by Fred Steinhauser, OMICRON electronics GmbH, Austria
Protection engineers do not embrace the concept of shared buses.
Back in 2001,when IEC TC57 WG12 (which was later merged, together with WG11, into WG10) was standardizing IEC 61850 Sampled Values, there were still many people which felt extremely uncomfortable with the concept of a process bus. One outcome of this was IEC 61850-9-1, named “Sampled values over serial unidirectional multidrop point to point link” [sic!]. What a title, you need a committee to come up with something like this.
The technical essence or nonsense of this title can be seen in two ways: There is no Ethernet variant specifically foreseen for point-to-point links at all. On the other hand, each link between an end device and a modern Ethernet switch is point-to-point, as no shared media are used any more. Or in other words, nothing would have ever kept a “9-1 merging unit” from being connected to a bus and working fine.
IEC 61850-9-1 is now long gone, but the mistrust against communication buses seems to live on in the PAC community.
It is not explicitly admitted, but reading between the lines, there are many symptoms that always reflect this tendency towards point-to-point thinking. So, why do protection people obviously feel so uncomfortable with the bus concept? It might be the fear to lose control, that there is some chaos going on in the bus. By the time, I have heard all kinds of strange assumptions about the weaknesses and imponderables of the communication networks. I remember a statement made at a conference in 2005: a protection engineer said that the 3 ms delay of GOOSE messages in the network was unbearable. From the fact that there was a 3 ms figure in IEC 61850-5 as a maximum value for a certain performance class, he deducted that GOOSE messages will always be delayed by this amount.
When it comes to political correctness, we have accepted that language reveals the attitude of the speaker. Likewise, the wording used for some concepts discussed in Power Utility Communication discloses the thinking behind it.
The “process bus per bay” is such a term, sometimes heard, but hopefully not really implemented. Where is the bus in this case? This is a contradiction in itself. How is then information shared between bays, when each one has it own bus?
Also, we hear of “GOOSE Servers” that “send a GOOSE to device XYZ”. This wording neglects the correct publisher and subscriber terminology and the concept connected to it. Of course, no sensible designer will configure a GOOSE message to be published without having a subscriber in mind. But the publisher just sends the GOOSE on the bus, not even knowing which devices will subscribe to it. The “connection-oriented” wording is another symptom of the point-to-point mindset.
We have seen drawings labelled with VLAN numbers as if they were wiring designations. “One MAC address for each GOOSE” or “one VLAN for each …,” are simplistic rules, suggesting extreme granularity for traffic management and tight control of where each piece of information will go. This is easily said, but hard to manage. And it is far from optimal.
Grouping traffic by MAC address or VLAN could be much more efficient, but it requires thorough planning and thinking.
Power Utility Communication done right requires shifting the focus. The PAC people need to team up with the communication guys. Start the thinking with the data flow, design the communication network and build the rest on top of it.
Yes, this is a paradigm shift. But to make most out of it, this is the way to go.
Fred Steinhauser studied Electrical Engineering at the Vienna University of Technology, where he obtained his diploma in 1986 and received a Dr. of Technical Sciences in 1991. He joined OMICRON and worked on several aspects of testing power system protection. Since 2000 he worked as a product manager with a focus on power utility communication. Since 2014 he is active within the Power Utility Communication business of OMICRON, focusing on Digital Substations and serving as an IEC 61850 expert. Fred is a member of WG10 in the TC57 of the IEC and contributes to IEC 61850. He is one of the main authors of the UCA Implementation Guideline for Sampled Values (9-2LE). Within TC95, he contributes to IEC 61850 related topics. As a member of CIGRÉ he is active within the scope of SC D2 and SC B5. He also contributed to the synchrophasor standard IEEE C37.118.