The CSC2000 substation automation system is a new generation substation automation system developed and designed by Beijing Hardway Sifang Protection and Control Equipment Co., Ltd. This system adopts a hierarchical, distributed design approach and utilizes LONWORKS fieldbus technology, creating a bus local area network within the system. It has been widely used in substations of different voltage levels from 35 kV to 220 kV and has received positive feedback from users. As a crucial component of this system, the master remote control station (MASTER) breaks through the limitations of traditional RTU designs. It fully utilizes the LONWORKS network within the substation to communicate with protection units and complete the four remote functions (remote control, remote monitoring, and remote operation). Compared to traditional RTUs, the MASTER offers many advantages, such as the number of remote control points not being limited by hardware conditions like the number of terminal blocks, expandable capacity, significantly simplified secondary wiring, and a high performance-price ratio. The 8890 protocol was originally developed by the American company EMPROS for communication between the dispatching system and RTUs. Later, this company was acquired by Siemens and became Siemens AG, but it maintained its original product structure and system. Therefore, the systems and practices of Siemens AG and Siemens AG for the same type of product differ significantly. Fujian and Zhejiang provinces in my country have introduced the Siemens dispatching system from the United States. Communication between substations above 220 kV and the provincial dispatch center uses Siemens RTUs via the 8890 protocol. Heilongjiang Province has introduced four such dispatching systems for its municipal dispatching system. The municipal dispatching system requires communication with many substations, and the remote control equipment is complex. Therefore, it is neither economically nor technically feasible to completely switch to Siemens RTUs. This raises the question of how domestic remote control equipment can interface with foreign dispatching systems. The 8890 protocol differs significantly from commonly used domestic remote control protocols such as 1801, N4F, and DNP3, possessing many unique characteristics. This increases the difficulty of interfacing domestic equipment with it. Because it has not been widely used domestically before, domestic professionals are not very familiar with the 8890 protocol. This article provides a brief introduction to this protocol, compares it with other question-and-answer protocols, and offers corresponding commentary. Finally, based on the author's experience in successfully interfaced with the 8890 protocol, the implementation scheme of the CSC2000 automation system interface with the 8890 remote control protocol is introduced for reference by domestic peers. [b]1 CSC2000 System Remote Control Master Station [/b] 1.1 System Structure Figure 1 is a simplified diagram of the CSC2000 substation automation system. The front-end unit integrates protection, measurement, and remote control functions. In addition to performing protection functions, it collects remote control-related information such as AI and DI, and sends it to the LONWORKS network in message form. The Master receives these messages through the LONWORKS network, obtains the information needed by the dispatcher, and transmits it to the dispatcher in remote control message form. Commands sent from the dispatcher first reach the Master, which unpacks them and then sends commands to the corresponding front-end unit in the format of its internal protocol. In short, the Master and the front-end unit communicate via the LONWORKS network in the form of network messages. Since the front-end unit integrates protection, measurement, and remote control, only one set of secondary cables is needed. Compared with the wiring method of traditional RTU, this method can save a lot of secondary cables, and the wiring is simple, greatly reducing investment. [img=358,228]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dwjs/dwjs9902/image2/54.gif[/img] Figure 1 Simplified diagram of CSC2000 substation automation system 1.2 Hardware structure of MASTER [img=377,163]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dwjs/dwjs9902/image2/55.gif[/img] Figure 2 Main design diagram of MASTER CPU board The CPU board is the core of the MASTER board, and it has two CPUs. Neuron 3150 is a network communication CPU that communicates with the front-end unit via the LONWORKS network. M77 handles the processing of messages within the substation and responds to scheduling commands. The two CPUs work in parallel. 1.3 Software Structure of MASTER The MASTER software adopts a modular design approach, and the software is divided into two layers: (1) The bottom layer is the processing module for LONWORKS network messages within the substation. (2) The upper layer is the remote control protocol processing module. The functions of the upper and lower layers are isolated from each other, and they are connected through a real-time database. The advantage of this structure is that when interfaced with different remote control protocols, the designer only needs to make local modifications to the upper-layer module, which greatly reduces the workload and speeds up the development process. 1.4 Technical Features of MASTER (1) It is a completely distributed RTU. Its telemetry, remote signaling, remote control, and remote pulse are all distributed, so the configuration is very flexible. (2) Large capacity and easy expansion, which can meet the capacity requirements of the automation station for remote control. If you want to add a telemetry, remote signaling or remote control, you only need to modify the address mapping table in a MASTER. A MASTER can use multiple RTU addresses to communicate with the dispatcher, and its capacity is several times that of a conventional RTU. There is no additional cost when increasing the capacity of the MASTER, and it is convenient and easy to do. (3) Simple and convenient interface with the front-end unit. The communication between the MASTER and the front-end unit is entirely in the form of network messages, so it can easily complete many operations that are difficult for conventional RTUs to complete, such as remote setting of protection settings and switching of protection pressure plates. (4) Simple installation. After the front-end unit in a station is installed and the network cable is connected, you only need to connect the MASTER to the network and connect the power supply to complete the electrical installation. [b]2 Siemens 8890 Remote Terminal Protocol[/b] The Siemens 8890 Remote Terminal Protocol is a protocol series, which mainly includes the following protocol types: (1) "8890 Remote Terminal Unit, Control Data Type Ⅱ, RTU Communications Protocol" (Publication Number: 60467950) (2) "8890 Remote Terminal Unit, Control Data Type Ⅰ, RTU Communications Protocol" (Publication Number: 60467940) (3) "8890 Remote Terminal Unit, Control Data Synchronous Type Ⅱ, RTU Communications Protocol" (Publication Number: 60467990) (4) "8890 Remote Terminal Unit, Control Data Asynchronous Type Ⅱ, RTU Communications Protocol" (Publication Number: 60467991) Since the dispatching systems introduced in China all use protocol (1), this article only introduces protocol (1). Unless otherwise specified, when referring to the 8890 protocol in this text, it refers to protocol (1). 