A new method to solve the distance limitation of RS232 remote serial port transmission

background:

The 35kV Weishan substation is a box-type integrated substation. The 35kV and 10kV equipment protection devices and remote control device WYD-801 are installed in the box transformer. The communication equipment room of the substation is equipped with communication equipment (intelligent PCM SDH optical transceiver), which is responsible for receiving the remote control device WYD 801 sends data and sends it to the dispatching end. The box-type transformer is more than 60 meters away from the dispatching communication room. The remote control device WYD-801 remote digital serial port is RS-232. According to the book “Principles and Applications of Comprehensive Automation in Substations” Chapter 2 RS-232 Remote Serial Port Electrical Characteristics We know: RS-232 uses a single-ended drive and single-ended receiving circuit, its data transmission rate is limited to 20kbps, and the theoretical transmission distance is limited to 15 meters (“Integrated Automation of Substations” “Principles and Applications” book), if ordinary audio cables are used as telecontrol transmission channels, the data attenuation will be very large, and the channel bit error rate will be very high (see the figure below). Obviously, this transmission method cannot meet the requirements. .

Propose a plan and demonstrate it

In view of the current situation of the telecontrol channel in the Weishan substation, as well as the technical characteristics of Rs232, RS-485 and RS-422 serial communication, after careful analysis and research, the following three solutions are proposed:

(1) Install a modem on the WYD-801 digital serial port of the box-type remote control device, convert the digital signal into an analog signal through the modem, transmit it to the intelligent PCM SDH optical terminal of the optical transmission equipment in the communication room through the audio cable, and finally upload and schedule through the optical fiber channel (see Attachment 2). Demonstration: This solution converts digital signals into analog signal transmission, which solves the bottleneck of digital signal transmission limited by distance. However, it requires the installation of a modem, which increases the cost, and analog signal transmission is greatly affected by electromagnetic fields and has poor anti-interference ability. The channel bit error rate will affect the accuracy of data transmission.

(2) Install a 2-meter-high cabinet and PCM subframe in the box transformer, lay 60 meters of 8-core coaxial cable between the communication computer room and the box transformer, and complete the connection of the 2M line of the digital distribution frame between the communication computer room and the box transformer. , the WYD-801 digital signal of the remote control device is transmitted to the SDH optical transceiver in the communication room through the 2M data line of the PCM equipment, and finally uploaded for scheduling through the optical fiber channel (see attached figure 3). Argument: This solution cleverly uses 2M lines to transmit telecontrol signals. The digital signal has strong anti-interference ability and low signal attenuation. However, due to the limited space within the box-type transformer, cabinets and PCM equipment cannot be installed.

(3) Install an RS-232/422/485 serial port converter at both ends of the box-type remote control device WYD801 and the optical transmission equipment in the communication room to achieve remote communication. (Since the dispatching end needs to issue remote control and remote adjustment commands, RS-232/422 four-wire wiring is used. The wiring diagram is as follows). Demonstration: This solution converts the digital RS-232 signal into RS422 transmission by installing an RS-232/485/422 serial port converter at the RS-232 digital serial port of the WYD 801 remote control device of the box-type transformer. Since the RS-485/422 data The transmission adopts differential transmission, also called balanced transmission, with a maximum transmission distance of 2 kilometers and a maximum transmission rate of toM/s. The converter is small in size and low in cost, making it very suitable for on-site requirements.

(4) Conclusion: Option 1: On-site remote data transmission can be realized, but because the transmission channel is an analog channel, data transmission is greatly affected by the environment and has poor anti-interference ability, so it can be used as a backup channel; Option 2: Due to the location inside the box transformer It is limited and cannot be realized, but it can be the best choice when there are many telecontrol and audio signal transfer links between factories. Option 3: Use a digital serial port converter to achieve telecontrol transmission, with strong data anti-interference ability and channel error. rate is low. This solution meets the requirements. After contacting communication manufacturers, we finally chose the passive serial converter RPEO1, a product of Wuhan Ruifeng Communication Technology Co., Ltd.

Summarize:

At present, the CBZ-8000 integrated automation system of the 35kV Weishan Transformer is running normally and stably. By installing the serial port converter, the bit error rate of the remote control channel is zero, the telemetry data is accurate, the remote signaling is reflected in real time, and the dispatcher issues remote control and remote adjustment commands. , can be executed correctly and fully meet the “Practical Acceptance Rules for County-level Power Grid Dispatching Automation System”, laying a solid foundation for dispatchers to monitor the power grid in real time and allocate loads reasonably.