1.1 Information hierarchy of digital substation
The IEC 61850 standard is the most complete communication standard in the field of substation automation. The standard divides the substation automation system into three levels, namely the station control layer, the bay level and the process layer. The station control layer includes monitoring host, operator workstation, telecontrol workstation, engineer workstation, GPS timing device, etc., forming a total station monitoring and management center. The spacer layer includes secondary devices such as relay protection devices and measurement and control devices. The process layer includes primary equipment such as transformers, circuit breakers, disconnectors, transformers, and the like, and the intelligent components to which they belong. As shown in Figure 1-1.
Compared with traditional substations, digital substations have undergone great changes in the process layer. A large number of intricate cables that carry analog and digital inputs are replaced by switches and network cables, and the interaction of information has changed from a hard-wired approach to a network-based approach. Conventional voltage transformers and current transformers are replaced by electronic transformers.
Figure 1-1 Digital Substation Information Hierarchy
1.2 Process layer network implementation technology
Most of the data transmitted on the process layer network is multicast. If the multicast is not filtered, the switch will treat it like broadcast. Therefore, we need to effectively manage and filter multicast to reduce the network. Load, improve network efficiency, reduce latency on the network, and more. The general methods for the switch to manage and filter multicast are VLAN, GMRP, IGMP Snooping, CGMP, and so on. Since GOOSE messages and SV messages are not IP multicast, they are only Layer 2 MAC multicast, so IGMP Snooping and CGMP are not particularly applicable. Therefore, there are currently three main ways to manage and filter multicast in a substation, namely VLAN, GMRP and static multicast address table. Virtual LAN VLAN technology is currently the most commonly used networking technology. I believe many people have an understanding of this technology. Today we focus on the application of GMRP in networking.
1.3 Multicast Management Protocol GMRP
GMRP Dynamic Multicast Management Protocol. GMRP (GMRP MulTIcast RegistraTIon Protocol) Multicast Registration Association
It is part of the Common Attribute Registration Protocol (GARP) and is used to maintain dynamic multicast registration information in the switch. All switches that support the GMRP feature can accept dynamic multicast registration information from other switches to dynamically update the local multicast registration information. At the same time, the multicast registration information of the local device can be propagated to other switches, so that the multicast information of all devices supporting the GMRP feature in the same subnet is agreed. The multicast registration information propagated by the GMRP includes both the static multicast registration information manually configured on the local switch and the multicast registration information registered by the other switch to the local switch.
1.4 Working Process of GMRP Protocol
When a device wants to join a multicast group, it first sends a GMRP join message. The switch adds the GMRP join message to the multicast group and broadcasts the GMRP join message in the VLAN. The multicast source knows the existence of multicast members. When a multicast source sends a multicast packet to a multicast group, the switch forwards the packet to the port that was previously added to the multicast group to implement secondary multicast in the VLAN. As shown in Figure 1-2.
In addition, the switch periodically sends GMRP queries. If the device wants to stay in the multicast group, it will respond to the GMRP query. In this case, the switch does not perform any operation. If the device does not want to stay in the multicast group, it It can send a leave message or not respond to the GMRP query. Once the switch receives the device's leave message or does not receive a response message during the timer setting, it deletes the device from the multicast group.
Figure 1? 2 GMRP basic principles
The protocol is particularly suitable for IEC 61850 9-2 sampled values ​​and GOOSE information transmission based on a subscription/release mechanism in a smart substation process layer network. Compared with VLANs, GMRP does not need to configure the switch cumbersomely (only the switch needs to enable GMRP function), which facilitates the reconstruction and expansion of the substation, which effectively reduces the difficulty of operation and maintenance. However, support for the device NIC driver is required.
1.5 GMRP application in DT6000E optical digital tester
Zhou Ligong Zhiyuan Electronics' optical digital tester DT6000E, the application software has an independent GMRP function, which can send any type of GMRP message and can parse the received GMRP message.
The GMRP module is divided into registration, transmission test and reception test pages on the DT6000E device.
1.5.1 GMRP registration
GMRP registration is that the device sends a JOIN IN message to the switch. The user can add a modified multicast address, select the sending port, and change the sending interval (500s-60000s). The data sent from the tester will only be forwarded by the switch. Give other devices in the same group, and devices that are not added to the group will not receive the data sent by the tester. Click “Turn on GMRP†as shown in Figure 1-3. The device starts to send GMRP packets.
Figure 1-3 GMRP registration page
1.5.2 GMRP send test
The GMRP send test is similar to GMRP registration, except that the test can send any type of GMRP.
The message, and the minimum interval of the message transmission interval is reduced from the original 500s to 1s.
1.5.3 GMRP reception
The Receive Test page is used to receive GMRP packets sent from other devices. The interface enumerates the message type, and
Multicast address. And the content of the message can also be resolved. As shown in Figure 1-4:
Figure 1-4 GMRP message receiving and parsing
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