Current Situation and Development of Power System Relay Protection Technology

1 Development Status of relay protection

The rapid development of power systems puts forward new requirements for relay protection. The rapid development of electronic technology, computer technology and communication technology has continuously injected new vigor into the development of relay protection technology, therefore, the relay protection technology is advantageous and has completed four historical stages of development in more than 40 years.
After the founding of the People's Republic of China, China's relay protection disciplines, relay protection design, relay manufacturing industry and relay protection technical teams from scratch, it took about 10 years to walk the path of a half century in an advanced country. In 1950s, our engineering and technical personnel creatively absorbed, digested, and mastered the performance and operation technology of Foreign Advanced Relay Protection Equipment [1], the establishment of a relay protection technical team with profound theoretical accomplishments and rich operation experience played a guiding role in the establishment and development of the national relay protection technical team. Acheng relay factory introduced and digested the Advanced Relay manufacturing technology at that time, and established our own relay manufacturing industry. Therefore, in 1960s, China established a complete system for research, design, manufacturing, operation and teaching of relay protection. This is an era of electromechanical relay protection, which lays a solid foundation for the development of relay protection technology in China.
Since the end of 1950s, transistor relay protection has been under research. From the 1960s s to the 1980s s, it was an era in which transistor relay protection was booming and widely used. Among them, the high-frequency protection of 500kv transistor direction and the high-frequency locking distance protection of transistor developed by Nanjing electric power automation Research Institute are jointly studied by Tianjin University and Nanjing electric power automation equipment plant, it runs on the Gezhouba 500 kV line [2] and ends the era in which the protection of the kV Line relies entirely on imports from abroad.
During this period, the integrated circuit protection based on the integrated operational amplifier has been studied since 1970s. By the end of 1980s, integrated circuit protection has formed a complete series, gradually replacing transistor protection. By the beginning of 1990s, the development, production and application of integrated circuit protection were still in the dominant position. This is the era of integrated circuit protection. In this regard, the high-frequency protection of the frequency variation direction of the integrated circuit developed by Nanjing electric power automation Research Institute plays an important role [3], the phase voltage compensation type of the integrated circuit developed by Tianjin University and Nanjing power automation equipment factory for high-frequency protection also operates on multiple 220kv and 500kv lines.
China has started research on computer relay protection since the end of 1970s [4]. Universities and research institutes play a leading role. Huazhong University of Science and Technology, Southeast University, North China Electric Power College, Xi'an Jiaotong University, Tianjin University, Shanghai Jiaotong University, Chongqing University, and Nanjing electric power automation Research Institute have successively developed different principles and different types of computers. protection device. In 1984, the microcomputer protection device for transmission lines originally developed by China North Electric Power University first passed the identification and was applied in the system [5]. It opened a new page in the history of China's relay protection development, it opened up the road for the promotion of microcomputer protection. In terms of Main Equipment Protection, the loss protection, generator protection and generator developed by Southeast University and Huazhong University of Science and Technology? Transformer Group protection was also put into operation in 1989 and 1994. The Microcomputer line protection device developed by Nanjing electric power automation Research Institute also passed the identification in 1991. High-frequency microcomputer phase voltage compensated Type Protection developed by Tianjin University and Nanjing Electric Power Automation Equipment Factory, the forward-order fault component direction high-frequency protection developed by Xi'an Jiaotong University and xuchang relay factory also passed the identification in 1993 and 1996. At this point, the protection of microcomputer lines and main equipment with different principles and models has their own characteristics, providing a new generation of excellent performance, complete functions, and reliable protective equipment for the power system. With the study of microcomputer protection devices, many theoretical achievements have been made in computer protection software and algorithms. It can be said that China's relay protection technology has entered the era of microcomputer protection since 1990s.

2 future development of relay protection

Future Trend of relay protection technology is the integration of computer, network, intelligence, protection, control, measurement and data communication.

