System and method for realizing optical fiber differential protection communication through half-duplex channel

Abstract

A system and method for realizing optical fiber differential protection communication through a half-duplex channel comprises a master MODEM module and a slave MODEM module, and each MODEM module comprises an optical fiber receiving module, a sending cache module, a carrier wave sending module, a carrier wave receiving module, a delay compensation module, an optical fiber sending module and a management module. The optical fiber receiving module receives the message sent by the protection device, and the sending cache module caches the message, calculates the cache delay of the message and judges whether the message is an effective message; the delay compensation module reads out in a delayed manner and sends an effective message to the optical fiber sending module; and the optical fiber sending module sends the effective message to a corresponding protection device after coding processing. According to the invention, a division multiplexing method is adopted, bidirectional controllable delay communication is realized in physical upper half-duplex communication connection, the problem that the field has no optical fiber direct connection or SDH multiplexing channel condition is solved, and the problem of realizing current differential protection between transformer substations is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and more specifically, relates to a system and method for realizing optical fiber differential protection communication in a half-duplex channel. Background Art

[0002] With the continuous advancement of technology and the deepening of its application, optical fiber differential protection, as an important member of modern power system protection technology, plays an indispensable role in ensuring the safe and stable operation of the power grid with its high reliability, high sensitivity and fast action characteristics. Although this process is developing rapidly, there must be a process of one-by-one replacement in the process of product replacement.

[0003] In the current mainstream optical fiber differential protection system, the more common application methods are as follows: one is to directly connect the protection on both sides through optical fiber, which is more common in new power plants and power station equipment; the other is an optical fiber differential protection system based on the existing communication network in the station for multiplexing. Its connection method is to connect the protection to the photoelectric conversion device through optical fiber, and then connect the electrical signal to the SDH system in the station. After the protection signal is transmitted to another SDH device through the SDH network, it is converted into an optical signal by the photoelectric conversion device and sent to the protection. Based on this, it can be found that the optical fiber differential protection system either needs to lay new optical fiber or be implemented based on the existing SDH network in the station. There are also many sites that do not have these two conditions, such as there was no communication network between substations before, only power cables. Power line communication technology is mainly used for power meter reading and equipment monitoring, management and other functions. In addition, the channel environment is complex during power line communication, and noise interference and frequency fading problems are serious during transmission.

[0004] The basic idea of ​​current differential protection is that both sides of the line accurately measure the line current on their own side, and promptly transmit the sampling information on their own side to the protection of the other side of the line. The protection on both sides is based on sampling synchronization, and compares the currents on both sides of the line in real time. When the current difference meets certain conditions, the line fault is determined and the circuit breaker is tripped. The key point of the technology lies in the sampling synchronization and real-time communication on both sides.

[0005] Optical fiber differential protection has high requirements for channel delay. If the channel delay difference is large, it may cause the switch to misjudge during the switching process, thus affecting the stability and reliability of the system. If the switching time is too long, the continuity of the transmission may be interrupted, thus affecting the transmission quality and stability of the data.

[0006] Chinese patent CN104393914B proposes a multiplexing route recovery method for optical fiber differential protection devices. The scheme sets a dual-channel device at the front end of the optical fiber differential protection device, uses the ASON network management to build channel one based on the SDH optical transmission equipment network and channel two based on the large-capacity optical transmission equipment network, selects the channel with shorter delay as the working channel, and the other channel as the backup channel. This method does not require modification of the original optical fiber differential protection device. After exiting the dedicated core protection channel, dual-channel devices can be installed at both ends of the line to realize the backup route of the multiplexing mode of the single-route protection channel, and introduce the ASON optical network intelligent control plane to perform certain settings on the dual channels. However, this method is based on the on-site SDH communication network scenario, and cannot meet the scenario when there is only power line communication between stations.

[0007] Chinese patent CN113391098B proposes a light differential protection coaxial cable channel control device and a control method thereof. The scheme includes a switching device through a light differential protection coaxial cable channel control device and a control method thereof. The switching device is connected to the coaxial cable through a connector access port and connected to a tester through a test interface. The invention realizes the metal conductive connection (short circuit) function of the central conductor and shielding layer of the coaxial cable, as well as the self-loop function of this side and the other side of the channel. However, the coaxial cable channel transmission method described in this method cannot be transmitted over long distances and is more dependent on the on-site environment. Summary of the invention

[0008] In order to solve the deficiencies in the prior art, the present invention proposes an optical fiber differential protection system and method for realizing bidirectional fixed delay communication under half-duplex conditions, adopts a multiplexing method to realize bidirectional controllable delay communication in a physically half-duplex communication connection, solves the problem of lack of optical fiber direct connection or SDH multiplexing channel conditions on site, and solves the problem of realizing current differential protection between substations.

