Object-oriented substation automation systems distribute functional units across the production site to collect information. These functional units are microprocessor-equipped measurement and control devices, each corresponding to a specific piece of on-site production equipment, and possess independent information storage and processing capabilities. This improves the automation level of the substation, alleviates the information processing pressure on the upper-level management system, and provides abundant reference information for inspection and on-site commissioning personnel. [b]1 Concept of Local Functional Units[/b] 1.1 Object-Oriented Substation Integrated Automation The substation is the source of all data for the power grid and its main control point. Substation integrated automation can be considered from two perspectives: function-oriented and object-oriented. Traditional integrated automation schemes tend towards the former, where secondary equipment design is based on function, dividing it into data acquisition units, control units, remote communication units, etc. The advantages of this method are ease of maintenance and management, and low hardware costs; the disadvantages are complex secondary wiring and a wide range of potential hazards from accidents. With the development of large-scale integrated circuit manufacturing processes, the cost of microcomputer devices has decreased, making it possible to deploy microcomputer devices to the production site, thus leading to a layered substation integrated automation structure. This structural design not only reduces secondary wiring and disperses the destructiveness of secondary equipment failures, but also facilitates on-site debugging by maintenance personnel. Currently, most imported equipment adopts this distributed construction method, and many domestic production and research units are also committed to this work. Object-oriented design starts from the perspective of objects and maps secondary equipment to primary equipment one by one. However, this concept is not simply equivalent to distributing intelligent devices (relay protection devices, smart meters, programmable logic controllers, etc.) on the field. It is a brand-new idea that breaks the current professional division of labor, that is, closely integrating the design of secondary equipment with the design of primary equipment. Taking switch cabinet as an example, each TA should use intelligent measurement units to directly output digitized sampling data; the control circuit of each phase switch should be directly integrated into the operating mechanism of the switch; the position sensor of each knife switch has intelligent information communication to facilitate interlocking. Each switch cabinet has an integrated controller to collect information from each sensor and coordinate control to complete protection, measurement and control functions [1]. 1.2 Concept of local functional unit Due to the current professional division of labor, we cannot yet achieve object-oriented design in a completely meaningful sense. However, unlike the general measurement and control unit, the local functional unit mentioned here has an object-oriented nature, that is, it is deployed to the field and corresponds one-to-one with the measurement and control object, integrating protection, measurement and control, and recording more information about primary equipment. With its help, we can obtain the current working condition of a specific measurement and control object, the action before and after the fault, the switch status and the degree of loss, etc. In addition, with the help of the communication network, we can also realize remote or local setting modification, remote or local control and other functions. 2 Design of monitoring program 2.1 Tasks of local functional unit (1) Reflect real-time status: voltage, current, power, power factor, functional unit status (normal or debugging status), object working status (normal or fault, transformer oil temperature, etc.). (2) Record historical data: fault report, operation record, device error report, fault waveform, maintenance diagnosis (diagnosis of primary equipment such as switches and self-test of the device itself). (3) On-site modification of protection settings, on-site control of switches. (4) Flexible communication capability, with optional RS-422 and RS-485 serial data interfaces, which can remotely transmit data and real-time information in the device through the corresponding communication management unit. Or, the device can communicate with the PC without networking through RS-232. 2.2 Information stored and processed by local functional units Since the primary equipment corresponding to each functional unit is not completely the same, the information to be recorded is also different, but the database structure is the same to ensure the inheritability of the monitoring program. (1) Real-time power of the monitored and controlled object, such as: current, voltage, active power, reactive power, etc. A buffer is opened in RAM for communication and display. (2) Three sets of protection setting backups are stored in EEPROM, and a set of protection setting buffers is also opened in RAM for modifying settings and communication. (3) 16 fault information entries are stored in EEPROM, including: protection operation status, operation value and setting value, operation time, operation category, maximum trip current, maximum trip current after reclosing, time from fault detection to trip command, and time from fault detection to tripping. 16 operation information, including: operation permission, operation content, operation time. 16 error information, including: error type, error time. A corresponding buffer is opened in RAM for refresh and communication. (4) Record the sampling data for 5 cycles after the fault occurrence time, i.e. fault recording. 2.3 Structure of the monitoring program The tasks of the local functional unit are divided into 8 main functional modules. According to the number of tasks, sub-modules are further divided. Figure 1 shows the modular structure of the monitoring program. Figure 1 Modular structure of the monitoring program To ensure the real-time performance of the measurement, the monitoring program stops sampling and measurement calculation when responding to key presses and displaying information. The specific implementation method is: sampling is placed in the interrupt program, and measurement calculation is placed in the loop part of the main program. When the user presses the key, it will switch to the corresponding processing and record the path traversed by the program. Then it will continue to perform measurement calculations uninterruptedly until the next key press occurs. The monitoring program can continue to process the previous response according to the path record. **3. Information Display Method of Functional Units** When installing functional units locally, it is essential to consider whether the device can withstand harsh on-site conditions. Currently, most functional unit monitoring interfaces use LCD displays. LCDs can display Chinese characters, providing relatively intuitive information prompts, but they also suffer from poor high-temperature resistance