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The concept of substation is undergoing a paradigm shift: from being a pure “energy hub”

to an “information hub”. Apart from delivering energy to a large grid at a certain voltage level, the substation also monitors, protects and controls the grid – many control operations from the grid control center today are focused on substations. Therefore, in the wake of this tectonic shift in concept, the substation today may more aptly be defined as “a subsidiary station of an electricity generation, transmission and distribution system providing monitoring and protection of the associated grid, and functioning as the main connection point for grid control and monitoring functions”.

While substations are evolving around the concept of centralized protection and control functionalities, it is important to note that bay-level protection and control IEDs are not replaced by those functionalities. In fact, protection and control terminals are still seen as the backbone of the secondary system and they handle time-critical basic protection functions along with communicating with a centralized system. Station level primarily handles all advanced functionalities. As the primary protection is covered by the bay-level IEDs, the functionality in the station level can be updated through the cloud without affecting the safety of the network, thus allowing fast, dynamic and smooth updates. The station level holds two important functionalities of its own: a) time-critical protection functionality, which needs real-time process data and directly affects network safety, and b) offline

functionality to operate on historic information. This function indirectly affects grid safety via condition monitoring and fault analysis functions.

Ethernet network switchesEmerging evolution in networking communication equipments is leading to improvised network performance and reduced downtime across the substation network system. This will result in less outage for customers and therefore greater customer satisfaction and improved revenues for utilities. The good news is that these technologies are available today, and even if they all are not used today, they provide us an excellent migration path to new applications in modernizing substations. The first option to improving network performance is to use Ethernet network switches that are capable of gigabit speeds. Gigabit speeds are not new in enterprise networks parlance but so far they were not widely deployed in substation networks. This is simply because the protection and control equipment has, so far, not required at high levels of bandwidth to perform their functions. Remember that Ethernet networks have been deployed in the substations for only past fifteen years or so but large-scale deployments of Ethernet network has started in the substation communication arena only in recent times, so the need for increased bandwidth across the network is going to be more critical with the passage of time. The next stage in creating digital substation, by using IEC 61850 design, has the potential to

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demand more network bandwidth and lower network latency. Moreover, substation network may also be utilized for other applications using high amounts of bandwidth such as condition based monitoring, new types of emerging field sensors, and security via IP video surveillance systems.

IEC 61850 utilizes layer 2 multicasts for different protocols and applications such as GOOSE messaging, IEEE 1588 time synchronization and Sampled Measured Values (SMV) on the process bus. Multicast is a networking feature that allows a layer 2 message from a single source to be propagated to multiple receivers on the network. It is implemented across the network through the managed network switches that receive the multicast message on one port and flood the message out on desired egress ports. This, in turn, gets propagated to all switches and nodes in the network that want to subscribe to

that data traffic. Multicast messaging therefore needs to be managed by using either some or all available technologies including VLANs to segregate multicast domains, dynamic multicast filtering or providing increased available bandwidth. Gigabit speed switches capable of managing multicast should be used in substations to suffice the requirements of IEC 61850 networks. Packets that are forwarded through network switches are clocked out serially over the Ethernet network. Since gigabit switches clock the message out at 10 times the speed of 100mbps switches the latency time can be significantly reduced.

Properly designed networks - using high speed gigabit, managing multicast with VLANs and dynamic multicast filtering - are essential to prevent network flooding, congestion and dropped packets along with ensuring proper operation of protection and control algorithms. Communication through Layer2 Gigabit

Conceptual Architecture of a Future Substation

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switches can also reduce network communication latency ensuring time sensitive messages are received on time and additionally can provide the capacity to support other substation applications such as physical security. Another important required feature of network switches in the substation communication is ‘field replaceable modules’ which significantly reduces mean-time-to-repair (MTTR) by allowing technicians to repair a problem by swapping out a faulty module with a working spare without having to remove the whole unit.

