protective control system according to claim 45, wherein

said state quantity input/output unit comprises:

self diagnosing means for diagnosing a state of the operation thereof, and

self diagnosis result transmitting means for communicating a result of self-diagnosis to said communication network, and

said opening/closing device comprises;

self-diagnosis result receiving means for receiving the result of the self-diagnosis through said communication network, and

opening/closing control means for controlling an opening/closing operation of said opening/closing device in accordance with an operation control command received by said control-command receiving means of said opening/closing device, and as a result of self-diagnosis received by said self-diagnosis result receiving means, it does not transmit an operation control command to a blocking operation unit of said opening/closing device so as to lock an operation control of opening/closing when it is determined that a hardware configuration of said state quantity input/output unit is faulty.

47. An electric power system protective control system according to claim 45, wherein said converting means provided for each of the plurality of state quantity input/output units performs sampling at predetermined periods while said converting means are being synchronized with one another in accordance with the precise time acquired by said precise time acquiring means to convert each of state quantities into digital data, said transmitting means provided for each of said plurality of state quantity input/output units adds precise time of sampling to a plurality of digital data converted by said converting means to transmit the plurality of digital data each having the precise time to said communication network, and

said protective operation means comprises:

receiving means for receiving the plurality of digital data each having the precise time and the state of the operation transmitted through said communication network,

arranging means for time-sequentially arranging the received plurality of digital data each having the precise time for each of said state quantity input/output units in accordance with added precise time, and

protective-control calculating means for performing protective-control operation processes in accordance with digital data which has time-sequentially been arranged by said arranging means.

48. An electric power system protective control system according to claim 47, wherein

said precise time acquiring means, said converting means and transmitting means are constituted by a computer circuit having hardware elements including a CPU and memory units,

wherein said computer circuit including said CPU comprises:

self-diagnosing means for self-diagnosing a state of operation of said computer circuit including said hardware elements such as said memory units, and

communicating means for communicating a result of diagnosis performed by said diagnosing means to said communication network,

wherein said electric power system protective control system further comprises;

self diagnosis result receiving means for receiving a result of self-diagnosis performed by said diagnosing means and communicated through said communication network, and

locking means for locking control of the operation of said opening/closing device in accordance with the result of the self-diagnosis received by said self diagnosis result receiving means, and

wherein said opening/closing devices further comprises;

said self diagnosis result receiving means, and

said locking means.

49. An electric power system protective control system according to claim 45, wherein

said state quantity input/output unit and said opening/closing device are provided for each electric site of a plurality of electric sites dispersedly disposed in a plurality of units,

said precise time acquiring means, said converting means and said transmitting means are provided for each of said state quantity input/output unit of said electric site of said plurality of electric sites,

said operation-state communicating means and said control-command receiving means are provided for each of said opening/closing device of said electric site of said plurality of electric sites,

said protective operation means and said control-command issuing means are provided for at least one of said electric site of said plurality of electric sites which are dispersedly disposed,

said communication network comprises a first communication network in a local area constituted in each electric site, and a second communication network for widely connecting said plurality of electric sites disposed dispersedly to one another,

said converting means provided for each of said plurality of state quantity input/output units in said plurality of electric sites samples the state quantities of a corresponding state quantity input/output unit at predetermined periods while the quantities of the states are being synchronized with one another in accordance with the precise time acquired by said precise time acquiring means to convert each of the sampled state quantities into digital data, said transmitting means provided for each of said plurality of state quantity input/output units in said plurality of electric sites adds the precise time of sampling to a plurality of digital data converted by said converting means to transmit a plurality of digital data each having the precise time to said second communication network through said first communication network, and

said protective operation means disposed in said electric site comprises:

receiving means for receiving the plurality of digital data each having the precise time and the state of the operation transmitted through said first communication network and said second communication network,

arranging means for time-sequentially arranging the plurality of the received digital data each having the precise time in accordance with the added precise time, and

protective control means for performing protective control operation processes in accordance with the digital data which have time-sequentially been arranged by said arranging means.

