The DC power supply section of a power system consists of battery banks, charging equipment, DC power panels, and other equipment. Its functions are: under normal conditions, to provide DC power for closing circuit breakers in the substation; and during faults, to provide working DC power for relay protection and automatic devices, circuit breaker tripping and closing, carrier communication, and plant machinery driven by DC motors when power to the plant or substation is interrupted. Its proper functioning directly affects the safe and reliable operation of the power system. In the past, each substation in the power system was staffed, allowing for regular inspections of the DC equipment's operating status, thus enabling timely detection and handling of any abnormalities and ensuring the safe and stable operation of the substation. Currently, the power system is promoting unmanned substations. Although the dispatch center can obtain real-time information on the substation's operating status through remote control channels, it can only obtain a limited amount of important information regarding the DC section (including: remote signaling quantities—charger AC power supply faults, charger faults, DC insulation grounding, DC power supply voltage anomalies; remote measurement quantities—control bus voltage). It cannot reflect detailed information about the operation of the DC system, especially it cannot detect the initial signs of abnormal operation. It only sends a dispatch alert when prolonged abnormal operation develops into a fault, by which time the incident has already escalated. If abnormalities can be detected and addressed promptly when they first appear, the escalation of the problem can be prevented. Therefore, regular inspections by equipment maintenance personnel are necessary. Furthermore, the control of DC equipment operation is also performed on-site by maintenance personnel. With many substations and a limited number of maintenance personnel, it is clearly impossible to guarantee timely and sufficient completion of tasks. In this context, the DC monitoring system has emerged. Its main function is to upload information about the DC equipment from each substation to the monitoring center for querying, while the monitoring center can also send control commands to each station. In this way, maintenance personnel can not only remotely monitor the DC equipment from the monitoring center but also promptly detect and address abnormal operating conditions, preventing them from developing into accidents. Therefore, the establishment of a DC monitoring system can save manpower and resources and improve work efficiency. **1 Channel Selection** Currently, various information transmitted from substations to the dispatch center, such as telemetry, telesignaling, remote control, main equipment status, and alarm information, is transmitted through the remote control channel. This information has high real-time requirements, and it's undesirable for other information to occupy the channel and cause congestion, affecting the normal operation of the dispatch center. Therefore, the operating information of DC equipment must be transmitted remotely through another channel. Currently, in addition to the remote control channel, substations also have a telephone channel. This channel is generally used by staff during on-site work and by other auxiliary systems such as safety alarm systems when necessary. This channel is usually idle, but it is essential, so it can be used as the information channel for the DC monitoring system. The DC monitoring system has a small amount of data, and the channel occupancy time is short when transmitting. Thus, the channel can be used during work, occupying the channel, and then disconnected after work, sharing the channel with other systems in a time-sharing manner, thereby ensuring the normal operation of each system. **2 System Composition** The system structure diagram is shown in Figure 1. The monitoring center computer is connected to the telephone network via a modem. The monitor is also connected to the telephone network via a modem. Both modems can call each other, establishing a communication link through their respective modems and the telephone network to exchange information. In this way, the monitoring center computer can use this communication link to collect information from each substation's monitors, send control commands, and each substation's monitors can also report daily scheduled operating data and abnormal situation information to the center. The system consists of three parts: the monitors are the front-end system, responsible for collecting equipment data, controlling operating status, and transmitting information; the monitoring center is the back-end system, running on a PC, responsible for sending commands to all substation monitors, receiving their operating data, and processing and analyzing the data; data communication between the two relies on modems and the telephone network. The monitoring center and monitors form a one-to-many system. 