[0009] The present invention adopts the following technical solution.

[0010] The first aspect of the present invention provides a system for realizing optical fiber differential protection communication through a half-duplex channel, the system comprising a master MODEM module and a slave MODEM module, the master and slave MODEM modules both comprising: an optical fiber receiving module, a sending buffer module, a carrier sending module, a carrier receiving module, a delay compensation module, an optical fiber sending module and a management module, characterized in that:

[0011] The two protection devices are connected to the master MODEM module and the slave MODEM module respectively;

[0012] The input end of the optical fiber receiving module in the master and slave MODEM modules is connected to the corresponding protection device, receives the message sent by the protection device and verifies the message, sends the correct message to the sending buffer module, and the sending buffer module buffers the content of the message and the key information of the message in the set message format. When the sending buffer module receives the sending enable signal, it calculates the buffer delay of the message, adds the buffer delay of the message to the key information of the message, and then sends the message to the carrier sending module; the carrier sending module converts the message into a carrier; the output end of the carrier sending module is connected to the input end of the carrier receiving module of another MODEM module;

[0013] The carrier receiving module receives the carrier sent by another MODEM module, converts it into a set message format, determines whether it is a valid message, calculates the time to be forwarded, adds the key information of the valid message, and caches the valid message; the delay compensation module receives the permission signal sent by the optical fiber sending module to the delay module, reads out and sends the valid message to the optical fiber sending module; the optical fiber sending module sends the valid message to the corresponding protection device after encoding;

[0014] The management module is used to issue instructions to all other modules in the corresponding MODEM module and to count the messages received and sent by all other modules.

[0015] Preferably, the optical fiber receiving module verifies the message, specifically:

[0016] After the message is decoded by Manchester code and HDLC, a 16-bit CRC check is performed.

[0017] Preferably, the set message format is a fixed-size data frame format, and the sending cache module supports a data cache of up to 8 frames, and each frame uses a fixed-size data area and information area; the data area stores the message content; the information area stores the key information of the message, including the frame length and the time information of receiving the message.

[0018] Preferably, after the sending cache module receives the sending enable signal from the carrier sending module, it reads the earliest message cached by the sending cache module out of the cache, and calculates the difference between the time when the message is received from the protection device and the time when the message is received from the sending enable signal from the carrier sending module, as the cache delay of the message. If the cache delay exceeds the set time threshold, the message is an invalid message and is discarded. Otherwise, the message is a valid message.

[0019] If there is no valid message in the cache when the sending buffer module receives the sending enable signal from the carrier sending module, a 32-byte empty message is sent to the carrier sending module;

[0020] When the sending buffer module sends a message, if the message is less than 32 bytes, it will be padded with 0 to make up 32 bytes before sending.

[0021] Preferably, the carrier sending module of the master MODEM module sends the carrier in each set period; the carrier sending module of the slave MODEM module sends the carrier only when the sending buffer module sends a valid message.

[0022] Preferably, the carrier receiving module determines whether the converted message is a valid message, specifically:

[0023] If the carrier is converted to the set message format and the fixed flag code is set, it is determined to be an invalid message converted from an idle carrier; otherwise, the message is subjected to length and 16-bit CRC check, and the message that passes the check is a valid message.

[0024] Preferably, the carrier receiving module calculates the time to be forwarded, adds it to the key information of the valid message, and caches the valid message, specifically:

[0025] Determine whether the cache delay of the valid message in another MODEM module is greater than the set delay time. If so, discard the valid message. Otherwise, calculate the set delay time minus the cache delay of the valid message in another MODEM module as the time to be forwarded, and add the key information of the valid message at this time into the information area of ​​the valid message.

[0026] Preferably, after the delay compensation module receives the permission signal sent by the optical fiber sending module, when reading out and sending a valid message to the optical fiber sending module, it first reads out the frame length and the time to be forwarded of the valid message buffered by the carrier receiving module; when the global time reaches the time to be forwarded, the message content of the valid message is read out.

[0027] Preferably, the optical fiber sending module sends the valid message to the protection device after encoding, specifically: serializing, HDLC encoding, and Manchester code encoding the message content in the valid message.