2.1 Computerization
With the rapid development of computer hardware, the Computer Protection hardware is also evolving. The Microcomputer line protection hardware developed by the North China Electric Power Institute has gone through three stages of development: from the advent of eight-Bit Single-CPU microcomputer protection, it has developed into a multi-CPU Structure in less than five years, later, it was developed into a big module structure with no modules in the bus, which greatly improved the performance and has been widely used. The microcomputer protection developed by Huazhong University of Science and Technology also evolved from 8-bit CPU to 32-bit microcomputer protection based on the core part of the industrial computer.
At the beginning, Nanjing electric power automation Research Institute developed 16-bit CPU-based microcomputer line protection, which has been widely promoted. Currently, 32-bit protection hardware systems are also being studied. The hardware of the Microcomputer master equipment developed by Southeast University has also been improved and improved several times. At the beginning, Tianjin University developed a microcomputer line protection based on 16-bit multi-CPU. In 1988, a 32-bit digital signal processor (DSP) was developed) the integrated microcomputer device for protection, control, and measurement has been developed in cooperation with Zhuhai jindian automation equipment company into a fully functional 32-bit large module, one module is a small computer. The 32-bit microcomputer chip is not only focused on precision, because the accuracy is limited by the resolution of the/D converter, when the 16-bit is exceeded, the conversion speed and cost are unacceptable; more importantly, the 32-bit microcomputer chip has a high degree of integration, high operating frequency and computing speed, a large addressing space, a wide range of command systems and a large number of input and output ports. The registers, data bus, and address bus of the CPU are all 32-bit. They have the memory management function, memory protection function, and task conversion function) and floating point components are integrated into the CPU.
In addition to the basic functions of protection, the power system must have a long-term storage space for large-capacity fault information and data, fast data processing, and powerful communication capabilities, networking with other protection, control devices, and scheduling devices to share the capabilities of the entire system's data, information, and network resources, as well as advanced language programming. This requires that the microcomputer protection device has the function equivalent to a PC. At the early stage of Computer Protection Development, we had imagined using a small computer as a relay protection device. This idea was unrealistic because the minicomputer was large in size, high in cost, and poor in reliability. At present, the functions, speed, and storage capacity of the industrial computer similar to that of the microcomputer protection device have greatly exceeded those of the current minicomputer. Therefore, it is time to use a complete set of Industrial Computer for relay protection, this will be one of the development directions of microcomputer protection. Tianjin University has developed a relay protection device using an industrial computer with the same structure as the microcomputer protection device. The advantages of this device are as follows: (1) It has all the functions of the 486pc machine and can meet various functional requirements for current and future microcomputer protection. (2) the dimension and structure are similar to the current microcomputer protection device. They have excellent technology, shockproof, anti-overheating, and anti-electromagnetic interference capabilities, and can run in very bad working environments, cost acceptable. (3) using STD bus or PC bus, modular hardware, different modules can be selected for different protection, flexible configuration and easy expansion.
The computer-based and computer-based protection devices are irreversible development trends. However, a detailed and in-depth study is required on how to better meet the requirements of the power system, how to further improve the reliability of relay protection, and how to achieve greater economic and social benefits.

2.2 Networking
As a tool for information and data communication, computer networks have become the technical pillar of the information age, making fundamental changes in human production and social life. It has a profound impact on various industrial fields and also provides powerful communication means for various industrial fields. So far, except for Differential Protection and vertical protection, all the relay protection devices can only reflect the electrical capacity of the protection installation. The function of relay protection is only limited to removing faulty components and narrowing down the scope of impact of the accident. This is mainly due to the lack of strong data communication techniques. The concept of system protection has already been put forward in foreign countries. At that time, it mainly referred to the safety of automatic devices. Because the function of relay protection is not only limited to removing faulty components and limiting the impact scope of accidents (this is the primary task), but also to ensure the safe and stable operation of the whole system. This requires that each protection unit can share the system-wide operation and fault information data. Each Protection Unit and relay device can coordinate the operation based on the analysis of the information and data, ensure secure and stable system operation. Obviously, the basic condition for implementing the system protection is to connect the protection devices of the main equipment in the whole system with a computer network, that is, to achieve the network of the microcomputer protection device. This is entirely possible under the current technical conditions.
For general non-system protection, achieving computer networking of protection devices also has great benefits. The more system fault information the relay protection device can obtain, the more accurate the determination of the fault nature, fault location, and fault distance detection. The Study on the Adaptive protection principle has been a long time and has made some achievements. However, it is necessary to realize the self-adaptive protection on the system running mode and fault status, more system operation and fault information must be obtained. This can be achieved only when the computer that implements protection is networked.
For some protection devices, computer networking can also improve the reliability of protection. In, Tianjin University proposed a principle of Distributed Bus Protection for the Super High Voltage multi-circuit bus of the Three Gorges Hydropower Station. The principle is to distribute the traditional centralized bus protection into several bus protection units (the same as the number of circuits of the bus to be protected) and install them on the Protection screens of various circuits, each Protection Unit is connected by a computer network. Each Protection Unit only inputs the electric traffic of the current loop, converts it into a digital volume, and transmits it to the protection units of all other circuits through a computer network, each protection unit calculates the Busbar Differential Protection Based on the Current Circuit's electrical traffic and the electrical traffic of all other circuits obtained from the computer network, if the calculation result shows that it is a fault within the bus, only the circuit breaker is switched on and the faulty bus is isolated. When a fault occurs outside the bus area, each Protection Unit is calculated as an external fault. This distributed bus protection principle implemented by computer networks has higher reliability than the traditional centralized bus protection principle. If a protection unit is moved incorrectly due to interference or miscalculation, the current loop can only be jumped in incorrectly. This will not cause a major accident that will completely remove the busbar, this is very important for the system hubs with ultra-high voltage busbars like the Three Gorges Power Station.
From the above, we can see that the network of the microcomputer protection device can greatly improve the protection performance and reliability, which is an inevitable trend of the development of the microcomputer protection.

