GB2505832A

GB2505832A - Communication apparatus

Info

Publication number: GB2505832A
Application number: GB1322405.0A
Authority: GB
Inventors: Kosuke Ogata
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2011-11-22
Filing date: 2011-11-22
Publication date: 2014-03-12
Anticipated expiration: 2031-11-22
Also published as: JP5579331B2; KR20140024055A; GB2505832A8; JPWO2013076807A1; GB201322405D0; WO2013076807A1; GB2505832B; KR101529444B1

Abstract

A measurement value packet that informs a measurement value having been measured and a time synchronization packet that is to be used for time synchronization are transmitted and received between a merging unit (MU) (100) and an integrated electronic device (IED) (200). A computation unit (102) of the MU (100) and a computation unit (202) of the IED (200) each perform a processing of the measurement value packet, while a communication unit (101) of the MU (100) and a communication unit (201) of the IED (200) each perform a processing of the time synchronization packet independently of the computation unit (102, 202).

Description

DESCRIPTION

Title of Invention: COMMUNICATION APPARATUS

S Technical Field

[0001] The present invention relates to a time synchronization technique.

In the following, a time synchronization technique in a computerized power system protection system in an electric power substation will be primarily described as

an example.

Background Art

[0002] A power system protection system is a system that protects a power system from an electrical malfunction caused by an earth fault, a disconnection or the like in an electric power substation or the like.

As shown in Fig. 7, the power system protection system includes one or more 1VIU (Merging Unit) 100 and an TED (Integrated Electronic Device) 200, and each MU is connected to the TED 200 with a communication line 300.

The MV 100 is connected to an instrument transformer 400 located in the power system (for example, a power transmission line 500, etc.). The MU 100 periodically samples current and voltage (hereinafter collectively referred to as current-voltage) of the power system via the instrument transformer 400, and periodically transmits the sampled current-voltage values of the power system to the lED 200.

The lED 200 is a computation unit that collects the sampled current-vohage values (hereinafter simply referred to as measurement values) from the MU 100 to determine a malfunction of the power system.

Each of the communication lines 300 between each of the MUs 100 and the TED 200 is independent of one another.

[0003] The lED 200 compares differences in current-voltage values at the same time at different locations in the power system, and thereby detects occurrence of a malfunction.

For example, in dctcction of a disconnection in the power transmission line, the MUs 100 measure currcnt waveforms at both ends of the power transmission linc, and the TED 200 identifies a disconnected point based on phase differences of thc current waveforms.

Thus, each of the MUs 100 is required to sample current-voltage values with the same timing as the other MUs 100.

A method for realizing this is to use clocks keeping the same time through time synchronization between the lED 200 and the MUs 100, and to perform sampling with the same timing based on thcse clocks.

In time synchronization, the lED 200 distributes the current time to each of the MUs 100 so that the clocks in the respective MUs 100 keep the same time.

[0004] Conventionally, in the power system protection system, the communication line bctwccn the TED 200 and the MU 100 is realized with direct connection of analog inputs and outputs or a manufacturer proprietary network. In rcccnt years, the adoption of Ethernet (registered trademark) has been increasing duc to demand for cost reductioll.

With the adoption of Ethernet (registered trademark) between the lED and thc MU, a method using an Ethernet (registered trademark) linc has also been adopted for time synchronization.

With this method, transmission of current-voltage measurement values and time synchronization can he performed with the same Ethernet (registered trademark) line, so that the cost of lines can be reduced.

As an example of the method for realizing time synchronization with packet communication using the Ethernet (registered trademark) line, there is IEEE 1588 described in Non-Patent Literature 1.

[0005] Fig. 8 shows the basis of time synchronization according to IEEE 1588.

One computer A transmits a packet storing thc current time (hereinafter referred to as a sync packet) to another computer B. The computer B extracts the current time from the sync packet received from the computer A, and corrects its own clock To compensate a delay in clock correction due to a delay in packet transmission between the computers A and B, packets (namely, a delay_req packet and a delay resp packet) are exchanged between the computers A and B, and a response time Y and a response time X are computed. The response time Y is tile time it takes for the packets to be exchanged between the computers A and B, and the response time X is the processing delay time in the computer A. The response time X is the time from when the computer A receives the delay_req packet to when the computer A transmits the delay_resp packet in response to thc received delay_req packet.

The response time Y is the time from when the computer B transmits the delay req packet to when thc computer B receives the delay rcsp packet.

The computer B adds a transmission delay time D = (Y -X) / 2 to the clock to correct the time.

In this way, in time synchronization according to IEEE 1588, in order td notify the current time and measiare a transmission delay, it is necessary to transmit or receive at least 3 packets (exchange packets at least 1.5 times).

[0006] As a method for implementing time synchronization, there is a software method in which software installed in a terminal performs time distribution and delay measurement, and there is a hardware method in which hardware provided in a terminal performs time distribution and delay measurement. The latter method provides more accurate time synchronization.

In this specification, the description will he provided primarily focused on the latter hardware method.

However, the time synchronization technique described in this specification may be adapted for a software method.

[0007] As a time synchronization technique by the hardware method, there is a technique disclosed in Patent Literature 1.

Referring to Figs. 7 and 8, a configuration of the lED 200 and the MU 100 and a time synchronization procedure for implementing time synchronization with the Ethernet (registered trademark) line using the technique of Patent Literature 1 will be described.

[0008] The lED 200 in Patent Literature 1 is composed of a communication part for communicating with the MU 100 and a computation part that determines a malfimction of the power system based on measurement values received from the MU 100 (not illustrated).

The MU I 00 is composed of a communication part for communicating with the lED 200 and a computation part that samples current-voltage from the instrument transformer 400 located in the power system and transmits the sampled values to the lED 200 via the communication part (not illustrated).

The computation part of the lED 200 and the computation part of the MU 100 are both provided with a function to receive a packet from the communication part and interpret the packet and a fUnction to generate an arbitrary packet.

[0009] Between the TED 200 and the MU 100 of Patent Literature 1, the computation part of the IvffJ 100 periodically generates measurement value packets for notifying current-voltage measurement values, and the communication part transmits the measurement value packets to the lED 200. Iii the TED 200, the computation part analyzes the measurement values indicated in the measurement value packets to determine a malftmction of the power system.

In between transmitting and receiving of the measurement value packets, the sync packet, the delay_req packet and the delay resp packet shown in Fig. 8 are transmitted and received between the TED 200 and the MU 100.

In transmitting and receiving of the sync packet, the delay req packet, and the delay resp packet, the lED 200 assumes a role of the computer A of Fig. 8, and the MU assumes a role of the computer B of Fig. 8.

Specifically, the following operations are performed in transmitting and receiving of the sync packet, the delay_req packet, and the delay resp packet.

Hereinafter, the sync packet, the delay_req packet, and the delay_resp packet will be collectively referred to as a "timc synchronization packet".