50. An electric power system protective control system for performing operations in accordance with a state quantity input from an electric power system to protectively control said electric power system, said electric power system protective control system comprising:

a plurality of digital protective control apparatuses, which are provided in correspondence to units of an electric power system, each digital protective control apparatus of said plurality of digital protective control apparatuses comprising;

precise time acquiring means for acquiring a precise time by GPS,

converting means for sampling an analog state quantity of said electric power system at predetermined periods in accordance with the precise time acquired by said precise time acquiring means to convert the sampled analog state quantity into digital data, and

digital-data transmitting means for adding precise time by GPS of sampling to digital data converted by said converting means to transmit digital data having the precise time to a communication network;

receiving means for receiving digital data having the precise time and sequentially transmitted through said communication network;

arranging means for time-sequentially arranging received digital data having the precise time in accordance with the added precise time; and

an electric-site-side system simulation apparatus comprising generating means for generating a quantity of a test state of analog data for a digital protective control apparatus which must be tested in accordance with the digital data time-sequentially arranged by said arranging means.

51. An electric power system protective control system according to claim 50, wherein

each of said converting means of each of said plurality of digital protective control apparatuses samples the state quantities of the corresponding equipment devices at predetermined periods while the quantities of the states are being synchronized with one another in accordance with the precise time acquired by said precise time acquiring means to convert each of the sampled state quantities into digital data, each of said digital-data transmitting means provided for each of said plurality of digital protective control apparatuses adds the precise time of sampling to the plural digital data converted by said converting means so as to transmit digital data each having the precise time to said communication network,

said receiving means receives the plural digital data each having the precise time and transmitted through said communication network, and

said arranging means time-sequentially arranges the plurality of the received digital data each having the precise time for each of said plurality of digital protective control apparatuses in accordance with the added precise time.

52. An electric power system protective control system according to claim 51, further comprising:

display means for displaying a digital data group time-sequentially arranged by said arranging means.

53. An electric power system protective control system comprising:

a plurality of digital protective control apparatuses configured to protect an electric power system;

a communication network configured to connect the plurality of digital protective control apparatuses to one another such that data communication is permitted, wherein

each of said plurality of digital protective control apparatuses comprises;

precise time acquiring means for acquiring a precise time,

converting means for, at predetermined periods, sampling a state quantity of a unit which must be protected in accordance with the precise time acquired by said precise time acquiring means and converting the sampled state quantity into digital data,

protective control calculating means for determining whether or not an equipment device which must be protected is faulty in accordance with digital data converted by said converting means to perform protective control operation processes in accordance with a result of a determination,

determining means for performing a determination individually from a faulty determining function of said protective control calculating means whether or not the equipment device which must be protected and an equipment device which is not protected are faulty in accordance with digital data converted by said converting means,

recording means for adding a precise time of sampling to record digital data having the precise time when a determination is made in accordance with a result of the determination made by said determining means from at least one of the equipment device which must be protected and the equipment device which is not protected, and

digital-data transmitting means for transmitting digital data having the precise time and recorded by said recording means to said communication network;

receiving means connected to said communication network and arranged to receive a plurality of digital data each having the precise time transmitted from each of said digital protective control apparatuses through said communication network; and

arranging means for time-sequentially arranging the plurality of received digital data each having the precise time for each of said digital protective control apparatuses in accordance with the added precise time.

54. An electric power system protective control system according to claim 53, further comprising:

display means for displaying a digital data group time-sequentially arranged by said arranging means.

55. An electric power system protective control system according to claim 53, further comprising:

generating means for generating a quantity of a test state for a digital protective control apparatus which must be tested in accordance with a digital data group time-sequentially arranged by said arranging means.

56. An electric power system protective control system comprising:

a plurality of digital protective control apparatuses for protecting an electric power system; and

a communication network for connecting the plurality of digital protective control apparatuses to one another such that data communication is permitted, wherein

each of said plurality of digital protective control apparatuses comprises;

precise time acquiring means for acquiring a precise time,

converting means for, at predetermined periods, sampling a state quantity of a unit which must be protected in accordance with the precise time acquired by said precise time acquiring means and converting the sampled state quantity into digital data,

digital-data transmitting means for adding a precise time of sampling to digital data converted by said converting means to transmit digital data having the precise time to said communication network,

receiving means for receiving digital data having the precise time sequentially transmitted from digital-data transmitting means of another digital protective control apparatus through said communication network,

arranging means for time-sequentially arranging a plurality of digital data each having the precise time and received by said receiving means in accordance with the added precise time, and

protective control calculating means for performing protective control operation processes in accordance with one of digital data converted by said converting means and digital data time-sequentially arranged by said arranging means.