[0028] The second aspect of the present invention provides a method for implementing optical fiber differential protection communication using a half-duplex channel of the system according to the first aspect of the present invention, comprising:

[0029] When a protection device sends a message to another protection device, the MODEM module corresponding to the protection device sending the message receives the message sent by the protection device, verifies the message, and caches the content of the message and the key information of the message in the set message format for the correct message;

[0030] When it is necessary to send, the buffer delay of the message is calculated, the buffer delay of the message is added to the key information of the message, and the message is converted into a carrier and sent to another MODEM module; and the other MODEM module sends it to the protection device corresponding to another MODEM module;

[0031] When a protection device receives a message sent by another protection device, the MODEM module corresponding to the protection device receiving the message receives the carrier sent by the other MODEM module, converts it into a set message format, determines whether it is a valid message, calculates the time to be forwarded, adds key information of the valid message, and caches the valid message; when it is necessary to send the message to the protection device receiving the message, reads out and sends the valid message, and sends the valid message to the protection device receiving the message after encoding processing.

[0032] The beneficial effects of the present invention are as follows: (1) bidirectional fixed delay communication under half-duplex conditions is realized by sending buffer and delay compensation processing, protection messages are reorganized, time stamps are added and an algorithm is used to accurately control channel delays, and length and CRC checks are performed to strictly ensure the correctness of the transmitted messages, which can meet the requirements of the optical fiber differential protection system under power line communication conditions;

[0033] (2) The global system is monitored in real time through the management interface, which is similar to transparent monitoring. The fault location can be discovered in real time, making it easier to troubleshoot the problem.

[0034] (3) Without changing the protection architecture, the carrier communication method is adopted. Through this system, long-distance protection signal transmission on the power line can be realized quickly. The transmission delay is less than 3ms, and the jitter delay is less than 5us, which meets the protection action conditions. In the 8km power cable optical fiber differential protection communication system, the bit error rate of this scheme is better than 10 -8 . BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Flowchart for encoding and decoding of communication protocols applied to optical fiber differential protection communication system;

[0036] Figure 2 The logical processing flow chart for sending a message;

[0037] Figure 3 The figure is a flow chart of the logic processing of receiving messages. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0039] like Figure 1 The embodiment 1 of the present invention provides a system for realizing optical fiber differential protection communication through a half-duplex channel, the system includes a master MODEM module and a slave MODEM module, the master and slave MODEM modules both include: an optical fiber receiving module, a sending buffer module, a carrier sending module, a carrier receiving module, a delay compensation module, an optical fiber sending module and a management module, and is characterized in that:

[0040] The two protection devices are connected to the master MODEM module and the slave MODEM module respectively;

[0041] like Figure 2 As shown, the input end of the optical fiber receiving module in the master and slave MODEM modules is connected to the corresponding protection device, receives the message sent by the protection device and verifies the message, sends the correct message to the sending buffer module, and the sending buffer module buffers the content of the message and the key information of the message in a set message format. When the sending buffer module receives a sending enable signal, it calculates the buffer delay of the message, adds the buffer delay of the message to the key information of the message, and then sends the message to the carrier sending module; the carrier sending module converts the message into a carrier; the output end of the carrier sending module is connected to the input end of the carrier receiving module of another MODEM module;

[0042] like Figure 3 As shown, the carrier receiving module receives the carrier sent by another MODEM module, converts it into a set message format, determines whether it is a valid message, calculates the time to be forwarded, adds the key information of the valid message, and caches the valid message; the delay compensation module reads out and sends the valid message to the optical fiber sending module after receiving the permission signal sent by the optical fiber sending module to the delay module; the optical fiber sending module sends the valid message to the corresponding protection device after encoding;

[0043] The management module is used to issue instructions to all other modules in the corresponding MODEM module and to count the messages received and sent by all other modules.

[0044] Preferably, the optical fiber receiving module verifies the message, specifically:

[0045] After the message is decoded by Manchester code and HDLC, a 16-bit CRC check is performed.

[0046] Preferably, the set message format is a fixed-size data frame format, and the sending cache module supports a data cache of up to 8 frames, and each frame uses a fixed-size data area and information area; the data area stores the message content; the information area stores the key information of the message, including the frame length and the time information of receiving the message.