[0010] The computation part of the lED 200 generates a sync packet to notify the current time in the TED 200, and outputs the generated sync packet to the communication part. The communication part transmits the sync packet to the MU 100.

In the MU 100, the communication part receives the sync packet, stores the current time indicated in the sync packet, and outputs the sync packet to the computation part.

Upon inputting the sync packet, the computation part of the MU 100 generates a delay_req packet and outputs the delay_req packet to the communication part. The communication part transmits the delay_req packet to the lED 200.

At this time, the communication part of the MU 100 stores the transmitted time of the delay_req packet.

In lED 200, the coninunication part receives the delay_req packet, and outputs the delay_req packet to the computation part.

The conmmnicatjon part of the lED 200 stores the received time of the delay_req packet.

Upon inputting the delay_req packet, the computation part of the lED 200 generates an empty delay_resp packet (delay resp packet with an empty payload), and outputs the empty delay_resp packet to the communication part.

Upon inputting the empty delay resp packet, the communication part writes the processing delay time in the lED 200 (corresponding to the response time X of Fig. 8) in the payload of the delay_resp packet, and transmits to the MU 100 the delay_resp packet in which the processing delay time is written.

In the MU 100, the communication part receives the delay_resp packet, calculates a time difference between the received time of the delay resp packet and the transmitted time of the delay_req packet (corresponding to the response time Y of Fig. 8), calculates the transmission delay time D of Fig. 8 based on the calculated time and the processing delay time indicated in the delay resp packet, calculates a time correction value based on the transmission delay time D and the current time notified by the sync packet, and updates the time of an internal clock.

Citation List Patent Literature [0011] Patent Literature: JP 2006-81194 A N on-Patent Literature [0012] Non-Patent Literature 1: "IEEEI 588", The Institute of Electrical and Electronics Engineers, 24 July 2008

Disclosure of Invention

Techilical Problem [0013] The technique of Patent Literature 1 adopts the method in which the computation part of the lED or the MU generates an empty time synchronization packet, and the communication part intercepts the empty time synchronization packet and sets time information in the empty time synchronization packet.

With such a method, the time synchronization sequence shown in Fig. 8 is neither started nor advanced unless the computation part generates a time synchronization packet.

[0014] Generally, after performing the time synchronization sequence between the TED and the IVITJ, if the time synchronization sequence is not performed newly, the synchronization between the clocks of the lED and the MU will be gradually lost.

This is because each oscillator, such as a crystal, used as a clock has an inherent deviation in frequency per unit time, and the frequency per unit time of the oscillator of the lED does not completely coincide with thc frequency per unit time of the oscillator of the MU.

For this reason, to keep the deviations between the clocks of the ILL) and the MU small, it is necessary to repeat the time synchronization sequence at short interva!s [001 5] Thus, in the method that requires processing by the computation part for starting and advancing the time synchronization sequence as in the teclmique of Patent Literature 1, in order to repeat the time synchronization sequence at short intervals, the computation part is required to repeat processing for time synchronization at short intervals.

This may impose a load on the computation part, which adversely affects processing for system protection (processing to analyze measurement values to determine whether a malfunction has occurred in the power system).

[0016] The present invention addresses the above-described point, and primarily aims to constantly synchronize thc time between apparatuses to be time-synchronized without imposing any load on the computation part.

Solution to Problem [00171 A communication apparatus according to the present invention has a computation part and a communication part, the communication part transmitting and receiving a packet, the communication apparatus communicating a measurement value packet to notify a measured measurement value and a timc synchronization packet for time synchronization with a packct communication destination apparatus, wherein 1 5 the computation part performs processing for the measurement value packet, and the communication part performs processing for the time synchronization packet independently of the computation part.

Advantageous Effects of Invention [0018] According to thc present invention, a communication part performs processing for a time synchronization packet independcntly of a computation part, so that execution of a time synchronization sequence does not impose any load on the computation part.

Hence, thc time synchronization sequence can be rcpcated at short intervals without imposing any load on the computation part, and the time can be constantly synchronized between a communication apparatus and a packet communication destination apparatus.

Brief Description of Drawings

[0019] Fig. 1 is a diagram showing an example configuration of an lED and an MU according to first and sccond embodiments; Fig. 2 is a diagram showing an example configuration of a communication part according to the first and second embodiments; Fig. 3 is a diagram showing a time synchronization procedure between the lED and the MU according to the fir st embodiment; Fig. 4 is a diagram showing the time synchronization procedure between the lED and the MU according to the first embodiment; Fig. 5 is a diagram showing the timc synchronization procedure between thc lED and the MU according to the second embodiment; Fig. 6 is a diagram showing the time synchronization procedure between the lED and the MU according to the second embodiment; Fig 7 is a diagram showing an example connection configuration of a power system protection system; Fig. 8 is a diagram showing an examp'e of a time synchronization sequence; Fig. 9 is a diagram showing an example of a measurement value packet according to the first and second embodiments; Fig. 10 is a diagram showing an example of a sync packet according to the first and second embodiments; Fig. Ills a diagram showing an example of a delay_req packet according to the first and second embodiments; Fig. 12 is a diagram showing an example of a delay resp packet according to the first and second embodiments; Fig. 13 is a diagram showing an example configuration of a conventional communication part; Fig. 14 is a diagram showing a time synchronization procedure between a conventional IFD and MU.

Fig. 15 is a diagram showing the time synchronization procedure between the conventional TED and MU; Fig. 16 is a diagram showing the time synchronization proccdurc between the conventional TEl) and MU; and Fig. 17 is a diagram showing an exampic hardware configuration of the lED 1 0 and the MU according to the first and second emhodimcnts.

Description of Preferred Embodiments

[0020] First Embodiment Fig. 1 shows an example internal configuration of an MU 100 and an TED 200 according to this embodiment.

The MU 100 has a communication part 101 and a computation part 102. The lED 200 has a communication part 201 and a computation part 202.

In this embodiment, as a method for implementing time synchronization, an example using a hardware method will be described.

Aceordingy, the communication part TOT and the computation part 102 of the MU 100 arc separate hardware components.

Likewise, the communication part 20! and the computation part 202 of thc lED are separate hardware components.

The communication part 101 of the MU 100 will also be described as the "MU communication part 101", and the computation part 102 of the MU 100 will also be described as the "MU computation part 102". Ii

The communication part 201 of the lED 200 will also he described as the "lED communication part 201", and the computation part 202 of the TED 200 will also he describcd as the "lED computation part 202".

[0021] As shown in Fig. 7, the MU 100 and the lED 200 according to this embodiment are connected to each other with a communication line 300.

As described with reference to Patent Literature 1, the MU computation part 1 02 periodically generates measurement valuc packets for notifying current-voltage measurement values. The MU communication part 101 transmits the measurement value packets to the LED 200. Tn the LED 200, the TED computation part 202 analyzes the measurement values indicated in the measurement value packets to dctcrminc a malfhnction of the power system.

