Substation automation technology has developed rapidly in recent years, and many substation automation systems have been put into operation. Microcomputer protection, which is an important part of the substation automation system, has also achieved rapid development. The microcomputer protection device has achieved remarkable results in terms of speed of operation, correct operation rate, operational reliability and ease of use. The traditional analog protection has been inconsistent with it, but the full use of the characteristics of the microcomputer and Advantages and other aspects still have great development potential. In the realization of relay protection function, it also has other functions (such as control, measurement, communication, etc.) to form a microcomputer integrated protection device, and other secondary devices in the substation automation system. In terms of configuration and management, there is still room for optimization design. According to the status quo of microcomputer integrated protection in substation automation at home and abroad, this paper discusses its system composition and function configuration with optimization design ideas, and puts forward some ideas for its optimization design.
2 Functional requirements of substation automation system for microcomputer protection
2.1 Protection functions should be relatively independent
Ensuring safe and stable operation of relay protection is the basic requirement for designing substation automation systems. Due to the special nature of relay protection, the automation system must not reduce the reliability of relay protection. Due to the requirement for rapid decision-making and rapid response of the microcomputer protection device, it requires higher reliability and sensitivity, so it still needs to maintain relative independence in function and function. In the system operation, the reliability of the relay protection unit should be related only to the protection device itself, and to other devices related to the protection unit (such as communication port, network, monitoring unit, etc.). This requires that the protection unit be relatively independent in the automatic function setting, and even if the network connected to the protection device fails, the reliability of the relay protection itself should not be affected.
2.2 Information Sharing
Under the premise of ensuring safe operation, information resources should be shared as much as possible in the design of substation automation system. In the measurement loop, protection, recording, instrumentation, metering, telecontrol, etc., can be classified and optimized according to different requirements of CT secondary characteristics, reducing measurement links, reducing secondary loop load, and improving measurement accuracy.
From the perspective of the entire power system automation field, computer communication technology has led to the development of various analog devices or systems in the digital direction, and the application of digital signal processing has further contributed to the informationization of these devices, and the main feature of informationization is The effective use and sharing of information can greatly improve the performance-price ratio of the device or system. For relay protection, the integration of various protection functions will be realized through information sharing, and it is also conducive to the realization of integrated automation optimization design of substation. .
With the development of power systems, both power system analysis and application software, as well as management, monitoring and control systems, are becoming larger and larger. If traditional functional-oriented design methods are still used, these systems will be developed. Modifications and extensions are becoming more and more difficult, unnecessary repetitive settings are increasing, productivity is difficult to improve, and object-oriented design methods are the best choice for solving these problems.
In the early substation, due to the limitation of the computer hardware level, the protection function and the telecontrol function were separately implemented separately, and the functional units were basically classified according to the information type (ie, by profession). With the development of process control architecture and the advancement of computer communication technology, the object-oriented distributed structure is used in the substation to form a field protection control system, which shows its strong vitality.
The so-called object-oriented distributed structure is to configure the field-level unit according to the configuration principle of the primary device and the secondary protection device. One primary device interval corresponds to one secondary protection monitoring unit, and the protection is placed underground, which reduces the CT burden and greatly saves two. The secondary cable and secondary circuit load will be further reduced, and the control room area will be further reduced, which makes the system configuration and operation more convenient, and improves the system troubleshooting and adjustment operation speed. At the same time, each protection unit is connected to the station control level equipment through the bus, and the protection engineer station is used to carry on and off, so that the concept of on-site maintenance process is clear and the responsibility is clear. In addition to the protection and management functions of the conventional automation, the substation can also realize the adaptive adjustment of the protection unit through the on-site high-speed bus; the open-type station-level network interface can be easily established to establish contact with the management level, which fully guarantees the system. Interoperability and scalability. In this way, the important fast decision function of relay protection can be realized at the field level, and the comprehensive protection involving multiple points and the adaptive function related to the system structure are coordinated by the engineering station and the field bus.
