Substation is an indispensable part of the power system, which is responsible for the heavy task of power conversion and power redistribution, and plays a decisive role in the safety and economic operation of the power grid. In order to improve the safe and stable operation level of substations, reduce operation and maintenance costs, improve economic benefits, and provide users with high quality electric power service, the integrated automation technology of substations began to rise and has been widely used.
Substation integrated automation is the substation secondary equipment (including control, signal, measurement, protection and automatic device and remote device, etc.) application of computer technology and modern communication technology, through the function combination and optimization design of the substation implementation of automatic monitoring, measurement, control and coordination, communication and scheduling etc. Comprehensive automation system. The realization of substation comprehensive automation can improve the safety and economic operation level of power grid, reduce capital construction investment, and provide a means to popularize unmanned substation. The rapid development of computer technology, information technology and network technology drives the progress of substation integrated automation technology. In recent years, with the development of digital electrical measurement system (such as photoelectric transformer or electronic transformer), intelligent electrical equipment and related communication technology, substation integrated automation system is moving toward the digital direction.
I. Main functions of substation integrated automation system
The basic functions of substation integrated automation system are reflected in the functions of the following six subsystems:
1. Monitoring subsystem;
2. Relay protection subsystem;
3. Voltage and reactive power integrated control subsystem;
4. Low-frequency load reduction control subsystem of power system;
5. Standby power supply control subsystem;
6. Communication subsystem.
This part is quite rich, and there are many literatures on it in detail, so this article will not elaborate on it.
Two, traditional substation automation system
1. System structure
At present, the structure of substation integrated automation system at home and abroad can be classified into the following three types from the design idea [1] :
(1) Centralized
Using different grades of computer, expand its peripheral interface circuit, centralized collection of substation analog, switching and digital data and other information, centralized processing operations, respectively, to complete the microcomputer monitoring, microcomputer protection and some automatic control and other functions. Its characteristics are: high requirements for computer performance, scalability, poor maintainability, suitable for medium and small substations.
(2) distributed
Substations are divided according to monitored objects or system functions. Multiple cpus work in parallel, and data communication between cpus is realized by network technology or serial mode. The distributed system is easy to expand and maintain, and local faults do not affect the normal operation of other modules. This mode can be installed in a centralized or split screen mode.
(3) Decentralized distribution
Each data acquisition and control unit (I/O unit) and protection unit in the interval layer are installed on the switch cabinet or near other equipment in a decentralized manner. Each unit is independent of each other, interconnected only through the communication network, and communicates with the substration-level measurement and control main unit. Functions that can be performed at the interval layer are independent of the communication network, such as protection functions. Communication networks are usually optical fibers or twisted-pair cables, which maximize the compression of secondary equipment and cables and save construction investment. Installation can be dispersed in each interval, can also be concentrated in the control room group screen or stratified group screen, can also be part of the control room, the other part of the switch cabinet scattered on.
2. Existing problems
Substation integrated automation system has achieved good application effect, but there are also shortcomings, mainly reflected in: 1 the information interaction between the primary and secondary is still the continuation of the traditional cable connection mode, high cost, construction, maintenance inconvenience; 2. The secondary data collection part is largely repeated, which wastes resources; 3. Information standardization is insufficient, information sharing degree is low, multiple systems coexist, and the interconnection between devices and systems is difficult, forming information islands, and information is difficult to be comprehensively applied; When accidents occur, there will be a large number of event and alarm information, and the lack of effective filtering mechanism will interfere with the correct judgment of the fault by the operation personnel on duty.
Three, digital substation
Digital substation is the next stage in the development of substation automation, the state grid corporation of "11th five-year plan" science and technology development plan has explicitly put forward during the period of "11th five-year plan" to study the model of digital substation and construction station 2, and the current digitized substation to be built and put into operation, such as fuzhou digital substation of 110 kv in the exhibition.
1. Concept of digital substation
Digital substation refers to the substation in which the process of information collection, transmission, processing and output is completely digitized. The basic features are intelligent equipment, network communication and automatic operation management.
Digital substation has the following main characteristics:
(1) Intelligent equipment
Electronic transformer with digital output, intelligent switch (or traditional switch with intelligent terminal) and other intelligent primary equipment. Sampling values, status variables, control commands and other information are exchanged between primary and secondary devices by means of optical fiber transmission of digitally encoded information.
(2) Network of secondary equipment
Analog, switching and control command information are exchanged between secondary devices through communication network, and control cables are cancelled.
(3) Automation of operation management system
Automatic systems such as automatic fault analysis system, equipment health status monitoring system and programmed control system should be included to improve the level of automation and reduce the difficulty and workload of operation and maintenance.