In between transmitting and receiving of the measurement value packets, a sync packet, a delay_req packet, and a delay resp packet (examples of a time synchronization packet) shown in Fig. 8 are transmitted and received between the TED 20(1 and the MU 100.

In transmitting and receiving of the sync packet, the delay_req packet, and the delay_resp packet, the lED 200 assumes a role of a computer A of Fig. 8, and the MB assumes a role of a computer B of Fig. 8.

[0022] In this embodiment, it is thc TED communication part 201, not the TED computation part 202, that gcncratcs a sync packet, and transmits the generated sync packet to the MU IOU.

In the MV 100, the MU communication part 101 receives the sync packet, and stores the current time indicated in the received sync packet.

It is the MV communication part 101, not the MU computation part 102, that generates a delay_req packet, and transmits the generated delay_req packet to the TED 200.

At this time, the MU communication part 101 stores the transmitted time of the delay_req packet.

In the TED 200, it is the lED coniinunication part 201, not the lED computation part 202, that receives the delay_req packet, generates an empty delay resp packet (delay resp packet with an empty payload) in response to the delay_req packet, writes the processing delay time in thc lED 200 (corresponding to a response time X of Fig. 8) to the payload of the generated cmpty delay resp packet, and transmits to the vHJ 100 the delay resp packet in which the processing delay time is written.

In the MU 100, the MU communication part 101 rcccivcs the delay_resp packet, calculates a time difference between the received time of the delay resp packet and the transmitted time of the delay_req packet (corresponding to a response time Y of Fig. 8), calculates a transmission delay time D of Fig. 8 based on the calculated time and the processing delay time indicated in the delay resp packet, calculates a time 1 5 correction value based on the transmission delay time D and the current time notified by the sync packet, and updates the time of an internal clock of the MU 100.

[0023] As described above, in the lED 200 according to this embodiment, unlike the techniquc of Patcnt Litcrature 1, the TED communication part 201 generates the sync packet and transmits thc sync packet to the MU 100 independently of the lED computation part 202, without any instruction from the TED computation part 202 or control by the TED computation part 202 such as an input of an empty packet.

Upon receiving the delay_req packet, the lED communication part 201 generates the delay resp packet and transmits the delay req packet to the MU 100 indcpcndently of the lED computation part 202, without outputting the delay_req packet to the TED computation part 202 and without any instruction from the lED computation part 202 or control by the TED computation part 202 such as an input of an empty packet.

Furthermore, in the MU 100 according to this embodiment, unlike the technique of Patent Literature 1, the MU communication part 101 generates the delay_req packet and transmits the delay_req packet to the lED 200 independently of the MU computation part 102, without outputting the sync packet to thc MU computation part 102 and without any instruction from the MU computation part 102 or control by the MU computation part 1 02 such as an input of an empty packet.

[00241 The MU 100 and the lED 200 arc examples of a communication apparatus and a packet communication destination apparatus.

That is, when the MU 100 operates as a communication apparatus, thc lED 200 operates as a packet communication destination apparatus. When the lED 200 operates as a cormnunication apparatus, the MU 100 opcrates as a packet communication destination device.

[0025] Fig. 2 shows an example internal configuration of the MU communication part 101 and the lED communication part 201.

[0026] Each of the MU communication part 101 and the TED communication part 201 is composed of a PHY 213 that performs processing of a first layer (physical layer) of Ethernet (registered trademark), an MAC 211 that performs processing of a second layer (data link layer), and a time synchronization part 212 that forwards (transfers) a packet not related to time synchronization between the PHY 213 and the MAC 211 and intercepts a packet related to time synchronization to perform predetermined proccssing for the intercepted packet.

Further, the time synchronization part 212 is composed of a packet routing part 221, a time synchronization processing part 222, and a time synchronization packet generation part 223.

Depending on the packet identifier of a packet flowing between the P1-TY 213 and the MAC 211, the packet muting part 221 forwards or intercepts the packet.

The time synchronization processing part 222 receives time synchronization packets, and performs processing for the received time synchronization packets.

In the MU 100, the processing for the time synchronization packets includes, for example, storing the current time notified by the sync paekct, storing the transmitted time of the delay_req packet, calculating a time correction value, and updating the internal clock. In the TED 200, the processing for the time synchronization packets includes, for example, calculating the processing delay time.

The time synchronization packet generation part 223 generates time synchronization packets according to instructions from the time synchronization processing part 222.

More specifically, the time synchronization packet generation part 223 of the MU 100 generates the delay_req packet, and the time synchronization packet generation part 223 of the lED 200 generates the sync packet and the delay resp packet.

[0027] lb clearly demonstrate differences between this embodiment and Patent Literature 1, Fig. 13 shows an example configuration of the communication part of the MU and the lED of Patent Literature 1.

In Patent Literature 1, time synchronization packets are generated in the computation part. Thus, the time synchronization packet generation part 223 does not exist in the communication part of Patent Literature 1, as shown in Fig. 13.

Except for the time synchronization packet generation part 223, the configuration shown in Fig. 13 is the same as that shown in Fig. 2.

[0028] Figs. 9 to 12 show forniats of packets to be communicated between the MU and the lED 200 according to this embodiment.

[0029] As shown in Figs. 9 to 1 2, packets used in this embodiment include measurement value packets (Fig. 9) for periodically transferring measurement values and time synchronization packets for transferring time information for time synchronization. As with IEEE 1588, three types of time synchronization packets are used, namely the sync packet (Fig. 10), the delay_rcq packet (Fig. 11), and the delay resp packet (Fig. 12).

Referring to the measurement value packet, 41 is a transmission destination MAC (Media Access Control) address, 42 is a transmission source MAC address, 43 is an identifier indicating that the packet type is the measurement value packet, 44 is transmission data of a measurement value which is a payload, and 45 is a checksum of the entire packet.

Referring to the sync packet, 51 is a transmission destination MAc address, 52 is a transmission source MAC address, 53 is an identifier indicating that the packet type is the time synchronization packet, 56 is an identifier indicating that the packet type is the sync packet, 54 is transmission data of time information (information on the current time) which is a payload, and 55 is a checksum of the entire packet.

Referring to the delay req packct, 61 is a transmission destination MAC address, 62 is a transmission source MAC address, 63 is an identifier indicating that the packet type is the time synchronization packet, 66 is an identifier indicating that the packet type is the delay_req packet, 64 is transmission data of timc information which is a payload (not requisite), and 65 is a. checksum of the entire packet.

Referring to the delay_rcsp packet, 71 is a transmission destination MAC address, 72 is a transmission source MAC address, 73 is an identifier indicating that the packet type is the time synchronization packet, 76 is an identifier indicating that the packet type is the delay_resp packet, 74 is transmission data of time information (information on the processing delay time in the lED 200) which is a payload, and 75 is a checksum of the entire packet.

Note that the identifiers 43, 53, 56, 63, 66, 73, and 76 shown in Figs. 9 to 12 are identifiers used for identifying packet types, and represent examples of type identifier data.

