Network communication mode of digital substation

0 Preface

Substation automation technology has reached a certain level after more than ten years of development. In China's urban and rural power grid transformation and construction, most substations have adopted integrated automation technology, which has achieved unattended duty, thereby reducing the total cost of construction and operation of substation construction. , Greatly improving the modernization level of power grid construction. With the gradual maturity of technologies such as intelligent switches, photoelectric transformers, and online status detection of one-time operation equipment, and the development and application of computer high-speed networks in real-time systems, fully digital substation automation systems have emerged.

At present, with the development of high-voltage and ultra-high-voltage systems, higher requirements are placed on the safety, stability, reliability, control, and information exchange of the power grid. State Grid Corporation included "Digital Substation Technology" as one of the five major topics in power grid automation technology in the State Grid Corporation's "Eleventh Five-Year" Technology Development Plan. Digital substation technology is the future development direction of substation integrated automation technology.

1 Characteristics of digital substation

The digital substation has the following main features:

(1) Digitalization and intelligence of primary equipment

Electronic or photoelectric transformers replace the traditional electromagnetic transformers in substations, which can directly provide digital optical fiber Ethernet interfaces to the outside; smart circuit breakers, transformers and other equipment with digital communication to the outside are used in the station, or in These primary equipments are equipped with on-site intelligent terminals to realize digital conversion and status monitoring of signals, so as to meet the requirements of primary equipment digitization and intelligence.

(2) Digitization and networking of secondary equipment

In addition to the characteristics of general digital equipment, the secondary equipment of digital substations also has external fiber optic network communication interfaces. Unlike the traditional substation information transmission, which uses cable as the medium, the secondary signal transmission of digital substations is based on fiber optic Ethernet.

(3) Substation communication network and system realize IEC61850 standardization

The difference between the information description and network communication protocol standards in traditional substations leads to the difficulty of signal identification and poor interoperability between different devices; the digital substation full station communication network and system implementation adopt the IEC61850 standard, which is complete, systematic, and open It ensures that the equipment in the digital substation has the characteristics of interoperability.

(4) Automation of operation management system

On the basis of the existing comprehensive automation system already possessing a greater degree of automation features, the digital substation further reflects the characteristics of operation management automation in the aspects of interoperability of equipment in the station, optical fiber transmission of signals, and information sharing of network communication platforms. In summary, the application of transformers based on photoelectric technology constitutes the digital application of electrical information collection in substations; the promulgation and implementation of the IEC61850 standard lays the foundation for the unified modeling of information in substations; the development of Ethernet technology is based on the realization of The network-based information exchange provides technical support; the development of intelligent circuit breaker technology enables the substation automation technology to extend the application of secondary equipment to primary equipment.

2 Digital substation communication network requirements

2.1 Functional requirements

The fundamental task of the communication network is to solve the real-time information exchange within the integrated automation system and with other systems. The network is an indispensable functional carrier. Building a reliable, real-time, and efficient network system is one of the keys to the communication system. Group 34 (Protection and Control Group) of the 2000 International Power Grid Conference, discussed and introduced substation automation and its communication system. The basic consistent idea is that communication technology is the key to substation automation systems. The communication network is the link connecting various intelligent electronic devices (IED) in the station, so it must be able to support various communication interfaces to meet the standardization of the communication network. With the unmanned substations and the increasing amount of automation information, the communication network must have enough space and speed to store and transmit data such as events, power, operations, faults, and wave recorders. In order to improve the quality of voltage operation, unattended substations require the communication network to have voltage and reactive power automatic adjustment functions, system timing functions, etc. In addition, self-diagnosis, self-recovery, remote diagnosis, and online status detection are several functional requirements for operation and maintenance.

2.2 Performance requirements

The performance requirements of the communication network are mainly reflected in the following aspects:

(1) Reliability Due to the continuity and importance of power production, the reliability of the communication network in the station is of the highest priority, and it should be avoided that individual devices are damaged and the communication in the station is interrupted. With the application of digital and image information multimedia technology, monitoring will rely more on the communication network, so a reliable communication network is the first condition.