3 Monitor Design 3.1 Monitor Principle The monitor is a system installed in each substation. It collects operating status information from each DC device, controls it, and transmits the data to the monitoring center and other monitoring units. The monitor is designed using an industrial control computer. Its I/O ports are used for input and output. It can directly acquire measured quantities, status quantities, and battery insulation status information from DC equipment. It can also control and regulate DC equipment, such as the on/off operation of the charger, changes in equalization and float charging, changes in equalization and float charging voltage, and the opening and closing of feeders. On the other hand, the microcomputer controller sends remote control signals to the RTU or dispatch center via RS232 or modem, and transmits the operating information of all DC equipment to the monitoring center where the equipment maintenance personnel are located via the modem and telephone network. 3.2 Monitor Software Design The monitor software consists of four modules: a communication module, a data transceiver module, an I/O module, and a data processing module. The communication module prepares for communication for data transmission, including turning the modem on and off and automatic dialing functions. The software is set to turn the modem on and off at regular intervals, which allows this system to share the telephone channel with other systems such as alarm systems. Automatic dialing automatically connects to the monitoring center's modem when an abnormal event occurs in the DC equipment, sending the corresponding alarm information. The data transceiver module is mainly responsible for data transmission and reception after the communication link is established. The transmitted data includes: the current operating information of each DC device; historical data stored in this monitor for a fixed time within 24 hours; and all alarm information within 24 hours. The received data includes control and adjustment commands from the monitoring center. The I/O module functions include: providing the monitor's human-machine interface, and the monitor's acquisition and control of quantities from each DC device. The data processing module is the core module of the monitor. On one hand, it processes the data obtained by the I/O module and stores the daily data in the database according to the set time intervals, ready for the data transceiver module to send to the monitoring center. This data is updated daily. On the other hand, it analyzes the control commands received by the transceiver module and provides control information to the I/O module. [b]4 Monitoring Center Design[/b] The monitoring center is a microcomputer on which the monitoring center background software runs. The monitoring center software mainly includes four parts: a communication module, a database generation module, a main control module, and a report printing module. The communication module functions similarly to the monitor's communication module, establishing a communication link by connecting to the substation's monitor modem and sending control commands. It can also be connected to and receive information uploaded by other devices. Developed using Visual Basic 5.0, this module only needs to establish a communication link by connecting to the modem. The specific data transmitted is irrelevant and handled by the main control software. The data processing module serves two purposes: first, it creates a database of information for each substation's DC equipment; second, it organizes and stores the daily data collected from each substation into a historical database of all substation DC equipment. Users can flexibly create databases for each substation and all its DC equipment according to their needs, and maintain all substation information automatically after maintenance. This system offers high flexibility and ease of operation. Furthermore, each substation monitor regularly uploads its daily data to the monitoring center, which then stores it in its respective database based on the substation name, forming a historical database for use by the report printing system. The main control software provides a human-machine interface based on the Windows 95 operating system, allowing users to operate the on-screen graphics using a mouse and keyboard. By simply clicking on the corresponding graphic element of the device component with the mouse, the device can be queried and controlled. The device parameters can also be input via the keyboard to remotely adjust the device's operating parameters. Maintenance personnel can query and control the equipment within the operating station using the mouse and keyboard. Once the communication module establishes a communication link, it can open the data information sent from afar, display it on the screen, and then process this data through the data processing module. It also sends the operator's control commands to the remote location in the form of data packets. This is the core of the system. The report printing module, according to work needs, queries the historical database stored in the data processing module to generate daily, monthly, and other reports, as well as corresponding data curves for analysis and querying. [b]5 Conclusion[/b] The DC monitoring system was jointly developed by Shenzhen Power Supply Bureau and Shenzhen Aote Xun Company and is currently in operation. Through this system, DC equipment maintenance personnel can remotely monitor the operating status of DC equipment in each substation from the monitoring center, eliminating the need for on-site scheduled inspections of each substation. Especially when DC equipment malfunctions, operation and maintenance personnel can receive alarm signals promptly and handle them in a timely manner. In summary, the operation of the DC monitoring system has reduced workload, improved work efficiency, and achieved the goal of reducing manpower and increasing efficiency.