[0030] Referring to Figs. 3 and 4, a time synchronization proccdure between the lED and the MU 100 according to this embodiment will now be described.

[0031] (0) Preconfiguration I 0 As preconfiguration, thc lED computation part 202 configures the packet routing part 221 of the time synchronization part 212 such that, upon detection oia packet having the packet identifier of the measurement value packet, the packet routing part 221 notifies the time synchronization processing part 222 that the measurement value packet has been detected.

[0032] (1) Time synchronization (transmission of the sync packet) (Fig. 3) The following description starts from a point when the lED communication part 201 of the TED 200 receives a measurement value packet from the MU 100.

First, the packet routing part 221 of the time synchronization part 212 in the TED communication part 201 reads the packet identifier of the packet transferred from thePFIY2l3.

In this case, the packet identifier indicating the measurement value packet can be read. Thus, immediately after forwarding (transferring) the entire measurement value packet to the MAC 211, the packet routing part 221 notifies the time synchronization processing part 222 that the measurement value packet has been received (S 101).

Then, upon being notified by the packet routing part 221 that the measurement value packet has been received, the time synchronization processing part 222 instructs the time synchronization packet generation part 223 to generate a sync packet (S 102).

The time synchronization packet generation part 223 generates the sync packet having the packet identifiers of time synchronization and sync and storing time information (information oil the current time in the lED 200) in the transmission data (Fig. 10), and transfers the generated sync packet to the packet routing part 221 (S 103).

The packet routing part 221 transfers the sync packet transferred from the time synchronization packet gcncration part 223 to the PI-IY 213 (Si 04).

The PRY 213 transfers the sync packet transferred from the packct routing part 221 to the PHY 213 of the MU 100 (S105).

The PHY 213 of the MU 100 transfers the packet transmitted from the lED 200 to the time synchronization part 212 (S 106).

The packet routing part 221 of the time synchronization part 212 reads the packet identifier of the packet transferred from the PHY 213.

In this case, the packet identifier indicating the time synchronization packet can be read. Thus, the transferred time synchronization packet is transferred to the time synchronization processing part 222 (S 107).

The time synchronization processing part 222 receives the time synchronization packet transferred from thc packet muting part 221, identifies the packet as the sync packet based on the packet identifier, and reads the time information (information on the current time in the lED 200) from the transmission data of the sync packet (S108).

Then, the time synchronization processing part 222 stores the time information (information on the current time in the TED 200) read from the transmission data of the sync packet (to be continued to Fig. 4).

[0033] (2) Time synchronization (transmission of the delay req packet) (Fig. 4) The time synchronization processing part 222 of the MU 100 receives the time synchronization packet (sync packet) from thc lED 200, and instructs the time synchronization packet generation part 223 to generate a delay req packet (S 109).

The time synchronization packet generation part 223 gcncrates the delay req packet having thc packet identifiers of time synchronization and dclay_req and storing arbitrary information in the transmission data (Fig. 11), and transfers the generated delay_req packet to the packet routing part 221 (Silo). The packet routing part 221 transfers the delay req packet to the PITY 213 (S 11 1).

The transmission data of the delay_req packet may be any data, and may be predetermined time information or meaningless information.

Then, as in the case of transmission of the sync packet, the PHY 213 of the MU transmits the delay req packet to the PHY 213 of the lED 200. The packet routing part 221 of the TED 200 identifies the received packet as the time synchronization packet by detecting the packet identifier, and transfers the received time synchronization packet to the time synchronization processing part 222 (S 112 to S 114).

In the MU 1 00, the time synchronization proccssing part 222 is notified by the PHY 213 of the transmitted time of the delay_req packct, and stores the transmitted time of the delay_req packet.

Alternatively, the time synchronization processing part 222 of the MU 100 is notified by the packet routing part 221 of the time when the packet routing part 221 transferred the delay req packet to the P1-IY 213 as the transmitted time of the delay_req packet, and stores the transmitted time of the dclay_req packet.

[00341 (3) Time synchronization (transmission of the delay_resp packet) (Fig. 4) The time synchronization processing part 222 of the lED 200 identifies the received packet as the delay_req packet by detecting the packet identifier of the time synchronization packet, and instructs the time synchronization packet generation part 223 to generate a delay_resp packct (S 115).

The time synchronization packet generation part 223 generates the delay resp packet having the packet identifiers of time synchronization and delay resp and storing time information (information on the processing dclay time in the TED 200) in tile transmission data (Fig. 12), and transfers the generatcd delay resp packet to the packet routing part 221 (Sl16).

The processing dclay time in the lED 200 (colTesponding to the responsc timc X of Fig. 8) is the time from when the lED 200 receives thc dclay req packet to when the lED 200 transmits the delay resp packet in response to the dclay_rcq packet.

The time synchronization packet generation part 223 of the lED 200 may writc in the delay resp packet, as the processing delay time, thc time from when the packet routing part 221 detects receipt of the delay_req packet to when the time synchronization packet generation part 223 actually generates the delay_resp packet, for

example.

Ahernatively, the time synchronization packet generation part 223 may derive from statistics information the average timc from when the delay_req packet is received to when the delay_resp packet is transmittcd, and may write this average time in the delay resp packct as the processing delay time.

Then, the packet routing part 221 of the TED 200 transfers thc dclayresp packet to the PHY 213 (S117).

The PITY 213 transmits the delay_resp transferred from the packet routing part 221 to the PHY 213 ofthc MV 100 (S1l8).

The PHY 213 of the MU 100 transfers the packet transmitted from the lED 200 to the time synchronization part 212 (Si 19).

The packet routing part 221 of the time synchronization part 212 reads the packet identifier of the packet transferred from thc PHY 2i3.

In this case, the packet identifier indicating the time synchronization packet can be read. Thus, thc transferred time synchronization packet is transferred to thc time synchronization proccssing part 222 (S 120).

The timc synchronization processing part 222 receives the time synchronization packet transferred from the packet muting part 221, identifies the rcceived packet as the delay resp packet based on the packet identifier 54, and reads the time information (information on the processing delay time in the lED 200) from thc transmission data of the delay_resp packet (S121).

The time synchronization processing part 222 calculates a time difference between the received timc of the delay resp packet and the transmitted time of the delay_req packet (corresponding to the response time Y of Fig. 8), calculates the transmission delay time D of Fig. 8 based on the calculated time and the processing delay time indicated in the deiay_resp packet, calculates the time correction value based on the transmission delay time D and the current time notified by the sync packet, and updates the internal clock.

For example, the internal clock is updated using as the current time of the MU the time obtained by adding thc transmission delay time D to the current time notified by the sync packet.

The received time of the delay resp packet may be, for example, the time when the time synchronization processing part 222 determines that the delay_resp packet has been input (time of S 120).

