DNP vs. IEC: Skirmish in the Substation

By Kathleen Davis, senior editor

Communications for the utility set parallels the amorphous smart grid in one significant manner: It’s a lot of tech, hardware, software and details all under a big, generic umbrella term. The difference between the two lies in what’s underneath. The industry has yet to figure out the foundation of its favorite smart grid terminology, but it knows what supports its communications: protocols.

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A war over the proper love for the proper protocol is going on for the hearts and minds of North American substation engineers. Will they choose the old favorite DNP3, or will they select the popular IEC 61850?

To look at both sides, Utility Automation & Engineering T&D called upon a veteran of this fight, Bruce Muschlitz.

A consulting engineer with EnerNex specializing in utility data communications, Muschlitz chairs the UCA International Users Group conformance testing committee for IEC 61850-based products. He is also a member of IEEE-Communications Society, Computer Society, Power Engineering Society and Standards Association and the DNP3 Technical Committee, and he’s a U.S. delegate of IEC TC 57 working group 10.

Muschlitz knows both sides.

Why Can’t We All Just Get Along?

A battle is going on between proponents of DNP3 and proponents of IEC 61850. Muschlitz, however, isn’t a fan of declaring them enemies.

“I knew this question would arise,” he said when asked which protocol would win, “but I am a member of both the DNP3 and IEC 61850 technical committees and firmly believe in the cross-pollination of technologies between the two groups.”

Considering the history of both protocols, Muschlitz said that the two have been converging “in terms of capabilities,” even if they started on opposite sides.

DNP3 is designed to focus on inexpensive endpoints and low-bandwidth communication channels while IEC 61850 is designed for high-bandwidth communication channels with a richer, wider range of features, Muschlitz said. Both protocols must adapt to increasingly loud calls for flexibility.

“This will drive the industry toward an IEC 61850 solution, but I expect DNP3 to be the dominant North American protocol for at least another three years with a gradual decline after that,” Muschlitz said.

IEC 61850 is already the dominant protocol in Europe and India. Muschlitz thinks it probably will win over North America, as well.

Why’s it taking so long?

Many European utilies quickly accepted IEC 61850, but in North America it slowly garners a convert here and there.

Muschlitz blames this divide on cultural differences. North Americans are interested in the overall view, making DNP3 a better choice right now.

“North American utilities differ from others around the world in that we like to purchase best-in-class devices while the remainder of the world prefers to use single-vendor solutions,” he said. “This has a lot to do with American preference for highly optimized systems, whereas others prefer simplicity in system integration.”

Bucking popular opinion on IEC 61850, Muschlitz still sees problems with the multivendor system adopted with IEC 61850. He opts for the simplicity and ease of a single-vendor choice. Older protocols such as DNP3 have had time to evolve and to become familiar. IEC 61850 requires a reboot that will unearth “growing pains,” as Muschlitz described them. As IEC 61850 mellows from radical to typical, those problems should decrease. That’s why North American utilities are waiting to adopt IEC 61850–for things to smooth out, Muschlitz said.

Advantages and Disadvantages

Like all protocols, IEC 61850–the predicted winner of this protocol battle–has positive points.

“IEC 61850 isn’t just another protocol; it is a new way of solving a system problem,” Muschlitz said.

He noted that IEC 61850:

  • begins with specification requirements,
  • moves to detailed specification,
  • provides an electronic documentation methodology, and
  • allows evolution of the system in a controlled fashion.

While the products of IEC 61850 might come together piecemeal and willy-nilly, the major advantage of the protocol is a wider view of those four points. In the past, each was considered separately. Different issues had different solutions: specification issues required one solution, details within those specifications needed a different solution, documentation focused on a third solution, and evolution was someone else’s problem. IEC 61850 changed that.

“IEC 61850 has shown that a unified approach to system engineering can reduce overall costs,” Muschlitz said. “IEC 61850 also supports the GOOSE concept, which allows vast reductions in interdevice wiring and the realization of the copper-free substation. In fact, GOOSE is often touted as the major outcome of the IEC 61850 standard.”

Positives are balanced with negatives, even with this emerging protocol. IEC 61850 is young, untested and hasn’t had time to mellow and evolve.

In addition, IEC 61850’s major advantage–that holistic concept to solutions–is also a major disadvantage for training. It’s different from the old system, requiring “a rather steep learning curve,” Muschlitz said.

“Many people get depressed when the stack of 1,500 pages of IEC 61850 is put in front of them with the directive “Ëœlearn this,’ “ he said.

IEC 61850 also has high-end needs: It requires serious bandwidth. Many Ethernet channels are needed for all the positive features (such as the copper wiring elimination), which tend to cause a fight among the varied protection and telecom engineers involved as they tussle for enough bandwidth to fulfill their own job requirements.

Being new in the field of protocols, the first edition of IEC 61850 had issues that vendors solved differently, leading to a few interoperability issues. The second edition–currently on the drawing board–should solve that and lead to a zip up the interoperability learning curve within the next three to five years.

Muschlitz sees the problems of IEC 61850 common in most new technologies. Its advantages will push the protocol to the top.

“IEC 61850 will eventually win because it has all of the features required by all the stakeholders. Although each group will see these features as advantages for them, the overall system synergies will be the primary driver of IEC 61850,” he said.

Advice and Notations

Muschlitz can predict the protocol because he’s involved with both IEC 61850 and DNP3 committees. Communications is an umbrella term without definition. Even though the battle about protocols rages, committees for both camps still talk definitions rather than surrender.

“I see the same issues appearing in both the IEC and DNP groups,” Muschlitz said. “Each person in the meeting can have very different interpretations of the words in the standard. Often we seem to discuss the intent of the standards’ writers compared to the words written in the standards. We also often find inconsistencies between various parts of the standards. Most of our discussion centers upon “ËœExactly how should we test this specific feature in a vendor-agnostic fashion?’ “

Given that most standards–by the process of how they are written–leave room for interpretation and many options to accomplish one goal, a discussion of definitions might be more relevant than a discussion of victories and defeat. DNP3 still reigns, even if its decline is near. IEC 61850 has a few project inroads as well, even if it hasn’t won just yet. Predictions aside, engineers in the field still must work with the details of both systems.

“If each vendor implements a different subset, then these devices will not be interoperable, even though each passes a conformance test. The assumption by the standards’ writers is that market forces will drive the vendors toward common solutions, but this process is not instantaneous,” Muschlitz said.

While the industry talks overall picture, engineers talk details. The umbrella terms must be dissected, defined and acted upon. That may take the right protocol, but it also takes the right interpretation. Whatever protocol wins, soldiers like Muschlitz will drive the victory.

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