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Abstract—CIM standards for network model exchange have
been around for some time, providing a vendor neutral standard by which utilities can exchange models of their respective networks in either operations or planning contexts. These exchanges take place repeatedly as updates are made to network models to reflect changes in the real systems. Users of network analysis also rely on schematic or pseudo-geographic presentations, which also change as the network models change. Recently, IEC TC57 WG13 has developed a companion standard to CIM model exchange that allows utilities to exchange these schematic layouts as well. The standard makes a distinction between the complete specification of a graphic display and the ‘layout’ of the display that is covered by the standard. This is an important distinction and this paper discusses some of the key use cases for which the new display layout exchange was designed.
I. NOMENCLATURE CIM: The IEC TC57 Common Information Model is a
semantic model governing data exchanges in power systems operation.
II. INTRODUCTION Network models and network analysis results are very
difficult to understand from tabular data alone. The use of schematic and pseudo-geographic diagrams of various different kinds is a long-standing practice that goes back to pre-computer hand-drawn maps and manually constructed wallboard diagrams. Significant amounts of labor go into the definition and maintenance of these schematics. When utilities receive network models, they do not want to invest resources to create diagrams for those models. To date, however, they have not had a way to acquire the diagrams that are used by the source utility for the network model. Their only recourse has been to rely on schematic generation algorithms, which though better than nothing, are not capable of producing a generally satisfactory view without manual assistance and certainly don’t reproduce the views used by the source – and it is sometimes quite useful for the receiver to be able to see the same presentation as is used by the source.
This paper outlines how the new CIM display layout exchange standard (IEC 61970-453) works and then walks through some of the use cases that the designers intended to address with the standard.
Jay P. Britton is with Alstom Grid, Redmond, WA 98103 USA (e-mail:
jay.britton@alstom.com).
III. SUMMARY OF THE STANDARD The first thing to understand about the standard is what it
does and doesn’t do. It does exchange the location and graphic style of each object that is to be displayed – we call this the ‘object layout’. It does not exchange the way that each object is rendered graphically or describe the user interactivity that may be associated with the object. Let’s call this the ‘object realization’.
The layout is a fairly simple structure consisting of ‘triples’ of information for each object placed on the diagram. Each triple contains: a) the identification of the power system model object that is being displayed, b) the location of the object on the diagram (or a set of locations in the case of something like a line), and c) a label indicating the realization style used in the source display.
The realization style label is a sort of proxy for the graphic rendering and interactivity behavior (the object realization) that is not described in the standard. What a source does in encoding a display is to assign a graphic style label to each kind of object realization it uses. For example, if your source display has two ways to show transformers (perhaps a vertical and a horizontal version), then you would use two style labels reflecting this. In order to actually render a display, the receiver then must first set up its display rendering system with object realization specifications for each style used in the exchange.
It is typical of EMS display management systems that they support the ability to define such object realization styles. Typically, what an EMS owner does when they initially receive an EMS is to define a library of the realization styles that their schematic displays will use. After that they define the layout of actual objects linked to the appropriate realization styles. As time passes and the owner performs model maintenance, adding or deleting objects, a parallel chore is to modify the display layouts – but typically there is no need to change the realization styles.
This separation of layout from realization in most implementations makes it possible to define a standard that only deals with layout, but there are two other reasons that we chose to go in this direction. The first is that there are very significant differences in the way that different vendors have implemented object realization, so a complete standard would have been orders of magnitude harder to achieve. The second is that in many of the use cases we examined, the user actually did not want to reproduce the behavior of the source.
Use Cases for the New CIM Standard for Exchange of Schematic Display Layouts
Jay P. Britton, Fellow, IEEE
978-1-4577-1002-5/11/$26.00 ©2011 IEEE
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We are, however, left with the fact that, as the standard is defined, there is a setup step that must be completed prior to being able to use a given type of diagram from a given source. In that step, the receiver defines (in his receiving application) how to realize each graphic style. And of course, this means that for any application that can import the standard, there must be the capability to define object realizations.
The design of the standard implicitly assumes that in most cases, the receiver’s rendition of the exchanged display will have neither the exactly the same look nor exactly the same feel as the source’s rendition. This may be true either because the receiving application is not capable of duplicating what the source does or because the receiver does not want the same behavior. Nevertheless, receivers can derive considerable value from the ability to receive and duplicate the layout, as is illustrated in use cases given in the following section.
IV. USE CASES FOR DISPLAY LAYOUT EXCHANGE In this section we elaborate on some of the expected use
cases for the new exchange standard.
A. Member company schematics to regional ISO/RTO. Probably the most basic use of display layout exchange in
transmission operations is the exchange of a schematic along with the power system models. Figure 1 shows a typical pattern of exchange between an upper level interconnection wide organization and its member transmission owners (TOs).
CompleteInterconnection
Model
My External Models
TO 1
TO 2
TO n
My Internal Model
My External Models
My Internal Model
My External Models
My Internal Model
Figure 1. Interconnection model exchange process .
The pattern here is straightforward. Each TO is responsible
for modeling its own territory and for making that model available to the interconnection operations entities using the CIM model exchange standard (IEC 61970-452), shown as the blue paths in the figure. If the TOs have agreed on boundaries using the CIM standard, these submitted models may be merged without modification of any sort to form a complete detail of the interconnection. EMS or planning systems operating at the interconnection level might use this model
directly, but the interconnection model may also serve as the source for TOs to maintain up-to-date external models representing their neighboring utilities. They do this by importing what they need, again using the CIM model exchange standard (shown as the orange paths on the diagram).
