Virtual local area network VLAN (Virtual LocalArea Networ) technology fully reflects the important characteristics of modern network technology: high speed, flexibility, easy management and easy expansion. Whether it has VLAN function is an important indicator to measure LAN switches, and network virtualization is also the trend of future network development. VLAN technology is a technology to form a virtual working group by logically dividing the devices in the LAN into different network segments, to reduce collisions and broadcast storms, enhance network security, and lay the technical foundation for the realization of the 802.1p protocol. Provided means of implementation.
The switch occupies an absolute position in the network, so in a sense, the performance and cost of the switch determine the performance and cost of the network. Currently, 10 / 100M adaptive network switches are the mainstream in the market, and 1000M network switches have not been widely promoted due to cost reasons. The amount of network information data in the process layer of the intelligent substation is considerable, but most of the information data does not need to circulate horizontally. The VLAN networking technology is used in the process layer network to lay the foundation for the application of 100M Ethernet switches in the network of the intelligent substation With the theoretical foundation, it not only reduces the cost of networking, but also satisfies the network security and reliability.
1 Communication requirements of digital substation
The IEC61850 standard distributes the substation automation system logically into three layers (station layer, bay layer, process layer). The logical relationship between these layers and logical interfaces is shown in Figure 1.
According to the IEC61850-7-1 standard, the process layer and the spacing layer use the IEC61850-9-1 / 2 protocol and the GOOSE protocol for communication, and the spacing layer device and the station control layer use the IEC61850-8-1 (MMS) communication. IEC61850-9-1 adopts point-to-point transmission mode, only need to consider the bandwidth of the transmission medium and the ability of the receiving CPU to process data, without worrying about the impact of data traffic on the transmission of other interval equipment, because it does not share the network with other intervals through the network Bandwidth, so no switch is required. This method is simple and reliable, but the fiber connection is complicated, and cross-interval protection cannot be achieved within the standard range, and the installation method is not flexible. The IEC61850-9-2 method connects the sampler data signal of the merger to the process layer network through optical fiber. The equipment such as bay layer protection, measurement and control, and measurement are no longer directly connected to the merger. Information data is obtained through the process layer network to achieve sampling. Signal information sharing. By adopting network priority technology, VLAN technology, multicast technology and other network technologies in the switching network, it can effectively prevent the flow and speed of sampled value transmission from affecting the process layer network, and ensure that the process layer data is safe, efficient and orderly on 100M Ethernet transmission.
The IEC61850-3 part defines the communication and related system requirements between intelligent electronic equipment (IED) in the substation automation system (SAS), and the reliability, availability, maintainability, and safety of the communication system for monitoring, configuration, and control of equipment in the station Performance, data integrity and other performance requirements. In order to meet these requirements, communication between devices depends on 100-Mbit / s fiber Ethernet based on the IEC61850 standard. Process-level devices are interconnected through a process-level bus, and bay-level devices are interconnected through a station-level bus.
The network switch requires the following management functions:
Reliability meets IEC61850-3 standard
The switch supports multi-ring networking solutions
High-speed eRSTP ring network redundancy technology, the recovery time of each switch is "5ms
Zero-Packet-Loss zero packet loss technology
Wide temperature range
Super anti-electromagnetic interference ability
MTBF is long, ensuring high availability
Support 802.1QVLANs
Support 802.1p protocol
2 Single interval transmission traffic calculation and VLAN solution
2.1 Transmission flow calculation
Because part of the information needs to be shared between different intervals, not all the information, the whole-station process layer switches are cascaded in a star mode through the backbone switches, as shown in Figure 2. If you do not perform flow control on the outgoing data of the switch at the bay layer, it is easy for the backbone network switch to flow into the overload situation, causing the network to be blocked or even paralyzed. We conducted theoretical calculations and actual tests on SMV data traffic and GOOSE data traffic at a single interval, and the results were basically the same.
The actual maximum packet length in the IEC61850-9-2 project (SVLD is a variable length), single-interval SMV theoretical calculation flow: calculated at 1 point per frame (12 analog channels), a merger per second data flow :
S = 159 bytes & TImes; 8bit / byte & TImes; 50 cycles / s & TImes; 80 points / cycle = 5.088Mbit / s;
The actual test SMV flow rate in a single interval is comparable to the theoretical calculation data.
Actual maximum message length in GOOSE project:
According to T0 = 10s calculation, the data flow per second of an intelligent device:
S = 6016 bytes & TImes; 8bit / byte × (1s / 10) frame = 0.048Mbit / s;
The total data throughput of the switch is determined by the data flowing into the switch. In theory, the incoming data can flow out correctly, but the size of the data traffic determines the network (latency) performance. The data flowing into the backbone network switches is mainly the data required for cross-interval protection, such as data required for failure protection, bus protection, etc. Estimate according to unit interval, such as protection current in SMV data, GOOSE data, etc. Since the GOOSE information traffic is negligible compared with SMV, the data flowing into the backbone switch is equivalent to one-third of the interval switch. According to the theoretical calculation, the data is 1.6Mbit / s. Therefore, in addition to the number of exchange ports to meet the project selection, the backbone network switches can also meet the capacity requirements for general-sized intelligent substations.
2.2 VLAN solution
The above has made it clear that the data that needs to be transmitted horizontally on the network is not all data, but is a part of cross-interval protection or other devices. Therefore, a VLAN scheme must be adopted, that is, the 802.1p protocol allows it to pass the data required horizontally. The data used across the interval can be circulated vertically in this interval. Secondly, data circulation needs to be prioritized. The IEC61850 specification divides the data on the network in the substation in detail, and gives different priorities to different packets according to the different needs and requirements of the network information.
2.2.1 Several modes of VLAN division
Port-based VLAN
MAC address based VLAN
Route-based VLAN
Policy-based VLAN
The port-based VLAN division mode is the simplest and most effective method, and it has been fully and effectively applied in the intelligent substation network. The port-based VLAN mode logically divides the switch into different virtual local area networks according to the ports, so that it can circulate on the required local area network.
2.2.2 Principles of process layer network VLAN division
For the processing of sampled values:
The current combiner and its corresponding devices should be divided into a VLAN and the site is unique; the current combiner should be divided into a VLAN and all the devices on the bus where it needs voltage to be a VLAN and the site is unique.
Processing of GOOSE information:
Adopt IEC61850-9-2 to assign a VLAN to the GOOSE information of the whole station, and the whole station is unique. When using the IEC61950-9-2 method, considering the comparison with the sampled value, GOOSE has very little information, and if it is not divided into VLANs, it will not affect the network performance too much.
Time message processing:
Allocate a VLAN uniformly, the default is VLAN1.
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