Standardization and modularization are the basic requirements for ensuring the independence and scalability of substation automation systems. However, due to the lack of a unified design plan and product standards in this respect in China, this kind of blooming situation has also caused repeated labor to the power research and production industry to a certain extent. Many products of different manufacturers are self-contained, mutual Lack of good compatibility and scalability, causing great trouble for users. Therefore, the modularization and standardization of protection software and hardware design should be established to ensure the independence of the system itself and compatibility with other systems.
4.1 Principles of module determination
4.1.1 Decomposition module with function as the core
A module is a product composition pattern that is a combination of common components (modules). A module is a stand-alone unit with certain functions. The function is the basis for the module and the basis for system decomposition. Module decomposition should be hierarchical. Such as: (1) basic modules (such as power plug-ins, etc.). A feature that is a plug-in unit is a stand-alone unit with specific functions. (2) Plug-in module. The plug-in module consists of a plug-in box with independent integrated functions. (3)) Product level modules. It can be composed of plug-in-level modules and has a variety of cabinet screens for protection control and measurement functions.
4.1.2 Modules should be typical
The requirements of many similar functions between various protection devices are simplified, unified, merged into one or several typical functional units, and then these typical functional units are separated from the product to make them function, parameters and The interface aspect is a stand-alone unit with specific functions that can be used in a variety of product systems. The significance of this paradigm is to eliminate unnecessary duplication and diversity of modules in function.
4.2 Modularization of hardware
The modularization of the hardware starts from the basic module. When the system is decomposed into modules, the cohesion of the module should be the largest, and the decomposition point is selected at the least and weakest part of the interface, which simplifies the interface structure and makes the system easy to decompose. It is also easy to combine the basic module design into a plug-in type, and the common protection hardware can be used in different protection rooms, thus shortening the development cycle and ensuring the convenience of production, debugging and maintenance. The main plug-ins are: power plug-in, AC plug-in, CPU plug-in, open-in plug-in, etc. Different basic module combinations of hardware can form a plug-in module, and different plug-in module combinations can form a product-level module.
4.3 Modularization of the software
Like the hardware, the software of each processing module also adopts a modular structure. In the whole, the software module and the hardware module are set together, and the advantages of high software development and copying rate, flexibility, consistency, and high reliability should be fully utilized. Derived new products, that is, the same hardware, derived from the software to meet new requirements or meet the special requirements of users. At the same time, the modularity of the software also helps to shorten the software development cycle. For the protection of the shared main program, interrupt sampling program, human interface program, start interrupt program communication program and GPS synchronization program, the protection device can be flexibly copied and utilized.
It should be pointed out that the modular product system in practical application is dynamic, and modularization not only has a process of formation, perfection and maturity, but with the continuous updating of technology, people's understanding is deepening and product reliability requirements. Constantly improving. Therefore, the module system is not only inevitable, but also necessary for the implementation of the new and timely modification and update. However, in terms of modification and update, there is inheritance in both the circuit and the mechanical structure. Its unique superiority. This is also the advantage of modular design.
5.1 Analysis of Microcomputer Integrated Protection Information Flow in Substation
The data related to the comprehensive protection of the substation and the microcomputer has three flow directions: the first flow direction is to protect the equipment to the substation upper monitoring machine, and mainly transmits information reflecting the running status of the primary system: the second flow direction is from the upper monitoring machine to the protection device, usually The upper monitoring machine issues the modification parameter command and some other control information for the protection device; the third flow direction is the horizontal data exchange between the protection devices, such data depends on the system design and function division, for example: if the device is required to be protected Simultaneous sampling, the horizontal amount of data exchange is large. At the current stage, considering the independence of the protection unit and reducing the dependence of the system on communication, the communication between the protection devices mainly considers the communication problem between the distributed protection device and the unit monitoring device. Since the two devices are usually in very close proximity, conventional serial communication techniques can be used to solve them.