[0047] Specifically, according to the content of the message, the message is divided into data message, synchronization message and inquiry message; the formats of the three messages are shown in the following table respectively;

[0048] Table 1 Data message structure table

[0049] TYPE Flag Data Res Len Ts Crc byte 1 25 1 1 2 2

[0050] Table 2 Synchronous message structure table

[0051] TYPE Flag Data Res Len Ts Crc Alignment byte 1 10 1 1 2 2 15

[0052] Table 3 Inquiry message structure

[0053] TYPE Flag Data Res Len Ts Crc Alignment byte 1 6 1 1 2 2 19

[0054] Preferably, after the sending cache module receives the sending enable signal from the carrier sending module, it reads the earliest message cached by the sending cache module out of the cache, and calculates the difference between the time when the message is received from the protection device and the time when the message is received from the sending enable signal from the carrier sending module, as the cache delay of the message. If the cache delay exceeds the set time threshold, the message is an invalid message and is discarded. Otherwise, the message is a valid message.

[0055] Specifically, the time threshold set in this embodiment is 8 ms.

[0056] If there is no valid message in the cache when the sending buffer module receives the sending enable signal from the carrier sending module, a 32-byte empty message is sent to the carrier sending module;

[0057] When the sending buffer module sends a message, if the message is less than 32 bytes, it will be padded with 0 to make up 32 bytes before sending.

[0058] Preferably, the carrier sending module of the master MODEM module sends the carrier in each set period; the carrier sending module of the slave MODEM module sends the carrier only when the sending buffer module sends a valid message.

[0059] It should be noted that the carrier sending module of the MODEM module sends the carrier only when the sending buffer module sends a valid message. The channel delay from the carrier sending module receiving the valid message to sending the carrier is 1.6ms, and the jitter is less than 5us, which can ensure reliable communication of differential protection.

[0060] It should be noted that the carrier transmission module supports output amplitudes to adapt to different distance scenarios, and the bandwidth of the carrier converted by the carrier transmission module is adjusted at the center frequency according to the power line amplitude attenuation characteristics.

[0061] Preferably, the carrier receiving module determines whether the converted message is a valid message, specifically:

[0062] If the carrier is converted to the set message format and the fixed flag code is set, it is determined to be an invalid message converted from an idle carrier; otherwise, the message is subjected to length and 16-bit CRC check, and the message that passes the check is a valid message.

[0063] Preferably, the carrier receiving module calculates the time to be forwarded, adds it to the key information of the valid message, and caches the valid message, specifically:

[0064] Determine whether the cache delay of the valid message in another MODEM module is greater than the set delay time. If so, discard the valid message. Otherwise, calculate the set delay time minus the cache delay of the valid message in another MODEM module as the time to be forwarded, and add the key information of the valid message at this time into the information area of ​​the valid message.

[0065] Embodiment 2 of the present invention proposes a method for implementing optical fiber differential protection communication in a half-duplex channel, comprising:

[0066] When a protection device sends a message to another protection device, the MODEM module corresponding to the protection device sending the message receives the message sent by the protection device, verifies the message, and caches the content of the message and the key information of the message in the set message format for the correct message;

[0067] When it is necessary to send, the buffer delay of the message is calculated, the buffer delay of the message is added to the key information of the message, and the message is converted into a carrier and sent to another MODEM module; and the other MODEM module sends it to the protection device corresponding to another MODEM module;

[0068] When a protection device receives a message sent by another protection device, the MODEM module corresponding to the protection device receiving the message receives the carrier sent by the other MODEM module, converts it into a set message format, determines whether it is a valid message, calculates the time to be forwarded, adds key information of the valid message, and caches the valid message; when it is necessary to send the message to the protection device receiving the message, reads out and sends the valid message, and sends the valid message to the protection device receiving the message after encoding processing.

[0069] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0070] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0071] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0072] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be customized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A system for realizing optical fiber differential protection communication via a half-duplex channel, the system comprising a master MODEM module and a slave MODEM module, wherein both the master and slave MODEM modules comprise: The optical fiber receiving module, the sending buffer module, the carrier sending module, the carrier receiving module, the delay compensation module, the optical fiber sending module and the management module are characterized by: The two protection devices are connected to the master MODEM module and the slave MODEM module respectively; The input end of the optical fiber receiving module in the master and slave MODEM modules is connected to the corresponding protection device, receives the message sent by the protection device and verifies the message, sends the correct message to the sending buffer module, and the sending buffer module buffers the content of the message and the key information of the message in the set message format. When the sending buffer module receives the sending enable signal, it calculates the buffer delay of the message, adds the buffer delay of the message to the key information of the message, and then sends the message to the carrier sending module; the carrier sending module converts the message into a carrier; the output end of the carrier sending module is connected to the input end of the carrier receiving module of another MODEM module; The carrier receiving module receives the carrier sent by another MODEM module, converts it into a set message format, determines whether it is a valid message, calculates the time to be forwarded, adds the key information of the valid message, and caches the valid message; the delay compensation module receives the permission signal sent by the optical fiber sending module to the delay module, reads out and sends the valid message to the optical fiber sending module; the optical fiber sending module sends the valid message to the corresponding protection device after encoding; The management module is used to issue instructions to all other modules in the corresponding MODEM module and to collect statistics on the messages received and sent by all other modules.

