Differences and applications of communication protocols between CDT, Modbus, 103, 101, 104, DL/T645, and IEC61850

Differences and applications of communication protocols between CDT, Modbus, 103, 101, 104, DL/T645, and IEC61850

Limitations: Most photovoltaic power systems use wired communication, including serial ports, network ports, and optical ports. Wireless communication is sometimes used for distributed photovoltaic power generation. There are also many communication protocol specifications, including CDT, Modbus, 103, 101, 104, DL/T645, and IEC61850 communication protocols. Below is a brief introduction to the differences between them.

1、 Serial communication

Currently, many people still frequently use serial communication. Due to the relatively stable serial communication, shielded wires have anti-interference effects. And it was applied early in China, with high recognition. Common serial communication rules include CDT rules and DISA rules (upgraded version of CDT rules), modbus protocol serial port, 103 protocol, 101 protocol scheduling, DL/T645, etc.

1) The CDT protocol is an earlier application of the protocol. For broadcast type messages, the sub station will play the message to the communication management machine based on the communication line, and then the communication management machine will convert the regulation into a message that can be recognized by the backend upper computer, analyze it, and display it on the upper computer. The DISA protocol is an evolved version of the CDT protocol. This regulation includes monitoring points, and the number of remote information points will exceed the original CDT protocol. There is no significant difference in message format. The wiring method is RS-232. There are three lines: receiving, sending, and grounding. Due to the short communication distance, it is about 10 meters. Currently, the market share is not very high due to the limited usage. Only some small current grounding devices and DC screens are still using this communication method.

2) Modbus communication protocol is a common communication protocol widely used in industry. It is also used for shielded twisted pair cables, namely RS-485. The communication distance of this communication method is relatively long. In theory, it can reach over 1000 meters. Of course, this also depends on the communication interface capability of the manufacturer’s communication management machine. At present, some manufacturers also retain this communication method for maintenance. For example, in the new energy applications under Lingqi Technology, there are photovoltaic box transformer control and wind power box transformer control. This communication method is relatively simple, and question and answer messages are also easy to understand. Easy to identify issues during device debugging.

3) 103 serial communication is commonly used for microcomputer protection. Such regulations can send the internal points protected by microcomputers without error, including total movement and displacement data. As a station maintenance equipment, the 103 communication function is a prerequisite.

4) 101 serial communication is a scheduling communication regulation. On site wiring is sometimes a four wire system, and sometimes a three wire system. This type of regulation is currently used for ground adjustments. Transfer data to the ground adjustment center based on the data network cabinet.

5) The DL/T645 protocol is generally used for electricity meters, and the full name specified in 645 should be “DL/T645-1997 Communication Protocol for Multi functional Electricity Meters in the Power Industry of the People’s Republic of China.”.

2、 Network communication

At present, network communication is also widely used. It has a fast transmission speed. At present, common regulations include 104 protocol, 103 protocol, modbus TCP protocol, etc. Below will be a brief introduction.

1) The 104 protocol is currently a common protocol for remote mobility and centralized control. The amount of information specified in this regulation can generally meet the actual needs of the site and is usually applied in provincial dispatching. However, some adjustments will also prioritize the 104 protocol, mainly considering its stable and easy to maintain characteristics.

2) The format of communication messages on the 103 network port is not significantly different from that on the serial port 103, but there are significant differences in communication settings. It is also a communication protocol for microcomputer protection.

3) The modbus TCP protocol is the modbus protocol for network ports and is also a question and answer format. It is always used for communication with third-party devices or centralized control stations, and is currently not widely used in power systems.

3、 Optical communication

The key to optical communication should be the smart grid on the current power supply system, which applies the full name of the 61850 Treaty and IEC61850 series standards: Communication Networks and Systems in Substations. It regulates the communication behavior of intelligent electronic devices (IEDs) within distribution stations and the communication behavior between related series regulations.