5.2 Communication System Configuration Principles
The structural configuration of the substation communication system shall be arranged according to the design principle of the distributed system, and the calculation and processing capacity shall be arranged to the information source point, and the collection and processing shall be performed nearby, and the nearest control shall be carried out. Only the necessary information involved in the coordinated control shall be transmitted to each other. In order to improve system operation efficiency, reduce the dependence of the system on communication, and improve the reliability of the overall system.
5.3 Communication mode selection
The network topology of the local area network in the substation mainly adopts the star and bus type connection.
The star communication mode is the center point of the above-mentioned monitoring machine, and is connected to the control I/O device and the protection device distributed on each switch cabinet through the communication cable in a divergent manner. The medium is generally selected from optical fibers, so it has the characteristics of natural isolation, high anti-interference and high security of optical communication. It is suitable for use in the harsh environment of substation, and each I/O unit and protection unit are independent of the station-level computer. Communication, exclusive communication line, maintainability. Therefore, many substation automation systems currently use a star communication system solution. However, the total length of cables required for star connection is higher than that of other structures. Especially when the station-level computer has more wiring, the construction is complicated; the horizontal communication between each I/O unit and the protection device must be performed by the station-level computer. Complex and inefficient; when using fiber-optic communication technology, because the fiber itself is difficult to achieve T-connection, the bus structure cannot be realized unless fiber ring technology is adopted. Therefore, active photoelectric conversion equipment must be used, which is bound to cause the reliability of the communication system to be limited by the reliability of each connection point. Therefore, it is recommended to consider carefully when choosing a star communication system solution.
With the development of communication technology, for the application environment of substation automation technology, there is a consensus on more and more people about field-level communication, that is, using a bus-type network to form a multi-redundant system, each node on the network can Other nodes communicate; the required total cable length is short and the reliability is high, unlike the star open connection method, which has a reliability bottleneck formed by a central control node (station level computer). Here, we recommend an international new generation of on-site measurement and control network CAN. The technical solution based on CAN network is easy to realize dual network backup, and can integrate with I/O unit and protection unit to realize high-speed data exchange, which can ensure the real-time of emergency information, strong anti-interference ability, low cost and simple construction.
It should be pointed out that the communication between devices of different manufacturers in the substation has not yet established a unified interface standard in China, and there are many kinds of communication protocols, which not only requires a large amount of software and hardware development manpower, but also the user's equipment selection. Operation, maintenance, etc. bring a lot of inconvenience. The choice of the protocol not only affects the reliability and efficiency of the communication system, but also affects the reliability and efficiency of the communication system, and also affects the normal function of the system. Therefore, we should pay close attention to the standardization of the communication system protocol in the substation automation system, accelerate the implementation of the national standards equivalent to the adoption of the IEC870-5 series of international standards, and promote the implementation of work, avoid duplication of labor, improve labor productivity, and fully utilize automation. Technical advantages.
Microcomputer protection is the development direction of future protection. The existing domestic microcomputer protection device has well completed the conversion of protection from analog to digital, but still has great development potential in fully utilizing the advantages of microcomputer and enhancing protection.
6.1 Extended fixed value storage capacity
In the power system, the operation mode of the power grid is changed frequently. In order to meet the reliability, flexibility and quickness selectivity of the relay protection device in different operation modes, it is required to perform different operations in different operation modes. The setting value, if the operation mode is changed, the method of temporarily inputting the new fixed value on the site will bring a lot of inconvenience, mainly reflected in (1) complex fixed value needs relay protection maintenance personnel to go to the substation site to make changes, increase The maintenance amount; (2) The long time for the system to change the fixed value is not conducive to the safety of the system operation, especially when the change of the mode during the accident processing needs to be changed; (3) The simple setting is changed by the operator and is prone to error.
Therefore, for the microcomputer protection device, it should be possible to pre-select a variety of the most common and important operation modes, so as to formulate corresponding grid protection setting settings, and store the corresponding values ​​of these solutions in the protection of multiple settings. In the value zone, when the operation mode is changed, the operator can adjust the fixed value of the field protection device to adjust the fixed value of the relay protection. This is fast and accurate, and it solves the inconvenience of re-entering the fixed value on site. Improve the coordination ability of protection under various operating modes, and reduce the error rate of changing the fixed value.