Alternatively, it maybe arranged that every time a packet is received from the lED 200, the PHY 213 stores the received time of the packet. Then, upon detecting receipt of the delay resp packet, the time synchronization processing part 222 may inquire of the PHY 213 about the received time of the delay resp packet, and the time notified by the PHY 213 may be used as the received time of the delay resp packet.

[0035] As shown in the section of "TRANSMISSION OF MEASUREMENT VALUE" of Fig. 3, in transmitting and receiving of the measurement value packet, the MU computation part 102 generates the measurement value packet, the MU communication part 101 transmits the measurement value packet to the TED 200, and the TED communication part 201 receives the measurement value packet and outputs the measurement value packet to the lED computation part 202.

As described above, the lED computation part 202 analyzes the measurement values and determines whether or not thcrc is a malfunction in the power system.

[0036] As described above, in this embodiment, the lED communication part 201 autonomously generates a sync packet and transmits the sync packet to the MU 100, independently of the operation of the lED computation part 202.

Upon receiving the delay_req packet, the lED communication part 201 autonomously generates a delay resp packet and transmits the delay resp packet to the MU 100 independently of the operation of the lED computation part 202 without outputting the delay_req packet to tile lED computation part 202.

Furthermore, in the MU 1 00 according to this embodiment, the MU communication part 101 autonomously generates a delay_req packet and transmits the delay_req packet to the TED 200 without outputting a sync packet to the MU computation part 102 and independently of the operation of the MU computation part 102.

[0037] On the other hand, in the technique of Patent Literature 1, the operation of the lED communication part depends on the operation of the computation part, and the operation of the MU communication part depends on the operation of the computation part.

For comparison with the TED 200 and the MU 100 according to the first embodiment, an example of the operation of the TED 200 and thc MU 100 in the technique of Patent Literature 1 will be briefly described with reference to Figs. 14 to 16.

[0038] (1) Time synchronization (transmission of the sync packet) (Fig. 14) As with Fig. 3, the description here starts from a point when the communication part of the lED 200 receives a measurement value packet from the MU 100.

Afler completing periodic transmission of a measurement vaine, the computation part of the lED 200 generates a packet having the packet idcntifiers of time synchronization and sync and empty data content (payload), and transfers the packet to the MAC 211 (Si).

The MAC 211 transfers the packet transferred from the computation part to the time synchronization part 212 (S2).

The packet routing part 221 of the time synchronization part 212 reads the packet identifier of the packet transferred from the MAC 211.

In this ease, the packet identifier indicating the time synchronization packet can be read. Thus, the packet is transferred to the time synchronization processing part 222 (S3).

The time synchronization processing part 222 receives the packet transferred from the packet routing part 221, identifies the packet identifier as sync, writes time information (information on the current time in the TED 200) in the transmission data of the packet, and transfers the packet to the packet routing part 221 (S4).

The packet routing part 221 transfers the packet transferred from the time synchronization processing part 222 to the PITY 213 (S5).

The PHY 213 transmits the packet transferred from the packet routing part 221 to the PHY 213 of the MU 100 (S6).

The PHY 213 of the MU 100 transfers tile packet transmitted from the lED 200 to the time synchronization part 212 (S7).

Thc packet routing part 221 of the time synchronization part 212 reads the packet identifier of the packet transferred from the PRY 213.

In this case, the packet identifier indicating the time synchronization packet can be read. Thus, the packet is transferred to the time synchronization processing part 222 (S8).

The time synchronization processing part 222 receives the packet transferred from the packet routing part 221, identifies the packet identifier as sync, reads the time information (information on the current time in the TED 200) from the transmission data of the packet, and transfers the packet to the packet routing part 221 (59).

The time synchronization processing part 222 also stores the time information (information on the current time in the lED 200) read from the transmission data of the sync packet.

The packet routing part 221 transfers the sync packet transferred from the time synchronization processing part 222 to the MAC 211 (S 1(J).

The MAC 21 T transfers the sync packet to the computation part (S 11) (to be continued to Fig. 1 5).

[00391 (2)Timc synchronization (transmission of the dcTay req packet) (Fig. 15) The computation part of the MU 100 receives the sync packet from the lED 200, generates a packet (delay_req packet) having the packet identifiers of time synchronization and delay req and empty transmission data, and transfers the packet to the MAC 211 (S12).

The MAC 211 transfers the delay_req packet having the empty transmission data to the packet routing part 221 (S 13). The packet muting part 221 transfers the delay_req packet having the empty transmission data to the time synchronization processing part 222 (S14).

Thc time synchronization processing part 222 writes predetermined time information in the transmission data of the delay_req packet or leaves the transmission data as empty, and transfers to the packet routing part 221 the delay_req packet in which the predetermined time information is written in the transmission data or the transmission data remains as empty (S 15).

Then, the packet routing part 221 transfers the delay_req packet to the PRY 213 (S 16). The PHY 213 transfers the delay_req packet to the PHY 213 of the lED (S17).

In the MU 100, the time synchronization processing part 222 is notified by the PHY 213 of the transmitted time of the delay_req packet and stores the transmitted time of the delay_req packet in S17.

In the TED 200, the PRY 213 transfers the received packet to the packet routing part 221 (S 18). The packet routing part 221 identifies the received packet as the time synchronization packet by detecting the packet identifier, and transfers the received time synchronization packet to the time synchronization processing part 222 (S 19).

The time synchronization processing part 222 identifies the received packet as the delay_req packet by detecting the packet identifier of the time synchronization packet, instructs the packet routing part 221 to transfer the packet to the computation part, and transfers the delay req packet to the packet routing part 221 (S20).

The packet routing part 221 transfcrs the delay req packet to the MAC 211 (S21). The MAC 211 transfers the delay req packet to the computation part (S22) (to be continued to Fig. 16).

[0040] (3) Time synchronization (transmission of the delay resp packet) (Fig. 16) The computation pail of the lED 200 generates a packet having thc packet identifiers of time synchronization and delay resp and empty data content, and transfers thc packet to the MAC 211 (S23).

The MAC 211 transfers the packet transfcrrcd from the computation part to the time synchronization part 212 (S24).

The packet routing part 221 of the time synchronization part 212 reads the packet identifier of the packet transferred from the MAC 21 t.

In this case, the packet identifier indicating the time synchronization packet can be read. Thus, the packet is transferred to the time synchronization processing part 222 (S25).

The time synchronization processing part 222 receives the packet transferred from the packct routing part 221, identifies the packet identifier as dclay_resp, writes time information (information on the processing delay time in the lED 200) in the transmission data of the packet, and transfers the packet to the packet routing part 221 (S26).

The packet routing part 221 transfers the packet transferred from the time synchronization processing part 222 to the PITY 213 (S27).

The PHY 213 transfers the packet transferred from the packet routing part 221 to the PHY 213 of the MU 100 (S28).

The PHY 213 of the MU 100 transfers the packet transferred from the TED 200 to the time synchronization part 212 (S29).

