Development status and trends of integrated substation automation

The substation is an indispensable and important link in the power system. It is responsible for the heavy tasks of power conversion and power redistribution, and plays a decisive role in the economic operation of the power grid. In order to improve the stable operation level of substations, reduce operation and maintenance costs, improve economic benefits, and provide high-quality electric energy services to users, comprehensive automation technology for substations has begun to emerge and has been widely used.

Comprehensive substation automation is to apply computer technology and modern communication technology to the secondary equipment of the substation (including control, signal, measurement, protection, automatic devices and remote control devices, etc.), and implement automatic monitoring and measurement of the substation through functional combination and optimized design control and coordination, as well as comprehensive automation systems such as dispatch communication. Realizing comprehensive automation of substations can improve the economic operation level of the power grid, reduce infrastructure investment, and provide a means to promote unattended substations. The rapid development of computer technology, information technology and network technology has led to the advancement of comprehensive automation technology in substations. In recent years, with the development of digital electrical measurement systems (such as photoelectric transformers or electronic transformers), intelligent electrical equipment and related communication technologies, the integrated automation system of substations is moving towards digitalization.

I. Main functions of substation integrated automation system

The basic functions of the 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 comprehensive control subsystem;

4. Low-frequency load shedding control subsystem of the power system;

5. Standby power supply automatic switching control subsystem;

6. Communication subsystem.

This part is relatively rich in content, and there are many documents that explain it in detail, so this article will not go into detail.

II. Traditional substation automation system

1. System structure

At present, the structures of integrated substation automation systems at home and abroad are classified into the following three types based on design ideas [1]:

(1) Centralized

Use computers of different grades to expand their peripheral interface circuits, centrally collect analog, switching and digital information of the substation, perform centralized processing and calculations, and complete microcomputer monitoring, microcomputer protection and some automatic control functions. Its characteristics are: high computer performance requirements, poor scalability and maintainability, and suitable for medium and small substations.

(2) Distributed

Divided according to the monitored objects or system functions of the substation, multiple CPUs work in parallel, and network technology or serial methods are used to implement data communication between CPUs. The distributed system is easy to expand and maintain, and local failures do not affect the normal operation of other modules. This mode can be used for centralized screen grouping or split-screen grouping during installation.

(3) Decentralized distribution

Each data acquisition, control unit (I/O unit) and protection unit in the bay layer are installed locally on the switch cabinet or near other equipment. Each unit is independent of each other and is only interconnected through the communication network and is connected to the main substation-level measurement and control unit. communication. Functions that can be completed at the bay level do not depend on the communication network, such as protection functions. The communication network is usually optical fiber or twisted pair, which compresses secondary equipment and secondary cables to the maximum extent, saving engineering construction investment. The installation can either be dispersed in each compartment, or it can be centralized or hierarchical grouping of screens in the control room. It can also be that one part is in the control room and the other part is scattered on the switch cabinet.

2.Existing problems

The substation integrated automation system has achieved good application results, but there are also shortcomings, mainly reflected in: 1. The information exchange between primary and secondary still continues the traditional cable wiring mode, which is high cost and inconvenient in construction and maintenance; 2. The secondary data collection part is largely repeated, which wastes resources; 3. Information standardization is insufficient, information sharing is low, multiple systems coexist, and interconnection between devices and between devices and systems is difficult, forming information islands and making it difficult for information to be comprehensively applied; 4. When an accident occurs, a large amount of event alarm information will appear, lacking an effective filtering mechanism, which interferes with the correct judgment of the fault by the on-duty operators.

III. Digital substation

Digital substations are the next stage in the development of substation automation. The "Power Grid Company's "Eleventh Five-Year Plan" Science and Technology Development Plan" has clearly stated that during the "Eleventh Five-Year Plan" period, digital substations will be studied and demonstration stations will be built. 2, and there are currently digital substations. Completed and put into operation, such as Fuzhou Convention and Exhibition Transformation 110 kV digital substation.

1. Concept of digital substation

Digital substation refers to a substation in which the information collection, transmission, processing, and output processes are completely digital. Its basic characteristics are intelligent equipment, communication network, and automated operation and management.

Digital substations have the following main features:

(1) Intelligent primary equipment

Intelligent primary equipment such as electronic transformers and intelligent switches (or traditional switches with intelligent terminals) using digital output. The primary device and the secondary device exchange sampling values, status quantities, control commands and other information through optical fiber transmission of digitally encoded information.

(2) Secondary equipment networking

The communication network is used to exchange information such as analog values, switching values, and control commands between secondary devices, and control cables are eliminated.

(3) Operation management system automation

Automation systems such as automatic fault analysis systems, equipment health status monitoring systems and programmed control systems 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 substations

(1) Digitization of data collection

The main sign of a digital substation is the use of digital electrical measurement systems (such as photoelectric transformers or electronic transformers) to collect electrical parameters such as current and voltage 3 to achieve effective electrical isolation of primary and secondary systems and increase It increases the dynamic measurement range of electrical quantities and improves the measurement accuracy, thus providing a basis for realizing the transformation from conventional substation device redundancy to information redundancy and the application of information integration.