(2) The open communication network in the station is a subsystem of dispatch automation. In addition to ensuring the interconnection and easy expansion of the IED equipment in the station, it should also obey the overall design of power dispatch automation. The hardware interface should meet international standards, and international standards should be selected. The communication protocol facilitates user's system integration.

(3) Real-time performance requires real-time transmission due to measurement and control data, protection signals, remote control commands, etc. Although the data flow in the station is not large during normal operation, a large amount of data needs to be transmitted when a failure occurs, and information needs to be quickly transmitted on the communication network within the station .

2.3 Implementation method

(1) Optical fiber network in the substation station The optical fiber network in the substation station realizes full digital optical network communication between the primary and secondary equipment in the station. It mainly includes the digital transmission of secondary transmission equipment such as digital transmission protection of electrical quantity collected value, tripping, status signal and fault alarm signal, and the digital transmission of analog signals such as intelligent transformer alarm signal, tap remote adjustment and temperature.

(2) The unified standard platform of the whole station, unified information module, data model, and functional model, unified communication protocol, seamless data exchange, reliability, integrity, and real-time nature of information transmission. Various devices share unified information and are interoperable. After the combined design of functions, the use of advanced computer technology, modern communication technology and signal processing technology to achieve automatic monitoring, automatic control and protection of main equipment and transmission and distribution lines of the entire substation, and automation of dispatching communication Features.

(3) Digitized / intelligent primary equipment The signal circuit and controlled operation driving circuit of the primary device detection are designed by using microprocessor and photoelectric technology. The conventional relays and logic circuits in the secondary circuit of the substation are programmable controller instead.

(4) Reduce secondary control and signal cables to replace secondary control cables and signal cables bundled outdoors and in control rooms with optical cables and a small number of communication cables. Reduce the area of ​​secondary wiring, reduce the total cost of substations, and reduce operating costs.

(5) The system data is collected in situ. The optical fiber is used to realize the transmission of data signals. The signal collection has high precision and strong reliability. The data signal source is unique, the repeated investment is small, and the layered control and layered data transmission are realized to improve data transmission and application. s efficiency.

3 Communication standard of digital substation

The communication system of the digital substation is based on the IEC61850 standard. IEC61850 provides a series of standards for substation automation system functional modeling, data modeling, communication protocols, communication system project management and consistency testing. Building communication networks and systems for substations in accordance with IEC61850 is an effective way to build digital substations. The release of IEC61850 provides a solid foundation for the construction of digital substations. According to the IEC61850 standard, the functions of substations should be divided into station control layer, bay layer and process layer. The digital substation communication system should have the communication interface shown in Figure 1.

① Communication interface between station control layer equipment; ② communication interface between station control layer and bay layer equipment; ③ communication interface between bay layer equipment; ④ communication interface between bay layer and process layer equipment; ⑤ station control layer equipment and The communication interface of the remote control center; ⑥ the communication interface between the equipment at the distance layer and the remote protection.

The communication interface ③ is implemented on the communication interface ② or ④ according to the situation, and the communication interfaces ① and ② can share a physical communication network in small-scale substations. The communication interfaces ① ~ ④ shall be constructed in accordance with the IEC61850 standard. In order to interface with the existing dispatching system, the communication interface ⑤ still adopts the IEC60870-5-101 or 104 protocol, but the telecontrol communication interface device should have the ability to be upgraded to IEC61850. The communication interface ⑥ is mainly used for longitudinal differential protection, long jump device, etc., defined by the equipment manufacturer, and should be able to be implemented on the communication system between substations.

The physical equipment of the digital substation should be able to exchange information in real time, efficiently and reliably. Ethernet communication technology is the best choice to meet this requirement. According to the experimental reports of IEEE and EPRI, the existing Ethernet communication technology can fully meet the communication requirements of substation automation. Ethernet technology is the mainstream communication technology, with excellent economy, and is still in rapid development, providing a broad development space for substation automation systems.

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