2.3 integration of protection, control, measurement and data communication
Under the condition of computer-based and network-based relay protection, the protection device is actually a high-performance, multi-functional computer and an intelligent terminal on the computer network of the entire power system. It can obtain any information and data about the operation and failure of the power system from the Internet, or transmit any information and data of the protected components it receives to the network control center or any terminal. Therefore, each microcomputer protection device can not only complete the relay protection function, but also complete the measurement, control, and data communication functions in the case of normal operation without faults, that is to say, the integration of protection, control, measurement and data communication is realized.
At present, for the purpose of measurement, protection and control, all devices in the outdoor substation, such as transformer and line, must be directed to the main control room using control cables. The large number of control cables laid requires a lot of investment, and the secondary circuit is very complicated. However, if the above-mentioned computer device integrating protection, control, measurement, and data communication is installed locally beside the protected device of an outdoor substation, after the voltage and electrical flow of the protected device are converted into digital values in the device, the device is sent to the main control room through a computer network, which can eliminate a large number of control cables. If optical fiber is used as the transmission medium of the network, electromagnetic interference can be avoided. Now the photocurrent Transformer (OTA) and photovoltage Transformer (OTV) are in the research and test phase and will be applied in the power system in the future. When OTA and OTV are used, the protective device should be placed closest to Ota and OTV, that is, near the protected device. The optical signals of OTA and OTV are input into the Integrated Device and converted into electrical signals. On the one hand, they are used for Protection Calculation and judgment. On the other hand, they are sent to the main control room through the network as the measurement volume. From the main control room, operation control commands for the protected device can be sent to the integrated device through the network, thereby the integrated device performs the operation of circuit breaker. In 1992, Tianjin University proposed the integration of protection, control, measurement and communication, and developed an Integrated Device for protection, control, measurement, and data communication based on the DSP.

2.4 intelligence
In recent years, artificial intelligence technologies such as neural networks, genetic algorithms, Evolutionary Planning, and fuzzy logic have been applied in various fields of power systems, research on application in the field of relay protection has also started [7]. Neural networks are a non-linear ing method. Many complex non-linear problems that are difficult to list equations or to solve are solved by applying neural networks. For example, when the system potential angle on both sides of the transmission line is open, short-circuit through the transition resistance is a non-linear problem. Distance Protection is difficult to identify the fault location correctly, resulting in misoperation or rejection; if the neural network method is used and a large number of fault samples are trained, the samples can be correctly identified in the event of any fault as long as the samples fully consider various situations. Others, such as genetic algorithms and Evolutionary Planning, have their unique capabilities to solve complex problems. The appropriate combination of these artificial intelligence methods can make the solution faster. Since 1996, Tianjin University has studied neural network type relay protection and achieved initial results [8]. It is foreseeable that artificial intelligence technology will be applied in the field of relay protection to solve problems that are difficult to solve using conventional methods.

3 conclusion

Since the founding of the People's Republic of China, China's power system relay protection technology has gone through four times. With the rapid development of power systems and advances in computer and communication technologies, the relay protection technology is facing a trend of further development. The Development Trend of relay protection technologies at home and abroad is: computer, network, protection, control, measurement, data communication integration and artificial intelligence, which puts forward arduous tasks for relay protection workers, it also opened up a wide range of activities.

Author: Tianjin Electric Power Society (Tianjin 300072)

References
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