57. An electric power system protective control system comprising:

a plurality of protective control apparatuses configured to perform operations in accordance with an analog state quantity relating to a unit which must be protected and supplied from an electric power system to protectively control said electric power system; and

a communication network through which said plurality of protective control apparatuses are connected to each other such that data communication is permitted, wherein

each of said plurality of protective control apparatuses comprises;

periodic-signal acquiring means for, which is also precise time acquiring means for acquiring a precise time by GPS, acquiring signals at substantially constant periods,

digital-data collecting means for sequentially sampling an analog state quantity relating to said electric power system at the same timing as that of another protective control apparatus in accordance with the periodic signals acquired by said periodic-signal acquiring means to collect digital data, and

storage means for adding precise time by GPS of sampling which is performed in response to the periodic signals to digital data collected by said digital-data collecting means to sequentially store digital data having the precise time.

58. An electric power system protective control system according to claim 57, further comprising a display control apparatus connected to said communication network and arranged to remotely monitor and control a state of the operations of the plurality of protective control apparatuses,

wherein each of said plurality of protective control apparatuses comprises:

protective control operation means for performing protective control operation processes in accordance with digital data to determine whether or not abnormal data is detected, and

abnormal-data-detection notice issuing means for issuing a notice of generation of abnormal data including abnormal-data detected time to said display control apparatus when abnormal data is detected as a result of the protective control operation processes performed by said protective control calculating means,

wherein said display control apparatus further comprising program module transmitting means for transmitting a program module for collecting digital data before and after abnormal-data detected time to the plurality of protective control apparatuses through said communication network by using a predetermined transmitting passage when the notice of generation of abnormal data including abnormal-data detected time has been transmitted from a predetermined protective control apparatus of the plurality of protective control apparatuses,

wherein each of said plurality of protective control apparatuses further comprising;

receiving means for receiving the program module transmitted through said communication network to execute the program module, and

transmitting means for transmitting digital data having the precise time before and after abnormal-data detected time to said display control unit in accordance with the executed program module, and

wherein said display control apparatus comprises accident-point orienting means for orienting an accident point related to detection of abnormal data in accordance with digital data having the precise time before and after the abnormal-data detected time and transmitted from each of said plurality of protective control apparatuses.

59. An electric power system protective control system according to claim 57, wherein each of said plurality of protective control apparatuses comprises:

power-transmission line constant measuring means for operating in accordance with a program module transmitted from said display control apparatus through said communication network, for measuring a power-transmission line constant, for reading a predetermined precise time of the precise time stored in storage means of an own-protective control apparatus together with digital data, and for measuring the power-transmission line constant by using digital data of said own-protective control apparatus to which the predetermined precise time has been added, and digital data of other protective control apparatuses,

power-transmission line constant storage means for storing the measured power-transmission line constant, and

calculating means for calculating a ranging impedance relating to an object which must be protected by said own-protective control apparatus in accordance with the measured power-transmission line constant.

60. An electric power system protective control system according to claim 58, wherein said storage means stores digital data having the precise time in a period of time spanning from transmission of the notice of generation of abnormal data to said display control apparatus to transmission of digital data having the precise time before and after the time at which abnormal data has been generated to said display control apparatus.

61. An electric power system protective control system according to claim 57, further comprising:

a display control apparatus connected to said communication network and arranged to remotely monitor and control a state of the operations of the plurality of protective control apparatuses, wherein

each of said plurality of protective control apparatuses comprises power-flow information calculating means for calculating power-flow information related to said electric power system based on an electric power, an ineffective electric power and electric currents in accordance with digital data stored in said storage means and having the precise time, and said power-flow information calculating means adds a time at which digital data has been collected, which is a source for power-flow information, to communicate power-flow information having the collection time to said display control apparatus through said communication network, and

said display control apparatus further comprises stable-state determining means for determining a state of stability of said electric power system in accordance with power-flow information communicated from each of said plurality of protective control apparatuses through said communication network.