and low visibility. Using large digital tubes can overcome these shortcomings, but digital tubes can only display numbers and a limited number of English letters, resulting in a more abstract expression. However, the information displayed by locally installed functional units is primarily for inspection and on-site debugging, so visibility and tolerance to harsh conditions should be prioritized. Detailed data display and analysis can be performed on the upper-level management unit or communicated with a portable device via an RS-232 serial port. Based on the above functional division and considering on-site requirements (such as the size limitations of most functional units built into switch cabinets, and the limited number of digital tubes and keyboards), we designed the panel shown in Figure 2. The panel is labeled with each part. Figure 2 shows the device panel information display area, which consists of six large digital tubes. The two leftmost tubes are generally used to display prompts, while the remaining tubes are used to display numbers or, in conjunction with the first two digits, to display longer prompts. The function lights act as a menu, allowing users to select functions by pressing function keys. The selected function light flashes, and pressing the confirmation key keeps the light on, indicating that the user has entered that function. Simultaneously, a corresponding prompt appears in the information display area. The unit light, in conjunction with the numbers in the information display area, displays the electricity level and its unit. Both the function lights and unit lights separate the eight digits of the digital tube, with each digit corresponding to one light. This design maximizes hardware resources and makes the hardware layout more compact. 3.1 Information Query: Setting value management and information query involve a lot of content, requiring separate display. The following uses setting value management as an example to explain in detail how to use digital tubes to query information. When the user switches to the "setting value" function using the function keys and presses the confirmation key, the "setting value" function light remains on. In this state, keyboard operations and displayed information are all related to setting values. The "+" and "-" keys on the keyboard are used to search for zones, and the "↑" and "↓" keys are used to search for items. Taking the capacitor local function unit as an example, it needs to be configured with 7 different protections: delayed current instantaneous trip, overcurrent, overvoltage, undervoltage, unbalanced voltage, unbalanced current, and overload. Therefore, there are 7 different settings. To facilitate user queries, these 7 sets of settings are divided into 7 zones, with items within each zone. Taking searching for the overcurrent protection setting in the second zone as an example: After entering the setting management, the user presses the "+" key twice to enter the second zone and a prompt message is displayed. Pressing the "↓" key displays the first setting, and continuing to press the "↓" key will display each setting item sequentially until the last item. Because it is divided into zones and indexed by numbers, although only one piece of information can be displayed at a time, searching is quite convenient. The disadvantage is that users must use the setting table when modifying settings. 3.2 Modifying Numbers Whether modifying settings or changing passwords, both involve numerical input. Here we designed a convenient and quick modification method: The last four digits of the LED display show four significant digits. The "↓" and "↑" keys are used to shift the value; the digit that is currently being shifted flashes, indicating the current digit. The "+" and "-" keys are used to change the value, with the step size automatically adjusted. For example, to change from 10.00 to 700.0, use the "↑" key to move to the highest digit, then press the "+" key. Starting from 0, the value increases in steps of 10. When it reaches 100, the decimal point is automatically adjusted to 100.0 (ensuring four significant digits). If you don't shift, continuing to press the "+" key will increase the value in steps of 100, meaning the step size is always automatically adjusted to the order of magnitude of the currently flashing digit. When the number exceeds 1000, the unit LED automatically switches to the kA or kV level, and the step size adjusts accordingly. [b]4 Conclusion[/b] The monitoring program of the functional unit using digital tube display introduced in this paper is designed based on the object-oriented concept. In practical applications, it mainly has the following characteristics: (1) High-precision measurement and clear display. The measurement accuracy reaches 0.5 level, which makes it able to replace conventional measuring instruments. In order to facilitate the intuitive inspection of operators, a large digital tube is used in the design to complete the output display of information in the device, which has strong visibility. (2) Convenient human-machine interface and operation debugging. In the design of the functional unit, considering the needs of on-site operation, various information prompts are designed to meet the needs of local operation, which facilitates the information processing of human-machine interaction. (3) Selectable communication and information processing modes. In order to meet the needs of the development of distributed microcomputer automation in power systems, the functional unit is designed with selectable RS-422 and RS-485 serial data interfaces. Through the communication management unit that cooperates with this series of devices, the remote transmission of data and real-time information in the device can be completed. For independent units without network connectivity, the device also provides a universal RS-232 interface. Users can use this interface and debugging and communication software developed in the WINDOWS 95 environment to access the device's operating information without network connectivity. (4) Complete fault waveform information. (5) Detailed operation and operation records. The main circuit of the functional unit is equipped with a non-power-off clock chip to provide accurate timing for various information recordings. During operation, the protection setting, debugging and operation status are automatically recorded. This information includes time information and is saved even when power is off, providing detailed operation records for the normal operation of the device and post-event analysis. During operation, the current change of the switch during the tripping process is recorded, especially the maximum current during the arc extinguishing process of the switch, which facilitates the damage analysis of the switch contacts and provides a basis for the maintenance and replacement of the switch. **References** 1. Tao Xiaonong. Communication technology solutions in distributed substation monitoring systems. Automation of Electric Power Systems, 1998, 22(4): 51-54. 2. Huang Taigui. Application of intelligent electronic equipment in substation integrated automation. Automation of Electric Power Systems, 1998, 22(3): 54-55. Editor: He Shiping