S In this case, the packet identifier indicating the time synchronization packet can be read. Thus, the packet is transferred to the time synchronization processing part 222 (S30).

The time synchronization processing part 222 receives the packet transferred from the packet routing part 221, identifies the packet identifier as delay resp, reads the time information (information on the processing delay time in the lED 200) from the transmission data of the packet, and transfers the delay resp packet to the packet routing part 221 (S31).

The packet routing part 221 transfers the delay resp packet transferred from the time synchronization processing part 222 to the MAC 211 (S32).

The MAC 211 transfers the delay resp packet to the computation part (S33).

Then, the computation part of the MU 100 calculates a time difference between the received time of the delay resp packet and the transmitted time of the delay_req packet (corresponding to the response time Y of Fig. 8), calculates the transmission delay time D of Fig. 8 based on the calculated time and the proccssing delay time indicated in the delay resp packet, calculates the time correction value based on the transmission delay time D and the current time notified by the sync packet, and updates the internal clock.

[0041] As described above, according to this embodiment, the time synchronization part 212 of the lED 200 detects the passing of the measurement value packet transmitted periodically, and autonomously starts time synchronization (independently generates and transmits the sync packet).

Upon receiving the time synchronization packet, the time synchronization part 212 of the lED 200 or the MU 100 indepcndcnfly generates and transmits the time synchronization packet to be transmitted next.

With this arrangement, the time synchronization processing can be performed without depending on the processing of the computation parts 101 and 202 of the MU and the lED 200.

As described abovc, time synchronization is performed autonomously between the respectivc time synchronization parts 212. Thus, time synchronization is carried out without depending on the processing of thc computation parts 102 and 202, so that the load on the computation parts 102 and 202 is reduced.

That is, the processing for the received lime synchronization packet and the generation of the time synchronization packet to be transmitted are performed by the communication parts 101 and 201. Thus, execution of the time synchronization sequence does not impose any load on the computation parts 102 and 202.

Therefore, the time synchronization sequence can be repeated at short intervals without affecting the processing for system protection performed by the computation parts 102 and 202, and the time car be constantly synchronized between the TED 200 and the MU 100.

Since thc load on the computation parts 102 and 202 is reduced, the computation parts 102 and 202 can be implemented with processor devices less costly than those conventionally used, and cost-saving effects can be expected.

Execution of time synchronization does not require any processing by the computation parts 102 and 202, so that effects can also bc cxpected with regard to facilitation of software design of the computation parts 102 and 202.

Furthermore, it is possible to omit transfer of received time synchronization packets from the communication parts 101 and 201 to the computation parts 102 and 202 and transfer of empty time synchronization packets from the computation parts 1 02 and 202 to the cormnunication parts 101 and 201. As a result, the processing time in the lED 200 and the MU 100 can be reduced, and power consumption can be reduced.

[00421 Second Embodiment In thc first embodiment, the packet routing part 221 of thc time synchronization part 212 starts to forward (transfer) a packet transmitted from an external source after receiving and detecting the packet identifier.

An alternative method may be considered in which the packet routing part 221 starts to forward (transfcr) a packet to the time synchronization processing part 222 and the MAC 211 immediately after starting to receive the packet, without identifying the packet twe.

With this arrangement, it is not necessary to wait until the packet routing part 221 receives the packet identifier As a result, the time required for communication for time synchronization can be reduced.

In this case, however, the packet routing part 221 forwards (transfers) a packet unconditionally Thus, a time synchronization packet is transferred to the MAC 211, ncccssitating the processing by the computation part (the MU computation part 102 or the lED computation part 202) to identify and discard a time synchronization packet that arrived at the MAC 211.

[0043] Accordingly, in this embodiment, in parallel with forwarding (transfer) of a packet, the packet routing part 221 detects the packct identifier of the packet. If the packet is a time synchronization packet, the packet routing part 221 terminates the forwarding (transfer) of the packet to the MAC 211 before completion.

In this case, the time synchronization packet that arrives at the MAC 211 results in an error in a checksum test.

Then, the MAC 211 discards the packet with the checksum error and does not notify the computation part (the MU computation part 1 02 or the lED computation part 202) that the packet has been received, in this way, it is possible to eliminate the processing by the computation part to identify and discard a time synchronization packet arriving at the MAC 211.

[0044] The operation according to this embodiment will be described specifically.

[0045] The configuration of the lED 200 and the MU 100 is the same as in thc first 1 0 embodiment.

However, there are some differences in fhnctionality.

As described above, upon starting to receive a packet, the packet routing part 221 immediately forwards (transfers) the packet to the time synchronization processing part 222 and the MAC 211 without identifying the packet type.

The time synchronization processing part 222 is provided with an additional function for detecting the packet identifier of a packet forwarded from the packet routing part 221 and starting time synchronization if a predetermined packet identifier is detected.

[0046] Referring to illustrations in Figs. 5 and 6, the time synchronization procedure between the lED 200 and the MU 100 will now be described.

[0047] (0) Preconfiguration As preconfiguration, the computation part 202 of the TED 200 configures the time synchronization processing part 222 of the time synchronization part 212 to start time synchi-onization upon receipt of a packet having the packet identifier of the measurement value packet.

[0048] (1) Time synchronization (transmission of the sync packet) (Fig. 5) As with Fig. 3, the description here starts from a point when the communication part 201 of the lED 200 receives a measurement value packet from the MU 100.

The time synchronization processing part 222 of the time synchronization part 212 reads the packet identifier of the packet transferred from the packet routing part 221.

In this case, thc packet identifier indicating the measurement value packet can be read. Thus, the time synchronization processing part 222 instructs the time synchronization packet generation part 223 to generate a sync packet (S201).

The time synchronization packet generation part 223 generates the sync packet having the packet identifiers of time synchronization and sync and storing time information (information on the current time in the lED 200) in the transmission data (Fig. 10), and transfers the generated sync packet to the packet routing part 221 (S202).

The packet routing part 221 transfers the sync packet transferred from the time synchronization packet generation part 223 to the PHY 213 (S203).

The PHY 213 transmits the sync packet transferred from the packet routing part 221 to thc PRY 213 of the MU 100 (S204).

The PRY 213 of the MU 100 transfers the packet transmitted from the TED 200 to the time synchronization part 212 (S205).

The packet routing part 221 of the time synchronization part 212 transfers the packet transferred from the PRY 213 to the time synchronization processing part 222 and the MAC 211 (S206, S208).

In parallel with the transfer of the packet, the packet routing part 221 detects the packet identifier, and as a resuit identifies the packet being transferred to the MAC 211 as the time synchronization packet, and thus terminates the transfer to the MAC 211 before completion (S208).

The time synchronization processing part 222 receives the packet transferred from the packet routing part 221, identifies the packet as the sync packet based on the packet identifier, and reads the time information (information on the current time in the lED 200) from the transmission data of the sync packet (S207).