Communication TechnologiesModular switch design with field replaceable hardware modules also facilitates future upgrades. Communication technology is developing at very fast pace, new applications may require new protocols and new physical interfaces which may not be always feasible to be updated by software or firmware upgrades. So, a hardware design allowing interchangeable module will surely help in future-proofing the network and thereby protecting the CAPEX. Keeping in mind the flexible application perspective of substation automation system - e.g. new communication standard or new physical interfaces like different type of connectors, modulation, sampling rate etc – network equipment manufacturers are expected to develop new communication line module compatible with the network chassis and the device backplane. Thus an upgrade or migration to a new technology would be possible by exchanging or adding newly developed modules without the need to replace the entire network infrastructure in the substation. Such flexibility of the networking hardware can significantly extend the life cycle of a substation automation system. Redundant load sharing hot swappable power supplies have been available in substation rated networking equipment for several years and should be used whenever possible. These power supplies should be connected to independent

power sources such as AC supply and substation battery to protect from both supply failure and equipment failure.

The new intelligent substation under IEC 61850 frameworks is expected to witness an increased adoption of process bus networks using merging units (MU) and sampled measured value (SMV) data streams. SMVs are digitized real time measurements of the power network that require an accurate time stamp. IEEE 1588 is the recommended technology to provide the precision time stamping required for SMV and Ethernet switches supporting IEEE 1588 are an essential part of the precision timing network. Ethernet switches with transparent clock functionality preserve the accuracy of the time signals as they propagate through the network. Even if process bus and SMV are not deployed today, ensuring the implementation of IEEE 1588 support now will allow an easier migration in the future. Another substation application that requires high precision time signal in the range of microseconds is Wide Area Monitoring based on Synchrophasors or PMU (Phasor Management Units). While utility grade Ethernet switches with IEEE 1588 precision network based time synchronization have been available for more than 5 years, it is not widely supported by protection and control relays. In the past, distribution of precise clock signal required dedicated wiring and could be achieved either with IRIG-B standard or PPS (pulse per second – IEEE 1588 protocol provides the advantage of having a single networking infrastructure both for critical protection, control and measurement data as well as for highly accurate time signal. One of the valuable features of networking equipment is the capability of having legacy IRIG-B and PPS interfaces in order to support smooth migration to IEEE 1588. In such scenario an electrical utility can deploy IEEE 1588 based communications network even if they would still have to use non-IEEE 1588 aware IEDs, as for those IEDs a local “last meter conversion” from IEEE 1588 to IRIG-B or PPS can be done. We can envision a native IEEE 1588 network across the substation switchyard built with IEEE 1588 transparent clocks (Ethernet switches with hardware time-stamping capability) which, if needed, can provide legacy timing outputs justW to the desired IEDs in the bay protection and control cabinets. The only required component in such scenario would be IRIG-B / PPS output card in the IEEE 1588 network switch.

Apart from functional requirements for next generation of substation Ethernet switches need to support IEC 61850 Process Bus, Synchrophasors and other

Example of substation grade Ethernet switch with hot-swappable power supply modules and field-replaceable communications media modules

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Author

Mr. Sumit Deb Senior Manager - Business Development (PD PACI) Siemens Ltd

the adoption of new technologies is just a matter of time before it all becomes a reality in the evolution of an intelligent future substation; optical sensors are already emerging technologies in electrical grids but there will be more and more sensors to monitor all kind of apparatus, be it in the application of circuit breakers, transmission lines, measurement transformers, power transformers, detection of faults etc to name a few. In summary, the substations of future will be all digital, meaning analog information will have to be digitized by intelligent sensors (e.g. merging units) and streamed at high frequency to protection IED, and in the mid-long term future to computer based protection and control servers. This will definitely require lots of processing power and bandwidth in the network.

Migration Strategy towards IEEE 1588 aware substation network

applications of tomorrow along with a robust hardware design. The wide temperature ratings and high immunity to EMI will ensure flawless operation in the unprotected and harsh substation environment. Lastly,