6.2 Recording the protection device's own working information
The traditional analog relay protection can only record the output result or the event that occurred in the form of a signal light after completing some logic judgment, and the information content is small. Although the current microcomputer protection device can output protection actions and self-test information, it is similar to the traditional analog protection in providing work information. For microcomputer protection, it has powerful computing, logic judgment and storage capabilities, making it possible to record the protection device's own working information in detail.
Recording the protection device's own work information mainly has the following functions: (1) By recording its own work information, combined with fault recording, it is possible to scientifically, fairly, and realistically determine the action behavior of protection, not just inference; (2) It not only has important practical significance for the operation and maintenance of the protection device, but also has guiding significance for product development, development and improvement and improvement of product performance; (3) even if the protection device operates correctly, its own work information has reference value, such as analysis and protection. Whether the action speed and the action process meet the performance requirements of the product, and whether the protection action behavior is consistent with the fault development process.
The details of the work to be recorded by the protection device are: (1) the actual program direction when a self-test or action result is generated (can be output through the printer or serial port as needed); (2) the value of the protection action Area code, the data of each protection function action point; (3) the operation time of each main component or function and the opening and closing timing diagram of the action; (4) Among the multiple start amounts, indicate which conditions are met due to the conditions Wait. This information should not be lost after power down and can be sent to the dispatcher via the built-in Modem.
6.3 External input information record
Microcomputer protection can correctly make corresponding logical judgments based on different external information. Since these external information have a crucial influence on the program flow and even the action behavior of the microcomputer protection work, it is necessary to record in detail in order to accurately analyze the protective action behavior, especially the incorrect action that may occur under complicated working conditions. It can also output the external input timing sequence with standard GPS time scale and accurate to milliseconds as needed. From this, we should be able to see when each external information is input, how long it lasts, whether there is a gap in the middle, and so on.
6.4 Using GPS to Synchronize the Clock
The Global Positioning System (GPS) has a wide range of uses and is exploring new ways to develop power system monitoring, protection and control with its superior time synchronization performance.
Two time signals can be obtained from GPS: one is the second pulse signal, and the other is the date and time code corresponding to the leading edge of each second pulse, that is, the time stamp of the second pulse signal. In order to meet the needs of accident analysis, GPS should be used to acquire the synchronous clock, and the built-in GPS timing interface circuit can provide standard time for the protection device, such as the sampling pulse protected by the GPS pulse control, thus ensuring the same network. The sampled data of the model device is consistent in time.
The status quo and development of substation automation research requires that the integrated microcomputer protection that constitutes automation can operate reliably and independently, and can be expanded into a larger system and stronger functions. Therefore, it is necessary to strengthen the standardized design of microcomputer protection.
Due to the rapid development of science and technology, the development and development cycle of new products is getting shorter and shorter. Therefore, in the development of new products, we should consider the reliability, advancement and economy of the products, and adopt new ideas, new principles and new technologies to develop new microcomputer protection with high reliability and powerful functions. It can be predicted that with the development of China's power industry and the technological advancement of related industries such as electronic technology and industrial automation information engineering, the new-generation microcomputer protection device with better man-machine interface and safer and more reliable operation will achieve rapid development.
references
1 Content and functional requirements and configuration of Zhu Daxin and Liu Jue Substation Integrated Automation System, Power System Automation, 1995
2 Jiao Zhixian, Chen Yong, Li Shiyu and other substation integrated automation in the micro-machine protection should have the function "Power System Automation" 1996
3 Yan Zeyou, Yang Qixun, a new type of substation integrated automation system program "Relay" 1998
4 Zheng Sanbao, Shi Tiehong, etc. Design and Implementation of Complete Microcomputer Protection and Management in Substation
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