2. A system for implementing optical fiber differential protection communication using a half-duplex channel according to claim 1, characterized in that: The optical fiber receiving module verifies the message, specifically: After the message is decoded by Manchester code and HDLC, a 16-bit CRC check is performed.

3. The system for implementing optical fiber differential protection communication using a half-duplex channel according to claim 1, characterized in that: The set message format is a fixed-size data frame format. The sending buffer module supports a data buffer of up to 8 frames. Each frame uses a fixed-size data area and information area. The data area stores the message content; the information area stores the key information of the message, including the frame length and the time information of the message being received.

4. A system for implementing optical fiber differential protection communication using a half-duplex channel according to claim 3, characterized in that: After the sending cache module receives the sending enable signal from the carrier sending module, it reads the earliest message cached by the sending cache module out of the cache, and calculates the difference between the time when the message is received from the protection device and the time when the sending enable signal from the carrier sending module is received, as the cache delay of the message. If the cache delay exceeds the set time threshold, the message is an invalid message and is discarded. Otherwise, the message is a valid message. If there is no valid message in the cache when the sending buffer module receives the sending enable signal from the carrier sending module, a 32-byte empty message is sent to the carrier sending module; When the sending buffer module sends a message, if the message is less than 32 bytes, it will be padded with 0 to make up 32 bytes before sending.

5. A system for implementing optical fiber differential protection communication using a half-duplex channel according to claim 4, characterized in that: The carrier sending module of the master MODEM module sends the carrier in each set period; the carrier sending module of the slave MODEM module sends the carrier only when the sending buffer module sends a valid message.

6. The system for implementing optical fiber differential protection communication using a half-duplex channel according to claim 5, characterized in that: The carrier receiving module determines whether the converted message is a valid message, specifically: If the carrier is converted to the set message format and the fixed flag code is set, it is determined to be an invalid message converted from an idle carrier; otherwise, the message is subjected to length and 16-bit CRC check, and the message that passes the check is a valid message.

7. A system for implementing optical fiber differential protection communication using a half-duplex channel according to claim 6, characterized in that: The carrier receiving module calculates the time to be forwarded and adds it to the key information of the valid message, and caches the valid message, specifically: Determine whether the cache delay of the valid message in another MODEM module is greater than the set delay time. If so, discard the valid message. Otherwise, calculate the set delay time minus the cache delay of the valid message in another MODEM module as the time to be forwarded, and add the key information of the valid message at this time into the information area of ​​the valid message.

8. The system for implementing optical fiber differential protection communication using a half-duplex channel according to claim 7, characterized in that: After the delay compensation module receives the permission signal sent by the optical fiber sending module, when reading out and sending a valid message to the optical fiber sending module, it first reads out the frame length and the time to be forwarded of the valid message buffered by the carrier receiving module; when the global time reaches the time to be forwarded, the message content of the valid message is read out.

9. The system for implementing optical fiber differential protection communication using a half-duplex channel according to claim 6, characterized in that: The optical fiber sending module sends the valid message to the protection device after encoding, specifically: the message content in the valid message is serialized, HDLC encoded, and Manchester code encoded.

10. A method for implementing optical fiber differential protection communication using a half-duplex channel of the system according to any one of claims 1 to 9, characterized in that: When a protection device sends a message to another protection device, the MODEM module corresponding to the protection device sending the message receives the message sent by the protection device, verifies the message, and caches the content of the message and the key information of the message in the set message format for the correct message; When it is necessary to send, the buffer delay of the message is calculated, the buffer delay of the message is added to the key information of the message, and the message is converted into a carrier and sent to another MODEM module; Sent by another MODEM module to the protection device corresponding to another MODEM module; When a protection device receives a message sent by another protection device, the MODEM module corresponding to the protection device receiving the message receives the carrier sent by the other MODEM module, converts it into a set message format, determines whether it is a valid message, calculates the time to be forwarded, adds key information of the valid message, and caches the valid message; when it is necessary to send the message to the protection device receiving the message, reads out and sends the valid message, and sends the valid message to the protection device receiving the message after encoding processing.

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