2.1 Data Types in the 8890 Protocol Like other protocols, the 8890 protocol also has several basic data types, such as telemetry, remote signaling, electricity consumption, SOE, and remote control. Among them, remote signaling has three subcategories: simple state remote signaling, state change remote signaling represented by one bit, and state change remote signaling represented by two bits. In this way, remote signaling can be monitored and examined more comprehensively, such as the three states of circuit breaker: open, closed, and under maintenance. Each type of data has its own sequence number range, and the dispatching end distinguishes different types of data based on the sequence number. The remote control point has its own control object number, which is different from other data types. 2.2 Scanning Method in the 8890 Protocol The 8890 protocol is a query-response protocol, and the communication mode is half-duplex. When no remote control or time synchronization commands are sent, the dispatching end scans the substation end periodically. The 8890 protocol has the following four scanning modes: (1) SCAN 1: Requires the substation to return all telemetry and tele-signaling data. (2) SCAN 2: Requires the substation to return all tele-signaling data. (3) SCAN 3: Requires the substation to return all data within the required sequence number range. (4) SCAN3X: Requires the substation to return the corresponding data in the corresponding 3X configuration table. Among them, the SCAN3 mode is the most flexible. The dispatcher can use it to scan data in any sequence number range, and the start and end points of the range can be arbitrarily given by the dispatcher. When the secondary wiring sequence of the RTU in the station is not standardized, such as in the renovation of an old station, a special scanning sequence can be generated using the 3X configuration table in the 8890 protocol, and the dispatcher can then use the SCAN3X mode to scan the substation data. 2.3 Several typical commands in the 8890 protocol The remote control commands in the 8890 protocol are divided into two types: direct remote control and selective remote control. Direct remote control means that the dispatcher sends a remote control command to the substation, and the substation executes the command directly after receiving it. Selective remote control refers to the dispatching end first sending a remote control selection command to the substation end. After receiving the command, the substation end sends a remote control confirmation message back to the dispatching end. The dispatching end sends a remote control execution or remote control cancellation command to the substation according to the nature of the returned message. After the substation completes the remote control operation, it must report the result to the dispatching end. The remote control point of the 8890 protocol must have a corresponding remote signaling point; otherwise, the dispatching end will not be able to perform normal remote control operations. Although the 8890 protocol has two remote control modes, according to past practice, only the selective remote control mode is generally used in China, and the direct remote control mode is not used. The adjustment of transformer taps in the domestic dispatching system is generally completed by remote control. However, the 8890 protocol uses the set point command to complete the adjustment of transformer taps, so appropriate modifications must be made to suit the domestic dispatching habits. 2.4 Comparison of 8890 Protocol with Other Protocols Compared with other domestic question-and-answer remote control protocols such as N4F, SC1801, and DNP3, the 8890 protocol has the following characteristics: (1) The command structure is clear, the meaning is clear, and the total number of commands is relatively small. The total number of commands in the 8890 protocol is less than that of other question-and-answer protocols, only about half that of protocols such as N4F and SC1801. The commands in the 8890 protocol are clear and easy for users to understand and operate. The commands in protocols such as N4F and SC1801 are much more complex. When there is no operation such as time synchronization or remote control, the 8890 dispatch terminal simply sends a scan command to the substation, while the N4F and SC1801 protocols are much more complex. (2) The data link is more complex. The data link layer of the 8890 protocol is more complex than other protocols. In addition, it requires half-duplex communication mode, so the cooperation between the remote control equipment at the substation and the front-end machine at the dispatch terminal is more complex. In this respect, the N4F and SC1801 protocols are much simpler. (3) The debugging is more complex. Since the front-end machine at the 8890 dispatch terminal cannot directly observe the remote control messages sent by the substation, it is necessary to use the special debugging device provided by Siemens to cooperate with the debugging of the substation. Due to the imperfections in the circuit design of this debugging device, it may sometimes interfere with the equipment at the substation end, which requires the debugging personnel to distinguish between the genuine and the fake. The database of the substation and the database of the scheduling end must also meet some requirements, otherwise the database of the scheduling end will not work properly, and there may even be a possibility of the entire database of the scheduling end crashing. The debugging of protocols such as N4F and SC1801 is much simpler. 3 Implementation of the interface between CSC2000 system and 8890 protocol The software system block diagram is shown in Figure 3. The functions and interrelationships of each module are as follows: [img=527,326]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dwjs/dwjs9902/image2/56.gif[/img] Figure 3 Software system block diagram (1) System initialization This module completes the initialization of the two CPUs on the CPU board, serial communication chip and other hardware. (2) The main loop clears the watchdog inside and outside the chip and checks various flag words. Once a flag word changes, the corresponding module is executed. (3) The monitoring and processing module drives the station alarm and accident signals according to the flag word change information, calls the remote control processing module or the station communication module, and issues station control commands or remote control messages according to the relevant protocol format (8890 protocol or CSC2000 internal protocol). (4) Remote communication processing module This module implements the conversion function between 8890 protocol and CSC2000 internal protocol messages and remote communication management function. With the help of the address correspondence table of the two protocols inside and outside the station, it searches the real-time database. (5) Database module This module mainly completes the updating and management of the real-time database. Due to space limitations, the specific implementation of each of the above modules will not be described in detail in this article. [b]4 References[/b] 1 CDT Cyclic Telecontrol Protocol. Beijing: China Water Resources and Electric Power Press, 1991. 2 8890 Remote Terminal Unit, Control Data Type II, RTU Communication Protocol. Siemens Energy & Automation, Inc., 1994.