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NETWORK / 24 / JULY/AUGUST 2017 IEC 61850 SolutIonS As a minimum a solution is likely to integrate several intelligent electronic devices (IEDs), such as protection devices, measure- ment centres, bay controllers, etc. communicating with the rest of the system via one or more protocols. Today modern systems can be constructed through an Ethernet network linking components through an appropriate archi- tecture. The Ethernet network might be within a substation, typically for a transmission or distribution application, or it may interconnect dispersed substa- tions such as are commonly found in industrial or infrastruc- ture applications. Deploying a client-server communication exchange can avoid any central point of failure and facilitates a tailored redundancy. For large sites and when many voltage levels are to be considered, multiple-ring Ethernet architectures may be considered to allow an appropri- ate network segmentation. Physical communications between components are based on two main technology families (Ethernet and serial links) in order to cope with various ap- plication performance needs and re-use of existing devices and integration of third-party equip- ment. Solutions that support typi- cal serial protocols (T103, DNP3 and MODBUS, for example) in order to interface existing devices and can be fully integrated into an IEC 61850 system through a gateway device. State-of-the-art communi- cation technology is based on client-server and peer-to-peer links. This relies on fast Ethernet networks and offers new per- spectives in terms of distributed functions, performances and flexibility. It enables innovative automation schemes and flex- ible addition of new applica- tions. Ideally these are based on standard Ethernet communica- tion infrastructures. Switched Ethernet is the preferred choice because it manages collisions over the network. The possible latency time of the network itself becomes negligible with regards to the equipment response time, so the system determin- ism is primarily dependent on the choice of the devices and its architecture. Correct selection of Ether- net switches, robust devices designed for the substation en- vironment will enable various topologies (ring or star or mixed) with the possibility of a redun- dant communication path for increased availability. Ethernet IEC 61850 IEC 61850 is the standard for communication in power systems based on Ethernet and provides fast peer-to-peer and self-descriptive communication between IEDs, up to 100Mbps. It includes general aspects (project management, substation func- tions, and more), detailed data model, configuration language and conformance tests. The IEC 61850 communica- tion can be fully redundant. Time synchronisation is part of this standard and 1ms resolution can be achieved for sequence-of- events analysis (for example). Software modules are avail- able which offer IEC61850 client and server services, meaning that an application can act as a client and/or server. IEC61850 client and server applications may be separate software modules or merged in one. Peer-to-peer communications With new technologies, protec- tion schemes are becoming more complex. Inputs and outputs are traditionally hardwired between different IEDs. During the engineering process, a small change in the protection scheme logic could require a substantial amount of effort to implement, espe- cially during later stages of the engineering process. This change could require updating engineering drawings, making modifications to, or adding new wiring between devices. These changes can be time consuming and labour intensive, requiring different trades to accomplish what could be considered a trivial change to some digital logic. GooSE IEC 61850 generic object-ori- ented substation event (GOOSE) messages are high-speed mes- sages optimised to be multicast over an Ethernet network. These messages allow for digital representations of hardwire I/O to be published on the network and received by the subscribers within a given timeframe. The major benefit of using GOOSE messaging for I/O is that adding new logic variables and virtual inputs and outputs can be simpli- fied, requiring the engineer to modify only the device configura- tions. The potential now exists for much more complex, distributed protection schemes. Removal of physical I/O limita- tions of protection relays allows for many virtual input and output signals – internal to a relay and not typically used in today's schemes – to be shared between multiple devices. In theory it could be several hundreds, in reality there are limitations to be considered. Ethernet architectures An Ethernet network can be over optical fibre and/or copper twisted pair and fully redundant Ethernet solutions can be engineered. Ethernet network redundancy can be realised through ring architecture, redundant star architecture or mixed architectures. PRP (parallel redundant protocol) PRP principle is based on the duplication of the Ethernet net- work infrastructure. Any device is doubly attached to the two LANs. The traffic is duplicated to the two networks. Frames are sent at the same time on the two networks and the first arrival is used the second is discarded. This mecha- nism protects applications from data loss – in case of any failure, there is always one available link to transmit data. The network unavailability time is by construc- tion 0ms. PRP relies on the paral- lel operation of two local area networks (LANs). It allows a mixture of both redundant and non-redundant equipment on the same network. DAnP: doubly attached node PRP DAnP IED DAnP IED DAnP IED Switch lAn B Switch lAn A PC