(2) System hierarchical distribution

The development of substation automation systems has experienced a transition from centralized to distributed. Most of the second-generation hierarchical distributed substation automation systems use mature network communication technology and open interconnection protocols, which can record equipment information more completely and significantly Improve system response speed. The structure of the digital substation automation system can be physically divided into two categories, namely intelligent primary equipment and networked secondary equipment; in terms of logical structure, it can be divided into "process layer" and "bay layer" according to the definition of IEC61850 communication standard. "," station control layer" three levels. High-speed network communication is used within and between each level.

(3) Networking of information interaction and integration of information applications

Digital substations use low-power, digital new transformers instead of conventional transformers to directly convert high voltage and high current into digital signals. Information exchange occurs between devices in the site through high-speed networks. Secondary devices do not have I/O interfaces with duplicate functions. Conventional functional devices become logical functional modules to achieve data and resource sharing. At present, IEC61850 has been determined internationally as the substation automation communication standard.

In addition, the digital substation integrates information and optimizes the functions of the original scattered secondary system devices, so it can effectively avoid the duplication of hardware configurations in the monitoring, control, protection, fault recording, measurement and metering devices of conventional substations problems such as non-sharing of information and high investment costs occur.

(4) Intelligent equipment operation

The new high-voltage circuit breaker secondary system is established using microcomputers, power electronics technology and new sensors. The intelligence of the circuit breaker system is realized by the microcomputer-controlled secondary system, IED and corresponding intelligent software. Protection and control commands can be passed. The fiber optic network reaches the secondary circuit system of the unconventional substation, enabling a digital interface with the circuit breaker operating mechanism.

(5) Equipment maintenance status

In digital substations, power grid operating status data and fault and action information of various IED devices can be effectively obtained to achieve effective monitoring of operation and signal loop status. There are almost no unmonitored functional units in digital substations, and there are no blind spots in the collection of equipment status characteristics. The equipment maintenance strategy can be changed from "regular maintenance" of conventional substation equipment to "conditional maintenance", thus greatly improving the availability of the system.

(6) The measurement principle of LPCT and the appearance of the inspection instrument

As mentioned before, LPCT is actually an electromagnetic current transformer with low power output characteristics. In the IEC standard, it is listed as an implementation form of electronic current transformer, representing electromagnetic current transformer. A development direction with broad application prospects. Since the output of LPCT is generally provided directly to electronic circuits, the secondary load is relatively small; its core is generally made of highly magnetically permeable materials such as microcrystalline alloy, and the measurement accuracy can be met with a smaller core cross-section (core size). requirements.

(7) System structure compaction and modeling standardization

The digital electrical measurement system has the characteristics of small size and light weight. It can be integrated into the intelligent switchgear system, and the functional combination and equipment layout can be optimized according to the mechatronics design concept of the substation. In high-voltage and ultra-high-voltage substations, the I/O units of protection devices, measurement and control devices, fault recorders and other automatic devices are part of primary intelligent equipment, realizing the process-close design of IEDs; in medium and low-voltage substations The protection and monitoring devices can be miniaturized, compact and completely installed on the switch cabinet.

IEC61850 establishes the modeling standard for power systems and defines a unified and standard information model and information exchange model for substation automation systems. Its significance is mainly reflected in realizing the interoperability of intelligent devices, realizing information sharing in substations and simplifying system maintenance  configuration and project implementation.

3.IEC61850 standard

IEC61850 is a series of standards for "Substation Communication Networks and Systems" formulated by the International Electrotechnical Commission's TC57 working group. It is an international standard reference for substation automation systems based on network communication platforms. It will also become a standard for power systems from dispatch centers to substations, within substations, and distribution systems. The communication standard for seamless connection of electrical automation is also expected to become the industrial control communication standard for universal network communication platform.

Compared with the traditional communication protocol system, technically IEC61850 has the following outstanding features: 1. Use object-oriented modeling technology; 2. Use distributed and layered systems; 3. Use Abstract Communication Service Interface (ACSI) and special communication service mapping SCSM technology; 4 uses MMS (Manufacture Message Specification) technology; 5 has interoperability; 6 has a future-oriented, open architecture.

VI. Conclusion

The application of substation automation systems in our country has achieved very significant results and plays an important role in improving the economic operation level of the power grid. Currently, with the continuous development of new technologies, digital substations are emerging. Compared with traditional substations, digital substations have the following advantages: reducing secondary wiring, improving measurement accuracy, improving signal transmission reliability, avoiding problems such as electromagnetic compatibility, transmission overvoltage and two-point grounding caused by cables, and solving problems between equipment. Interoperability issues, various functions of the substation can share a unified information platform, avoiding duplication of equipment, and further improving the level of automated operation and management. Digital substation is the development direction of substation automation technology.

Weshine Electric Manufacturing Co., Ltd.