2. Main technical characteristics of digital substation
(1) Digitalization of data collection
The main symbol of the digital substation is the use of digital electrical measurement system (such as photoelectric transformer or electronic transformer) to collect the current, voltage and other electrical parameters 3, realize the effective isolation of the primary and secondary systems in the electrical, increase the dynamic measurement range of electrical gas and improve the measurement accuracy. Thus it provides a basis for the transformation from conventional substation device redundancy to information redundancy and information integration application.
(2) Hierarchical distribution of the system
The development of substation automation system has experienced a transformation from centralized to distributed. The second generation of hierarchical distributed substation automation system mostly adopts mature network communication technology and open interconnection protocol, which can record the equipment information more completely and improve the response speed of the system significantly. The structure of digital substation automation system can be physically divided into two categories, namely intelligent primary equipment and network secondary equipment; In logical structure according to IEC61850 communication standard definition, can be divided into "process layer", "interval layer", "station control layer" three levels. High-speed network communication is used within and between different layers.
(3) Information interaction network and integration of information application
Digital substation adopts low power, digital new transformer to replace conventional transformer, and directly convert high voltage and high current into digital signal. Information interaction between devices in the station is carried out through high-speed network. There is no I/O interface with repeated functions in secondary devices. Conventional functional devices become logical functional modules to realize data and resource sharing. At present, IEC61850 is the international standard for substation automation communication.
In addition, digital substation secondary system device of originally scattered the function of information integration and optimization, so it can effectively avoid the conventional substation monitoring, control, protection, fault wave record, such as measurement and measurement device is the hardware configuration of repetition, information is Shared and problems such as large investment cost.
(4) Intelligent equipment operation
The new high voltage circuit breaker secondary system is established by microcomputer, power electronics technology and new sensors, the intelligence of the circuit breaker system by microcomputer control secondary system, IED and the corresponding intelligent software to achieve, protection and control commands can reach the unconventional substation secondary loop system through optical fiber network, Thus realize the digital interface with the circuit breaker operating mechanism.
(5) Equipment maintenance status
In the digital substation, it can effectively obtain the operation state data of the power grid and the fault and action information of various IED devices, and realize the effective monitoring of the operation and signal loop state. There are almost no unmonitored functional units in the digital substation, and there is no blind area in the collection of equipment state characteristic quantity. Equipment maintenance strategy can be changed from "regular maintenance" of conventional substation equipment to "state maintenance", thus greatly improving the availability of the system.
(6) The measuring principle of LPCT and the appearance of the tester
As mentioned above, LPCT is actually a kind of electromagnetic current transformer with low power output characteristics. In IEC standard, it is listed as a realization form of electronic current transformer, representing a development direction of electromagnetic current transformer and has broad application prospects. Since the output of LPCT is generally directly supplied to the electronic circuit, the secondary load is relatively small. The core is usually made of high magnetic conductivity materials such as microcrystalline alloy, which can meet the requirements of measurement accuracy with a small core cross section (core size).
(7) Compact system structure and standardized modeling
The digital electrical measurement system has the characteristics of small volume and light weight, which can be integrated into the intelligent switching equipment system. According to the design concept of substation electromechanical integration, the function combination and equipment layout can be optimized. In high voltage and ultra high voltage substation, the protection device, measurement and control device, fault recording and other automatic device I/O unit as a part of the intelligent equipment, to achieve the IED near process (process-close) design; The protection and monitoring device can be miniaturized, compact and completely installed on the switch cabinet in the middle and low voltage substation.
IEC 61850 establishes the modeling standard of power system and defines the unified and standard information model and information exchange model for substation automation system. Its significance is mainly reflected in realizing the interoperability of intelligent equipment, realizing the information sharing of substation and simplifying the maintenance, configuration and engineering implementation of the system.
IEC 61850 standard
IEC 61850 is a series of standards for substation Communication Networks and Systems developed by the TC57 working Group of the International Electrotechnical Commission. It is the only international standard reference 5 for substation automation system based on network communication platform. It will also become the communication standard for seamless connection of power system from dispatching center to substation, substation and distribution automation. It is also expected to be the industrial control communication standard of general network communication platform.
Compared with the traditional communication protocol system, IEC 61850 has the following outstanding characteristics in technology: 1. 2. Use distribution and stratification system; 3. Use abstract Communication service Interface (ACSI), special communication service mapping SCSM; 4 Use the Manufacture Message Specification (MMS) technology. 5. Interoperability; Have a future-oriented, open architecture.
Four, conclusion
The application of substation automation system in China has achieved remarkable results, which plays an important role in improving the safety and economic operation level of power grid. At present, with the continuous development of new technology, digital substation is rising. Compared with traditional substation, digital substation has the following advantages: Reduce secondary wiring, improve measurement accuracy, improve the reliability of signal transmission, avoid electromagnetic compatibility, transmission cable grounding overvoltage and two problems, solve the problem of interoperability between devices, the functions of substation can be Shared and unified information platform, to avoid repeated equipment, automatic operation and further improve the management level. Digital substation is the development direction of substation automation technology.
