Introduction to the Characteristics of Computer Relaying for Power Systems

Computer relaying for power systems is composed of high-integration, bus-out chip microcontrollers, high-precision current and voltage transformers, high-dielectric strength export intermediate relays, and high-reliability switching power supply modules and other components.


Computer Relaying for Power Systems


1. Composition of computer relaying for power systems


Computer relaying for power systems is mainly used for power plants, substations, distribution stations, etc. with a voltage level of 110KV and below. It can also be used as protection and measurement and control of voltage and current in systems with voltage levels between 70V and 220V.


The traditional relay protection device makes the input current and voltage signals directly compare and operate between the analog quantities, so that the analog quantities can be compared with the given mechanical quantities (such as spring torque) or electrical quantities (such as threshold voltage) in the device. Carry out comparison and calculation processing to decide whether to trip or not.


The computer system can only do digital operations or logic operations, so the working process of the microcomputer protection is roughly: when the power system fails, the faulty electrical quantity is converted into a digital quantity through the analog quantity input system, and then sent to the central processing unit of the computer. The fault information is calculated according to the corresponding protection algorithm and program, and the result of the calculation is compared with the given setting value at any time to determine whether a fault occurs. Once it is confirmed that a fault occurs in the area, according to the status of the current circuit breaker and tripping relay of the digital input, a trip signal is sent through the digital output system, and the fault information is displayed and printed.


Microcomputer protection consists of hardware and software.


The software of microcomputer protection is composed of initialization module, data acquisition management module, fault detection module, fault calculation module, self-test module and so on.


Usually the hardware circuit of microcomputer protection is composed of six functional units, namely data acquisition system, microcomputer main system, switching input and output circuit, working power supply, communication interface and man-machine dialogue system.


2. Advantages of computer relaying for power systems


Product features: ultra-thin volume, powerful function, excellent workmanship, beautiful appearance, high cost performance.


3. Product features of computer relaying for power systems


In addition to the advantages of computer protection mentioned above, computer relaying for power systems has the following characteristics compared with similar products:

3.1 Complete variety: Microcomputer protection devices are particularly complete in variety, which can meet various protection requirements of various equipment in various types of substations and distribution stations, which provides great convenience for the design of substations and distribution stations and computer networking.


3.2 The hardware adopts the latest chips to improve the advanced technology. The CPU adopts 80C196KB, which is measured as 14-bit A/D conversion. There are as many as 24 analog input circuits. The collected data is processed by DSP signal processing chips. Fourier transform, to get the fundamental wave to the 8th harmonic, and the special software automatically corrects to ensure the high precision of the measurement. Using dual-port RAM and CPU to transform data, a multi-CPU system is formed, and CAN bus is used for communication. It has the characteristics of high communication rate (up to 100MHZ, generally running at 80 or 60MHZ) and strong anti-interference ability. The on-site observation and the setting of various protection modes and protection parameters can be conveniently carried out through the keyboard and liquid crystal display unit.


3.3 Hardware design Special isolation and anti-interference measures are adopted in the power supply, analog input, digital input and output, communication interface, etc., and the anti-interference ability is strong. In addition to the centralized group screen, it can be directly installed on the switch cabinet.


3.4 The software has rich functions. In addition to completing various measurement and protection functions, it can complete fault recording (1 second high-speed fault recording and 9 second fault dynamic recording), harmonic analysis and small current grounding line selection by cooperating with the upper processing computer. and other functions.


3.5 RS232 and CAN communication methods can be selected, support multiple telecontrol transmission protocols, and facilitate networking with various computer management systems.


3.6 It adopts 240×128 large-screen LCD liquid crystal display with wide temperate background, which is easy to operate and beautiful in display.


3.7 High integration, small size, light weight, convenient for centralized panel installation and decentralized installation on the switch cabinet.


4. Development of computer relaying for power systems


With the rapid development of computer technology, its extensive and in-depth application has brought a profound impact on various fields of engineering technology. The research and development of microcomputer protection in power system is an important part of the online application of computer technology. The application and promotion of microcomputer protection has become the development direction of relay protection.


As early as the end of the 1960s, G.D. Rockefiler and others proposed to use a computer to form a relay protection device. The research work at that time was based on a small computer, trying to use a small computer to realize multiple electrical equipment or the entire transformer. This has laid a theoretical foundation for the research and development of computer protection algorithms and software, and is a major turning point in the field of relay protection.


In the 1970s, a large number of papers on various algorithm principles and protection forms of computer protection were published. At the same time, with the development of large-scale integrated circuit technology, especially the advent of microprocessors and the decline in prices year by year, computer protection entered the practical field. In the first stage, a batch of microcomputers with sufficient functions appeared, and soon formed a product series. In 1977, Japan invested in a microprocessor-based control and relay protection device. In 1979, the Education Committee of the Institute of Electrical and Electronics Engineers (IEEE) organized a worldwide computer relay protection research class. In 1987, 70% of the total output value of relay protection equipment in Japan was computer protection products.


The research on microcomputer protection in China started in 1979. Although it started late, it made rapid progress. In 1984, the first 6809 (CPU) based microcomputer distance protection device prototype developed by North China Electric Power Institute and Nanjing Automation Equipment General Factory passed the appraisal and was put into trial operation. At the end of 1984, my country's first academic conference on computer relay protection was held in Huazhong Institute of Technology, which marked that the development of computer protection in my country has entered an important stage of development. In the 1990s, various manufacturers launched new products almost every year, and many formed microcomputer protection products have been launched one after another. Up to now, thousands of sets of microcomputer line protection and main equipment protection have been produced in China every year. In the fields of transmission line protection, component protection, comprehensive automation of substations, fault recording and fault location, etc. All have achieved remarkable results. The third-generation microcomputer relay protection device with high reliability, high anti-interference level and network communication capability has been put into use in the power system. The research and manufacturing level of my country's microcomputer relay protection has reached the international level.


5. The operating principle of computer relaying for power systems


The digital core of the microcomputer protection device is generally composed of CPU, memory, timer/counter, Watchdog and so on. At present, the mainstream of the digital core is the embedded microcontroller (MCU), which is commonly referred to as a single-chip microcomputer; the input and output channels include analog input channels (analog input conversion loops (convert the quantities measured by CT and PT into lower suitable Internal A/D conversion voltage, ±2.5V, ±5V or ±10V), low-pass filter and sampling, A/D conversion) and digital input and output channels (man-machine interface and various alarm signals, trip signals and electrical pulses, etc.).

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