Abstract: The gradual development of smart substation technology makes the importance of Ethernet switch in substation increasingly obvious. The article first introduces the Ethernet frame in the switch learning and forwarding principle, and then shows the substation hierarchical structure of the secondary system using switches networking solutions, and then detailed analysis of vlan, qos, mirroring, multicast and other switching technology principles According to the characteristics of various IEDs and the characteristics of data streams, practical solutions for each technology are given. According to different business needs and different types of packets, the design of a reasonable network topology, and the flexible use of these switching technologies can protect the smart substation communication packets in a safe, stable and reliable transmission, making the entire substation becomes stronger .
introduction
With the development of information communication and computer network technology, as well as the development of intelligent circuit breakers and new transformer technology, smart substation has become the hotspot of research. Intelligent substation is the use of advanced and stable intelligent equipment to complete the digital information, communication platform network, the standardization of information sharing as the basic requirements of the automatic acquisition of information, measurement, control, protection, measurement and monitoring of basic functions, according to Need to support the real-time automatic control of the power grid, intelligent regulation, online analysis and decision-making, collaborative interaction and other advanced features to achieve adjacent substations, grid dispatching and other interactive substations [1-5]. Thus, the communication network is the key to substation intelligence, and Ethernet switches are the hub of the entire network. The article introduces Ethernet switching principle and its application in intelligent substation.
1 exchange principle
A switch is a device that connects various types of servers and terminals and is responsible for receiving and forwarding data between them. , Which detects the MAC (Media Access Layer) address of the source and destination of the packet from the Ethernet port and then compares it with the internal MAC table of the system. If the MAC layer address of the packet is not in the lookup table, it is added Find the table and send the data packet to all the ports; if the address is in the table, it will be sent to the corresponding port; if the destination address corresponds to the port, it will not be forwarded.
Based on the above principle, the switch to complete the following functions:
Address learning: The Ethernet switch learns the MAC address of all the devices connected to its port. The process of address learning is to monitor the source MAC address of all the incoming data frames by monitoring all the incoming data frames, form a mapping of MAC addresses to their corresponding ports, and store the mapping in the MAC address table in the switch cache.
Forward / filter decision: When a data frame arrives at the switch, the switch first looks up the MAC address table to decide how to forward the data frame. If the destination address is mapped in the MAC address table, it is forwarded to the port connecting to the destination node. Otherwise, the data frame is forwarded to all the ports except the source port.
Loop avoidance: When the switch includes a redundant loop, the Ethernet switch avoids loop generation through a ring protocol (such as rstp) to prevent data frames from continuously circling in the network, and allows the existence of backup path.
2 switches in the smart substation network
In IEC61850 the substation is divided into three layers: station control layer, interval layer and process layer. Network structure is as follows:
FIG simply the network structure in an interval, wherein the control station comprises a monitoring background layer, fault information system, workstation engineers; Q comprises a protective barrier, oscillograph, measurement and control devices; intelligent circuit breaker comprises a process layer, electron formula Transformer, smart terminal, merging unit. The three-tier equipment is interconnected by two networks, namely, a station control layer network that connects the station control layer and the bay layer, a process network that contacts the bay layer and the process layer, transmits protection action events on the station control layer network, Record wave files, four remote information, etc., in the process of network transmission protection tripping, protection start, protection block, circuit breaker position, sampling and other real-time information [1-5].
3 common exchange technology
3.1vlan
Virtual Local Area Network (VLAN) is a technology that implements virtual workgroups by logically and not physically dividing devices within a LAN into subnets. VLAN technology allows network managers to logically divide a physical LAN into different broadcast domains (or virtual LANs), each containing a set of computer workstations that share the same requirements, with physically formed LANs Same attribute However, since it is logical and not physically divided, it is not necessary for the individual workstations in the same VLAN to be placed in the same physical space, that is, the workstations do not necessarily belong to the same physical LAN segment. Broadcast and unicast traffic within a VLAN is not forwarded to other VLANs, helping to control traffic, reduce equipment investment, simplify network management, and improve network security.
In the smart substation, according to different voltage levels are divided into different logical regions, such as 220kv system area, 110kv system area, 35kv system area. Within different voltage levels, vlan is divided according to the interval, and a vlan is divided every interval [4-7]. Such as 220kv system, intelligent terminals, merging unit with the corresponding line protection or bus protection in the same vlan, 35kv system, intelligent terminal, merging unit with the corresponding protection and monitoring integrated device or the same vlan.
In the substation network will encounter an IED and multiple vlan IED communication, this time, to use the switch vlan intersection function, or hybrid vlan mode. As usual bus protection to communicate with multiple IED vlan, the background to communicate with multiple bay devices, in these cases to set vlan intersection.
3.2 image technology
Port mirroring A method of mirroring data on one or more ports of a switch to one or more ports. In some switches, we can configure the switch to copy data packets from one port to another. This process is "port mirroring".
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