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At present, power systems mainly use wired communication through serial ports, network ports, and optical ports. Distributed photovoltaics sometimes also use wireless communications. Because serial port communication has the characteristics of stability, anti-interference, early use, and high recognition, serial port communication is often used in power systems. Communication protocols such as CDT protocol, DISA protocol (upgraded version of CDT protocol), Modbus protocol, 103 protocol, dispatching 101 protocol, DL/T645 and other communication protocols are relatively common in power systems. Changhui briefly introduces them in this article. 1. CDT protocol The CDT protocol is an earlier protocol. The message type is broadcast. The substation will broadcast the message to the communication management machine through the communication line. The communication management machine will then convert the protocol into a message that can be recognized by the background host computer, thereby parsing it and displaying it on the host computer. The DISA protocol is a derivative of the CDT protocol. Its protocol contains telemetry points, and the number of remote signaling points is greater than that of the original CDT protocol. There is no obvious difference in message format. The wiring method is RS232. That is, the three lines of receiving, sending and ground. Since the communication distance is short, it is about 10 meters. It is rarely used nowadays. Today, some small current grounding line selection equipment and DC panels still retain this communication method on the market. Key points of CDT protocol ① The source address and destination address are set to 1. ②The frequency forwarding sequence number setting starts from an even number, usually 2 points are placed in an information word, the function code is 0x8A, and the BCD code is sent. ③The forwarded telemetry value is required to be transmitted once, and the coefficient value must be configured. (Engineering conversion or scaling) ④Forward telemetry values with quality description. Set overflow flag: If the rated value is less than 2047, it is set to the rated value, if it is greater than 2047, it is set to 2047, and the voltage limit is set to 1.2 times the rated value. Since the maximum code value sent by CDT is -2048~2047, when the maximum value is greater than 2047, the transmission must be scaled down. The total telemetry can be calculated and uploaded ⑤ The telemetry forwarding sequence can be set: ABA ABA ABC ABA ABA ABC ABA ABA ABC D1 D2 (for example) ⑥Telemetry is divided into important telemetry, secondary telemetry and general telemetry. YCA32 points; YCB32 points; YCC remaining points, there are 128 function codes allocated for telemetry, and the maximum number of transmissions is 256. There are 16 function codes allocated by D1 remote signaling, and the maximum number of transmissions is 512. ⑦ Only one SOE is sent to each E frame. ⑧The North China network adjustment requires telecontrol to send data through dual channels to ensure that the data on the main and backup channels are completely consistent. (Dual machine parallel or single machine dual channel) ⑨The total accident signal is placed first in remote signaling, that is, YX1 ； It is "1" when there is an accident and "0" when there is no accident. Total plus telemetry upload. Prioritization order and transmission time requirements for uplink information during CDT communication ◆ Substation clock return information for time synchronization is inserted and transmitted ◆ Displacement remote signaling and substation working status change information are inserted and transmitted, and are required to be sent to the master station within 1s ◆ Return check information of remote control and lifting commands is inserted and transmitted ◆ Important telemetry is arranged to be transmitted in the A frame, and the cycle time is not more than 3s ◆ Secondary telemetry is arranged to be transmitted in the B frame, and the cycle time is generally not more than 6s ◆ Generally, telemetry is scheduled to be transmitted in the C frame, and the cycle time is generally not greater than 20s. ◆ Remote signaling status information, including substation working status information, is scheduled to be transmitted regularly in the D1 frame. ◆ The power pulse count value is scheduled to be transmitted regularly in the D2 frame. ◆ Event sequence records are scheduled to be transmitted in the E frame in frame insertion mode. ◆ The priority of downlink (master station to slave station) commands is arranged as follows.: ◆ Summon the substation clock, set the substation clock correction value, and set the substation clock ◆ Remote control selection, execution, and cancellation commands, lifting and lowering selection, execution, and cancellation commands, setting commands ◆ Broadcast command ◆ Reset command ◆ The remote signaling status and power pulse count value transmitted by the D frame are slowly changing quantities, and are transmitted cyclically in a few minutes to dozens of minutes. ◆ The event sequence record transmitted by the E frame is a random quantity, and the same event sequence record should be transmitted repeatedly within three E frames. 2. Modbus communication Modbus communication is a common communication and is widely used. Also used is shielded twisted pair, namely RS485. This communication method has a relatively long communication distance. Theoretically, it can reach more than 1,000 meters. Of course, this also depends on the capability of the communication interface of the manufacturer's communication management machine. At present, some manufacturers still retain this communication method. Such as photovoltaic box transformer measurement and control for new energy use, wind power box transformer measurement and control, etc. This communication method is relatively simple and belongs to the question-and-answer format. The message is also relatively easy to understand. It is convenient to find problems during debugging. Changhui Instrument Network has introduced the RS485 communication protocol in detail in "RS485 Maximum Communication Distance and RS485 Interface Definition", you can go to learn more. 3. 