62. An electric power system protective control system according to claim 58, wherein a hardware circuit including a plurality of CPU, memories commonly provided for the plurality of CPU and a communication interface commonly provided for the plurality of CPU constitutes said storage means of each of said plurality of protective control apparatuses, said protective control calculating means, said abnormal-data-detection-time communicating means, said program module executing means and said digital-data transmitting means, and

wherein a first CPU of the plurality of CPU uses said common memory to perform a process associated to said storage means and a process associated to said protective control operation unit and a second CPU of the plurality of CPU uses said common memory and said common communication interface to perform a process associated to said abnormal-data-detection-time communicating means, a process associated to said program module executing means and a process associated to said digital-data transmitting means.

63. An electric power system protective control system according to claim 58, wherein a hardware circuit including a plurality of CPU, memories commonly provided for the plurality of CPU and a communication interface commonly provided for the plurality of CPU constitutes said storage means of each of said plurality of protective control apparatuses, said protective control calculating means, said abnormal-data-detection-time communicating means, said program module executing means and said digital-data transmitting means,

a first CPU of the plurality of CPU uses said common memory to perform the process associated to said storage means and the process associated to said protective control calculating means,

a second CPU of the plurality of CPU uses said common memory and said common communication interface to perform the process associated to said abnormal-data-detection-time communicating means, a program module receiving process of said program module executing means and the process associated to said digital-data transmitting means, and

a third CPU of the plurality of CPU uses said common memory to perform a process for executing the program module received by said second CPU.

64. An electric power system protective control system according to claim 57, wherein each of said plurality of protective control apparatuses comprises:

precise time receiving means for receiving, through said communication network, the precise time acquired by said precise time acquiring means of another protective control apparatus, and

precise time confirming means for confirming whether or not the precise time acquired by said own protective control apparatus is accurate in accordance with the received precise time of said another protective control apparatus.

65. An electric power system protective control system according to claim 57, wherein at least one protective control apparatus of the plurality of protective control apparatuses is connected to said another protective control apparatus through a communication line which is different from said communication network,

said periodic-signal acquiring means of said another protective control apparatus is said precise time acquiring means for acquiring the precise time, said another protective control apparatus comprises superimposition transmission means for superimposing a signal representing each timing constituting the precise time acquired by said precise time acquiring means and time data representing time of each timing to communicate a result of superimposition to said at least one protective control apparatus through said communication line, and

said periodic-signal acquiring means of said at least one protective control apparatus is separating means for separating the superimposition signal transmitted from said another protective control apparatus through said communication line into a signal representing each timing and time data representing time of the timing to obtain the precise time including the periodic signal.

66. An electric power system protective control system according to claim 57, wherein said precise time acquiring means of each of said plurality of protective control apparatuses comprises:

a first precise time acquiring unit configured to receive GPS signals transmitted from a plurality of satellites to acquire a first precise time in response to the received GPS signals,

a second precise time acquiring unit configured to receive a ground wave to acquire a second precise time in response to the received ground wave, and

correction means for measuring a phase difference between the first precise time acquired by said first precise time acquiring unit and the second precise time acquired by said second precise time acquiring unit to correct the second precise time in accordance with the measured phase difference, and

wherein said digital-data collecting means sequentially samples the state quantities in accordance with the first precise time acquired by said first precise time acquiring unit to collect digital data, and when the first precise time cannot be acquired by said first precise time acquiring unit, said digital-data collecting means collects digital data by sequentially sampling the state quantities in accordance with the second precise time corrected by said correction means.

67. An electric power system protective control system according to claim 57, wherein each of said plurality of protective control apparatus comprises:

time acquiring means for acquiring time to be substituted for the precise time, and time calibrating means for calibrating the time in accordance with the precise time acquired by said precise time acquiring means, and

wherein said digital-data collecting means sequentially samples the state quantities in accordance with the time calibrated by said time calibrating means to collect digital data when said precise time acquiring means cannot acquire the precise time.

