Application of Embedded Ethernet in Power High Voltage Monitoring System

Computer communication network is the key to substation automation system. This paper studies the new generation of power high voltage monitoring system based on embedded Ethernet, and gives the network implementation scheme and its functional characteristics. Practice has proved that the new generation of high voltage monitoring system has better interoperability and openness, can meet the needs of future substation automation development, and represents the latest achievements of substation automation development.

1Embedded Ethernet Technology

With the rapid development of the Internet, Ethernet communication technology has been more and more widely used. Embedded Ethernet has been widely used in the field of embedded control due to its fast speed, wide bandwidth, good interoperability, strong scalability and low price. The use of embedded Ethernet technology in substation automation system represents the latest development direction of substation automation network technology.

The level of embedded microprocessors, main frequency speed, and control software for smart devices have been greatly improved. Coupled with the rapid popularization of the Internet, these new achievements in computer development have strongly promoted the widespread application of embedded Ethernet network technology in the control field. The IEC International Standardization Organization, which represents the advanced field of the development of world power standards, has formulated the network communication system IEC61850 for substation automation systems to make the automation products of different manufacturers interoperable. Although the official version of the standard has not yet been promulgated, the IEC61850 committee draft that has been published has clearly defined embedded Ethernet network communication technology as the only communication network in the field of substation automation, which will be an international trend in technology development.

2. Network architecture of high voltage monitoring

The networking mode of high-voltage monitoring system based on Ethernet can be very flexible. In the automation system of small substation, a simple star network topology can be adopted, and each intelligent device is directly connected to the main control communication unit through Ethernet.

The IEC61850 Substation Communication Network and System standard recommends that the automation system of large and medium-sized substations should adopt an interval-configured, object-oriented networking method, as shown in Figure 1. The network system is roughly divided into three layers.

The top layer is the station control layer. It includes dual master control communication units, which are in redundant hot standby mode. The master control communication unit is responsible for managing the intelligent communication units in the entire station, collecting data from each intelligent unit and sending it to the dispatching master station, and distributing the control commands issued by the master station to the corresponding acquisition units; the dual-machine database is refreshed synchronously through the network; its backup mode can be either master-slave mode or parallel operation. According to user needs, advanced application management units can be configured on the network, such as local functions, reactive power integrated control server, non-protection control server, backup power automatic switching server and other advanced application functions. These advanced application management units can be concentrated in the master control communication unit in the form of dedicated software modules (except local functions), or distributed to other nodes of the network to realize corresponding management functions.

The middle layer is the interval communication unit. It is responsible for managing and collecting data from the intelligent devices in this interval and sending it to the station control layer; receiving control commands from the station control layer and distributing them to the corresponding intelligent devices. At the same time, it can complete the automatic control functions in this interval through the corresponding software modules. The interval communication unit can also be configured as a dual-machine hot standby mode according to user needs.

The intelligent unit includes a measurement and control module and a protection module, which respectively complete the measurement and control function and the protection function.

The main control communication unit and the interval communication unit adopt a dual-network shunting and fault switching communication mode. During normal communication, the dual networks transmit different data contents respectively. Once one of the networks fails, the other network will take on the function of transmitting all data. This not only improves the real-time performance of the system, but also greatly improves the reliability of the system.

The interval communication unit transmits real-time data to each intelligent device via 10Mbit/s Ethernet. Since there are relatively few devices in this network segment, the real-time nature of the data can be fully guaranteed.

Reasonable network configuration can reduce network conflicts and improve the real-time performance and reliability of the system.

3 Implementation of Network Communication Protocol

Network communication protocol is the basis of equipment interoperability. At present, there is no international standard that can be directly followed in the field of substation automation. IEC61850 is undoubtedly the development direction of network communication architecture in the future, but the formulation and promulgation of international standards will still take some time. In the formulation of network communication protocol, we adopted the basic design specifications of IEC61850, that is, the device-oriented and object-oriented network architecture.

As shown in Figure 2, the network communication protocol is based on the TCP/IP protocol and is divided into a three-layer architecture.

The communication service layer is built on top of TCP/IP to complete the establishment and maintenance of communication links. The communication service layer provides reliable end-to-end communication services to the upper layer.

The service primitive layer converts the primitive calls of the protocol layer into network message structures, and sends the data out through the communication service layer. Under the network architecture of heterogeneous machines, the mutual conversion between the host byte order and the network byte order of the data message is completed. This protocol supports service primitives consistent with IEC61850. The basic service primitives supported are: the data object service layer calls the corresponding service primitives to complete the synchronous refresh between the client and server databases, device management, directory services and other application-oriented functions. The object service adopts the client/server model. This network protocol supports a variety of data objects. Each data object defines two parts: object value and object attribute. Data objects include real-time data objects, event data objects, control objects, file objects and other categories.

4Embedded Network Management

In the power system, substations are numerous and wide-ranging. At the same time, in order to meet the requirements of reducing staff and increasing efficiency and modern management, a large part of substations are unmanned substations, which requires that the substation automation system should have extremely high reliability and maintainability. With the in-depth development of computer Internet and the construction of the national power data network, interconnecting automation systems at all levels through the Internet will become a new development trend. It also provides good conditions for device configuration management technology based on embedded web servers.

The new high-voltage monitoring system supports web-based equipment management. Authorized users can use standard web browsers (such as IE) on the client side to easily and quickly configure and manage equipment and access network information at any node of the network (even the Internet). It realizes online management of substation equipment and real-time monitoring of collected data. When the substation operating equipment is abnormal, it can automatically send emails or mobile phone short messages and other alarm information to designated users according to the user's settings, and promptly notify the management personnel to handle the equipment failure. During normal operation, it can also automatically send equipment operation logs to designated email mailboxes regularly according to the user's settings.

The web-based equipment management method greatly reduces the labor of equipment operators, enables equipment management departments to timely understand substation operation information, and handle equipment failures more quickly and effectively. With the development of the national power data network, web-based equipment maintenance will be more superior than the previous maintenance method based on remote dialing.

5Embedded automatic control

With the development of computer technology and communication network technology, the processing power of intelligent equipment used in substation automation is getting stronger and stronger, and the network speed is getting faster and faster. The automatic functions that originally required some independent devices to complete can now be distributed to various intelligent devices in the new monitoring system. The development direction of substation automation is bound to be towards a fully distributed system.

Through the powerful and efficient Ethernet communication network, information sharing can be easily achieved between various intelligent devices. The new monitoring system fully supports the five programmable logic control languages ​​defined by IEC61131-3. Users define their own logic to realize various automatic control functions. Through configuration information, the automatic control functions can be distributed to various intelligent devices, thus realizing truly distributed automatic control functions. Such as distributed reactive power integrated control, distributed small current grounding line selection, distributed power supply standby automatic investment and other automation functions.

6 Conclusion

The new generation of high-voltage monitoring system adopts internationally advanced substation technology and computer network communication technology, and actively approaches IEC international standards, making the system have good interoperability and openness. The use of embedded Ethernet technology has greatly improved the real-time and reliability of the system, and has good expandability and easy-to-use characteristics, which can meet the needs of future substation automation development. It represents the latest achievements in substation automation development.