103 serial port communication 103 serial port communication is generally used for microcomputer protection. Currently, manufacturers such as Nanjing Panneng Electric Power Technology Co., Ltd. and Xu Ji Electric Co., Ltd. use the 103 protocol for their own protection and communication with the host computer in the station. This protocol can transmit the internal points protected by the microcomputer without any error, including total stroke and displacement data. As an in-site protection device, it is a basic prerequisite to have 103 communication functions. 4. 101 communication 101 communication is used as a scheduling communication protocol. The wiring in the field is sometimes a four-wire system, sometimes a three-wire system. This convention is currently used in geo-tuning. Transmit the data to the ground control center through the data network cabinet. 5. DL/T645 protocol DL/T645 protocol is a communication protocol developed for electric meter communication. There are two main versions.: DL/T645-1997 and DL/T645-2007, DL/T645 protocol is usually used on electricity meters. There are still many differences between DL/T645-1997 and DL/T645-2007. Changhui Instruments analyzed the differences between DL/T645-1997 and DL/T645-2007 based on the practical application of A-phase voltage and A-phase current data communication of a certain brand of electricity meter.: ①Phase A voltage ◆ DL/T645-2007 protocol sends original message: 6861 01 00 00 00 00 68 11 04 33 34 34 35 17 16 minus 33H processed message: 68 61 01 00 00 00 00 68 11 04 00 01 01 02 17 16 Function: The master station requests to read the A-phase voltage command address field of the electric energy meter.: A0-A5: 610100000000H control code: C=11H, indicating that the master station requests to read the energy meter data identification code: DI3DI2DI1DI0=02010100H, indicating phase A voltage, occupying 4 bytes of data field length: L=04H Receive original message: 68 6101 00 00 00 00 68 91 06 33 34 34 35 34 43 10 16 minus 33H processed message: 68 61 01 00 00 00 00 68 91 06 00 01 01 02 01 10 10 16 Address field: A0-A5: 610100000000H control code: C=91H identification code: DI3DI2DI1DI0=02010100H, which represents the A-phase voltage and occupies 4 bytes. The length of the data field is: L=04H+02H=06H Phase A voltage is: 100.1V, occupies 2 bytes ◆ DL/T645-1997 protocol sends original message: 6803 00 00 00 00 00 68 01 02 44 E9 03 16 minus 33H processed message: 68 03 00 00 00 00 00 68 01 02 11 B6 03 16 address field: 030000000000 Function: The master station requests to read the A-phase voltage command control code of the electric energy meter.: C=01H, indicating that the master station requests to read the energy meter data identification code: DI1DI0=B611H, indicates phase A voltage, occupies 2 bytes of data field length: L=02H Receive original message: 68 0300 00 00 00 00 68 81 04 44 E9 33 34 EC 16 minus 33H processed message: 68 03 00 00 00 00 00 68 81 04 11 B6 00 01 EC 16 address domain: 030000000000H control code: C=81H identification code: DI1DI0=B611H, which represents the A-phase voltage and occupies 2 bytes. The data field length is: L=02H+02H=04H Phase A voltage is: 0100V, occupies 2 bytes ②A phase current ◆ DL/T645-2007 protocol sends original message: 6861 01 00 00 00 00 68 11 04 33 34 35 35 18 16 minus 33H processed message: 68 61 01 00 00 00 00 68 11 04 00 01 02 02 18 16 Function: The master station requests to read the A-phase current command control code of the electric energy meter.: C=01H, indicates that the master station requests to read the energy meter data identification code: DI3DI2DI1DI0=02020100H, indicating the A-phase current, occupying 4 bytes of data field length: L=04H Receive original message: 6861 01 00 00 00 00 68 91 07 33 34 35 35 CC 7C 33 16 16 minus 33H processed message: 68 61 01 00 00 00 00 68 91 07 00 01 02 02 99 49 00 1616 Control code: C=91H identification code: DI3DI2DI1DI0=02020100H, indicates phase A current, occupying 4 bytes of data field length: L=04H+03H=07H Phase A current is: 004.999A, occupies 3 bytes ◆DL/T645-1997 protocol to send original message: 68 03 00 0000 00 00 68 01 02 54 E9 13 16 minus 33H processed message: 68 03 00 00 00 00 00 68 01 02 21 B6 13 16 Function: The master station requests to read the A-phase current command control code of the electric energy meter.: C=01H, indicates that the master station requests to read the energy meter data identification code: DI1DI0=B621H, indicates phase A current, occupies 2 bytes of data field length: L=02H Receive original message: 6803 00 00 00 00 00 68 81 04 54 E9 CC 37 98 16 minus 33H processed message: 68 03 00 00 00 00 00 68 81 04 21 B6 99 04 98 16 Control code: C=81H identification code: DI1DI0=B621H, indicates phase A current, occupies 2 bytes of data field length: L=02H+02H=04H Phase A current is: 04.99A, occupies 2 bytes. Through the above introduction, I believe that everyone has a general understanding of the CDT protocol, DISA protocol, Modbus protocol, 103 protocol, dispatch 101 protocol, and DL/T645 protocol. Proficient use of these communication protocols must be combined with on-site application practice to master the essence. This is essential knowledge for debugging power instruments, power devices, and equipment. source: thermostat http://blog.sina.com.cn/u/6430376461