68. An electric power system protective control system according to claim 59, wherein each of said plurality of protective control apparatuses comprises:

receiving means for receiving digital data collected by said digital-data collecting means through said communication network when the state of digital data collected by said digital-data collecting means of said own protective control apparatus has been changed as a result of execution of a protective control operation by other protective control calculating means,

calculating means for calculating a change in the state of electric quantity data of the own protective control apparatus in accordance with the power-transmission line constant stored in said power-transmission line constant storage means and digital data of said another protective control apparatus received, and

determining means for determining whether or not the change of the state of digital data collected by said digital-data collecting means satisfies a range of state change of digital data operated in accordance with digital data of said another apparatus and the power-transmission line constant to determine whether or not the object which must be protected by the own apparatus is faulty.

69. An electric power system protective control system according to claim 58, wherein each of said plurality of protective control apparatuses comprises changing means for changing a setting value related to the protective control operation of the own protective control apparatus in accordance with a system change requirement communicated from at least one of said another protective control apparatus and said display control apparatus.

70. An electric power system protective control system according to claim 58, wherein each of predetermined protective control apparatuses of the plurality of protective control apparatuses comprise:

collecting means for collecting, through said communication network, digital data representing a state quantity of said electric power system from a plurality of protective control apparatuses from which an abnormality has been detected owing to occurrence of an accident in a state in which absolute time of detection of the abnormality is added to digital data,

delayed means for obtaining a delayed state of the abnormal detection time among the plurality of protective control apparatuses from which the abnormality has been detected in accordance with collected digital data having the absolute time in an event of detection of the abnormality, and

estimating means for estimating a distance from an accident point and a cause of the abnormality in accordance with the obtained delayed state.

71. An electric power system protective control system according to claim 57, wherein said electric power system and each of said plurality of protective control apparatuses are connected to each other through a second communication network which is different from said communication network, and a state quantity of said electric power system is supplied to each of said plurality of protective control apparatus through said second communication network.

72. A storage medium comprising:

a control program stored therein to control a plant incorporating a plurality of units including a state quantity input/output unit and an opening/closing device, with a plurality of computers including at least a first computer provided for said state quantity input/output unit and a second computer provided for said opening/closing device, wherein

said control program comprises;

causing a precise time to be acquired by said first computer,

causing said first computer to sample a state quantity of said state quantity input/output unit at predetermined periods in accordance with the precise time to convert the sample state quantity into digital data,

causing said first computer to add precise time of sampling to digital data having the precise time to transmit digital data having the precise time to a communication network,

causing said second computer to communicate a state of the operation of the opening/closing device to said communication network,

causing at least one of the plurality of computers to receive digital data having the precise time and transmitted through said communication network and the state of the operation so as to perform operations in accordance with received digital data having the precise time and the state of the operation,

causing said at least one computer to transmit an operation control command to said opening/closing device to said communication network in accordance with a result of the operations,

causing said second computer to receive the operation control command transmitted through said communication network, and

causing said second computer to operate said opening/closing device in accordance with the received operation control command.

73. The storage medium according to claim 72, wherein said plant is an electric power system.

74. A storage medium comprising a protective control program stored therein to protect a plurality of units provided for an electric power system by using a plurality of protective control computers, said protective control program comprising:

causing each of said plurality of protective control computers to acquire a precise time;

causing each of said plurality of protective control computers to sample a state quantity of an equipment device which must be protected at predetermined periods in accordance with the precise time to convert the sampled state quantity into digital data;

causing each of said plurality of protective control computers to add the precise time of the sampling to converted digital data to transmit digital data having the precise time to a communication network;

causing each of said plurality of protective control computers to receive digital data having said precise time transmitted from other digital protective control apparatus;

causing each of said plurality of protective control computers to receive digital data having the precise time and sequentially transmitted from said other digital protective control apparatus through said communication network;

causing each of said plurality of protective control computers to time-sequentially arrange the plurality of the received digital data each having the precise time in accordance with the added precise time; and

causing each of said plurality of protective control computers to execute protective control operation processes in accordance with either converted data or digital data which has time-sequentially been arranged.