The time synchronization packet that has reached the MAC 211 (the timc synchronization packet of which the transfer to the MAC 211 has been tenninatcd before completion) results in an error in a checksum test by the MAC 211.

The MAC 211 discards the time synchronization packet with the checksum error, and does not notify the MU computation part 102 that the time synchronization packet has been received (to be continued to Fig. 6).

[0049] (2) Time synchronization (transmission of the delay req packet) (Fig. 6) S209 through S213 are the same as S109 through S113 of Fig. 4 presented in the first embodiment.

That is, the time synchronization processing part 222 of the MU 100 receives the time synchronization packet (sync packet) from the TED 200, and instructs the time synchronization packet generation part 223 to generate a delay_req packet (S209).

Furthermore, the time synchronization packet generation part 223 generates the delay_req packet having the packet identifiers of time synchronization and delay_req and storing arbitrary information in the transmission data (Fig. [I), and transfers the generated delay_req packet to the packet routing part 221 (S2 10). The packet routing part 221 transfers the delay req packet to the PHY 213 (S2 11).

Furthermore, the PRY 213 of the MU 100 transmits the delay_req packet to the PRY 213 of the lED 200 (S212). The PRY 213 of the lED 200 transfers the received packet to the packet routing part 221 (S213).

The packet routing part 221 transfers the packet transferred from the PHY 213 to the time synchronization processing part 222 and the MAC 211 (S214, S2 15).

In parallel with the transfer of the packet, the packet routing part 221 detects the packet identifier, and as a result identifies the packet as the time synchronization packet, and thus terminates the transfer to the MAC 211 before completion (S21 5).

The timc synchronization packet that has reached thc MAC 211 (the time synchronization packct of which the transfer to the MAC 211 has been terminated before completion) results in an error in a checksum test by the MAC 211.

The MAC 211 discards the time synchronization packet with the checksum error, and does not notify the MU computation part 102 that the time synchronization packet has been received.

[0050] (3) Time synchronization (transmission of the delay resp packet) (Fig. 6) S216 through S220 are the same as S115 through S119 of Fig. 4 presented in the first embodiment.

That is, the time synchronization processing part 222 of the lED 200 detects the packet identifier of the time synchronization packet, and thus identifies the packet as the delay_rcq packet, and instructs the time synchronization packet generation part 223 to gencratc a delay resp packet (S216).

The time synchronization packet generation part 223 generates the delay resp packet having the packet identifiers of time synchronization and delay resp and storing time information (information on the processing delay time in the TED 200) in the transmission data (Fig. 12), and transfers the generatcd delay resp packet to the packet routing part 221 (S217).

Then, the packet routing part 221 of the TED 200 transfers the delay resp packet to the PHY 213 (S21 8).

The PHY 213 transmits the delayjesp packet transferred from the packet routing part 221 to the PHY 213 ofthe MU 100 (S219).

The PHY 213 of the MU 100 transfers the packet tnmsrnitted from the lED 200 to the time synchronization part 212 (S220).

Then, the packet routing part 221 transfers the packet transferred from the PHY 213 to the time synchronization processing part 222 and the MAC 211 (S221, S222).

In parallel with the transfer of the packet, the packet muting part 221 detects the packet identifier, and as a result identifies the packet as the time synchronization packet, and thus terminates the transfer to the MAC 211 before completion (S222).

The time synchronization packet that has reached the MAC 211 results in an error in a checksum test.

The MAC 211 discards the packet with the checksum error, and does not notitS' the MU computation part 102 that the packet has been received.

As in the first embodiment, the time synchronization processing part 222 calculates the transmission delay time D of Fig. 8, calculates the time correction value based on the transmission delay time D and the current time notified by the sync packet, and updates the internal clock.

[00511 When a measurement value packet is rcceived in the TED 200, the packet routing part 221 also transfers the received packet to the time synchronization processing part 222 and thc MAC 21! before detecting that the received packet is the measurement value packet (8301, 8302 of Fig. 5).

Then, when the packet routing part 221 detects that the received packet is the measurement value packet, the packet routing part 221 continues to transfer the measurement value packet to the MAC 211. Thus, the measurement value packet is transferred to the lED computation part 202 without being discarded in the MAC 211.

As a result, the lED computation part 202 analyzes the measurement value in the measurement value packet to determine whether or not a maiftinction has occurred in the power system.

[0052] As described above, in this embodiment, the communication part outputs the rcccived packet to the computation part before identifying the packet type, and if the rcccivcd packet is determined as a packet not ncccssary for the computation part (time synchronization packet) as a result of identifying the packet type, the communication part stops the output of thc packet to the computation part and discards the packet.

On the other hand, if the received packet is a packet necessary for the computation part (measurement value packet), the output of the packet to the computation part is continued, so that the computation part receives the packet.

Therefore, according to this embodiment, the packet can be output to thc computation part earlier by the time it takes for the packet type to be identified, so that processing time can be shortened.

[0053] In the first and second embodiments, the power system protection system has been described, in which the measurement unit (MU) that periodically samples current-voltage of the power system is connected via a bidirectional network cable with the computation unit (I ED) that collects sampled current-voltage values from the measurement unit to determine a malfunction of the power system, the sampled values are stored in packets and periodically transmitted from the measurement unit to the computation unit, and in between periodic transmissions of the packets (measurement value packets) storing the sampled values, time information is stored in a packet (time synchronization packet) and transmitted to perform time synchronization.

[0054] In the fir st and second embodiments, the following has been described.

The packets include at least two types, which are packets storing the sampled values and packets for time synchronization, and thc packet type of each packet can be identified by an identifier stored in each packet.

Thc communication part of each of the computation unit and the measurement unit is composed of the PRY and the MAC both of which perform network transmission processing and the time synchronization part that performs processing for timc synchronization.

The time synchronization part is composed of the packet routing part that forwards or captures a packet between the PHY and the MAC, the time synchronization part that identifies the identifier stored in the packet captured by the packet routing part and performs processing in accordance with the idcntifier, and the time synchronization packet generation part that generates a packet for time synchronization upon bcing instructed by the time synchronization processing part.

[0055] In the first and second embodiments, the following has been described.

In the time synchronization part of the computation unit or the measurement unit, when the packet i-outing part reads the packet identifier of the packet received from the PHY and as a result identifies the received packet as thc packet for time synchronization, the packet routing part transfers the packet to the time synchronization processing part.

The time synchronization processing part receives the packet transferred from the packet routing part and performs processing related to time synchronization, and also instructs the time synchronization packet generation part to generate a packet to be transmitted in response to the received packet for time synchronization.

In accordance with an instruction by the time synchronization processing part, the time synchronization packet generation part generates the packet to be transmitted in response to the reccived packet for time synchronization, and transfers the packet to the PHY through the packet routing part.

[0056] In the second embodiment, the following has been described.

In the time synchronization part of the computation unit or the measurement unit, the packet i-outing part immediately starts to transfer the packet received from the PHI to the time synchronization processing part and the MAC. In parallel with this, the packet routing part identifies the identifier of the packet received from thc PHY. If the packet is identified as thc packet for time synchronization, the packet routing part tcrminatcs the transfer of the packet to the MAC.

Thc time synchronization processing part receives the packct transferred from the packet routing part and reads thc packet identifier. If the packet is identified as thc packet for time synchronization, the time synchronization processing part performs processing related to time synchronization, and also instructs the time synchronization packet generation part to generate a packet to be transmitted in response to the received packet for time synchronization.

In accordance with an instruction by the time synchronization processing part, the time synchronization packet generation part generates the packet to be transmitted in response to the received packet for time synchronization, and transfers the packet to the PHI through thc packct routing part.

[0057] In the above, the MU and the lED used in the power systcm protection system has been described as an example.

however, the application is not limited to the power system protection system.

The configurations and proccdures described in the first and second embodimcnts may be applied to any communication apparatus that transmits and receives measurement value packets for notif'ing measured measurement values and time synchronization packets for time synchronization.

[0058] Lastly, an example hardware configuration of the MU 100 and the TED 200 S presented in the first and second embodiments will be described.

Fig. 17 is a diagram showing an example of hardware resources of the MU 100 and the lED 200 presented in the first and second embodiments.

Note that the configuration of Fig. 17 is only an example of the hardware configuration of the MU 100 and the TED 200, and the hardware configuration of the MU 100 and the lED 200 is not limited to and may be different from the configuration shown in Fig. 17.

[0059] Tn Fig. 17, each of the MU 100 and the lED 200 includes a Cpu 911 (also referred to as Centrai Processing Unit, central processing device, processing device, microprocessor, microcomputer, or processor) that executes programs.

The CPU 911 is equivalent to the MU computation part 102 and the lED computation part 202 shown in Fig. 1.

The CPU 911 is connected via a bus 912 to a ROM (Read Only Memory) 913, a RAM (Random Access Memory) 914, a communication board 915, a display device 901, a keyboard 902, a mouse 903, and a magnetic disk device 920, for cxample, and controls these hardware devices.

The communication board 915 is cquivalent to the MU communication part 101 and the TED communication part 201 shown in Fig. 1.

Furthermore, the CPU 911 may be connected to an FDD 904 (Flexible Disk Drive) and a compact disk device 905 (CDD).

Tn place of the magnetic disk device 920, a storage device such as an SSD (Solid State Drive), an optical disk device, or a memory card (registered trademark) read/write device may be used.

The RAM 914 is an example of a volatile memory Storage media of the ROM 913, the FDD 904, the CDD 905, and the magnetic disk device 920 are examples of a non-volatile memory. These are examples of a storage device.

The communication board 915, the keyboard 902, the mouse 903 and so on are examples of an input device.

The communication board 915, the display device 9(1 and so on are examples of an output device.

[0060] The communication board 915 is connected to the communication line 300 as shown inFig. 8.

The MU 100 is connected to a communication line to communicate with an instrument transformer 400 as shown in Fig. 8.

Alternatively, the communication board 915 may be connected to a LAN (local area network), the Internet, a WAN (wide area network), a SAN (storage area network) or the like.

[0061] The magnetic disk device 920 stores an operating system 921 (OS), a window system 922, programs 923, and files 924.

The programs 923 are executed by the CPU 911 using the operating system 921 and the window system 922.

[0062] The RAM 914 temporarily stores at least some of programs of the operating system 921 and application programs to be executed by the CPU 911.

The RAM 914 also stores various data required for processing by the CPU 911.

[0063] The ROM 913 stores a BIOS (Basic Input Output System) program, and the magnetic disk device 920 stores a boot program.

At start-up of the Mu 100 and the lED 200, the BIOS program in the ROM 913 and the boot program in the magnetic disk device 920 are executed, and the operating system 921 is started by the BIOS program and the boot program.

[0064j The programs 923 store programs that execute the functions of the MU computation part 102 and the lED computation part 202 described in the first and second cmbodiments.

hi the first and second embodiments, it has been described as an example that the communication parts (the MU communication part 101, the lED communication part 201) shown in Fig. 1 are hardware components separate from the communication parts (the MU communication part 101, the I ED computation part 202).

However, the packet routing part 221, the time synchronization processing part 222, the time synchronization packet generation part 223, and the MAC 211 may be implemented as programs, and the programs implementing these functions may be stored in the magnetic disk device 920.

The programs in the magnetic disk device 920 are read and executed by the CPU 911.

[0065] The files 924 store, as entries of a "file" or a "database", information, data, signal values, variable values, and parameters indicating results of processing described as "determination of.,.", "testing of, "detection of, "generation of.,.

"updating of. . . ", "setting of, "selection of, "input of, "output of and so on.

The "file" and "database" are stored in a storage medium such as a disk or a memory.

The information, data, signal values, variable values, and parameters stored in the storage medium such as the disk or memory are read out to a main memory or a cache memory by the CPU 911 through a read/write circuit.

The information, data, signal values, variable values, parameters that are read out are used for operations of the CPU such as extraction, search, reference, comparison, calculation, computation, processing, editing, output, printing, and display.

The information, data, signal values, variable values, and parameters are temporarily stored in the math memory; a register, the cache memory, a buffer memory or the like during the operations of the CPU including extraction, search, refcrcncc, comparison, calculation, computation, processing, editing, output, printing, and display.

The arrow portions in the drawings described in the first and second embodiments primarily represent inputs/outputs of data and signals The data anti signal values arc stored in the memory of the RAM 914, the flexible disk of the FDD 904, the compact disk of the CDD 905, the magnetic disk of the magnetic disk device 920, or other types of recording medium such as an optical disk, a mini disk, or a DVD.

The data and signals are transmitted online via the bus 912, signal lines, cables, or other types of transmission medium.

[0066] What is described as "part" in the first and second embodiments may be a "circuit, "device", "equipment", and may also be a "step", "procedure", or "processing".

That is, the operation of the MU 100 and the TED 200 may bc interpreted as a packet processing method based on the steps, procedures, processing shown in the drawings described in the first and second embodiments.

What is described as "part" may be implemented by firmware stored in the ROM 911 Alternatively, what is described as "part" may he implemented solely by software, or solely by hardware such as an element, a device, a substrate, or a wiring line, or a combination of software and hardware, or a combination further including firmware.

Firmware and software are stored as programs in the recording medium such as the magnetic disk, flexible disk, optical disk, compact disk, mini disk, or DVD.

The programs are read by the CPU 911 and executed by the CPU 911.

List of Reference Signs [0067] 100: MU, 101: communication part, 102: computation part, 200: WD, 201: communication part, 202: computation part, 211: MAC, 212: time synchronization part, 213: PI-1Y 221: packet routing part, 222: time synchronization processing part, 223: time synchronization packet generation part, 300: communication line, 400: instrument transformer, 500: power transmission line