CompleteInterconnection
Model
My Neighbor’s Schematics
TO 1
TO 2
TO n
My Schematics
Interconnection Schematics
My Schematics
My Schematics
My Neighbor’s Schematics
My Neighbor’s Schematics
Figure 2. Interconnection display exchange process
Figure 2 shows that the identical pattern may be used to add display layouts to this model exchange process. The layouts are transmitted in separate files but they are defined with CIM Master Resource Identifier (MRID) references to the model objects. They are therefore usable both as schematic layouts for the complete interconnection model or for any of the external models derived by TOs, provided of course that the CIM convention of maintaining the MRIDs is followed everywhere.
Any type of schematic may be encoded as a CIM display layout. Substation one-lines would probably be the most common, but wallboard diagrams and other wide area views can also be captured. Recommended practice would be for each source to encode the diagrams that they use, selecting realization styles that match the way their diagrams are defined. These realization styles should be communicated to the rest of the participants, but at this time, there is no standard for expressing this because the step to define interpretation of the realization styles is manual. The burden is on the receiver to create realizations.
Suppose that each TO sends their SCADA substation one-lines. In their systems, the realization logic in these diagrams is quite complex, allowing for controls, for alarms, for tags, etc. A receiver is probably just interested in showing the state of the system in the same layout, so the receiver can and should create much simpler realizations, sometimes ignoring some graphic placements altogether.
To take a few examples, a receiver would want to duplicate the basic object shapes of course – lines, transformers, breakers, generators, etc. Names would be the names in the system that was rendering the display, which means that in some cases they might be different from the source. The
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receiver would want calculated flows and voltages, but probably not measurement fields unless they were receiving ICCP exchanges from their neighbor. Fields for alarms or tags would not be shown. Controls would not be implemented. The exact translation can be very situation specific, and the generic nature of the standard allows for this variation.
B. Preserve schematic investment in EMS replacement. Another obvious use case is an Energy Management
System (EMS) replacement. This does not happen often, but when it does, the utility will often want to have a competitive bid in which there is the possibility that a different vendor would be awarded the contract for the new system. Obviously, the utility will not want to have to repeat the expensive and difficult process of defining power system models and building schematic presentations from scratch. This would be undesirable from a pure cost standpoint and because it unbalances the competitive bid playing field if the current vendor has a cost advantage over the others.
So, the objective of this use case is to export models and displays from the existing system to the new system, regardless of whether the systems are from different vendors. To refine this a bit further, however, a standard does not have to be able to transfer everything in order to be valuable. There is value to the exact extent that investment in the models and displays are preserved.
As in the previous use case, this situation would begin by exporting the source displays, as they were defined, with references to a companion CIM model export.
The next step would be to examine the compatibility between the object realizations that would be desirable for the new system and the object realizations used in the old system. Differences among EMS vendors could mean that there is not a one-for-one mapping and some processing of the export is required. Consider the situation illustrated below.
Figure 3. Simple transformer picture.
In some vendors systems, this may be one object placement (the transformer) that includes the watt/var values. In other vendor systems, this may be defined with separate object placements for the transformer and the two values. If the source is a single placement and the new system has to represent it as three, or vice versa, some sort of custom transformation needs to be constructed in order to get the desired result.
This transformation is more important to accomplish here than in the previous use case (where the same situation can occur), because these are the mainstream user displays and they need to work the way the new system is designed to
work. Generally speaking, however, these transformations will be far less costly (and less error prone) than any other acceptable option for initializing the new system.
Once an effective transformation is developed for the realization styles of the new system, a CIM import can be used to initialize that system. The end result in most cases will be effective, but not perfect, preservation of investment.
C. Distribution feeder diagrams GIS to DMS. For distribution operations, it is common that utilities
maintain feeder data in a GIS environment that has been adapted to define feeder electrical connectivity as well as the geographic location of distribution assets. In this case, what resides in the GIS should probably be considered a pseudo-geographic schematic, because it will allow a user to distinguish what is connected to what at the same location.
Usually if a real-time Distribution Management System (DMS) is added, it will be a requirement that the DMS acquires its feeder diagrams from the GIS, because it would be an unacceptable amount of work to maintain this information in two places – and the GIS normally is already in place as the master source. Such interfaces have already been built by extending the CIM model exchange standard, but the new standard offers more complete coverage.
Usually in this context, it is not important that the DMS displays look and feel closely resemble the GIS look and feel. The main thing that is required is to use the location and connection information for the physical feeder objects so that the DMS can produce displays on a physical map background. These GIS-DMS interfaces are very intensely exercised, as distribution construction is a daily activity. Support of the standard by GIS and DMS vendors probably has more of a ‘get close’ compatibility goal, rather than an ‘out-of-the-box’ compatibility. In most instances, when two GIS and DMS systems are married, it will be worthwhile to customize the GIS generation of layouts – in particular the use of realization styles – to line up with the DMS requirements, although it is also possible that standardized choices of styles could evolve as CIM is applied in this domain.
One nuance here that may be important is a requirement to transfer both the real geographic position and pseudo-graphic schematic positions that are necessary to present connectivity clearly. There is only one real geographic position, so in CIM, the geographic positions are considered part of the power system model and should be transferred with that information. Pseudo-graphic schematics, on the other hand, would be handled by the layout exchange we are discussing here, allowing both to coexist.
D. Auto-generation tool for display layout. Our final use case involves the improving the utility of
auto-generation algorithms. Effective auto-generation of network diagrams from an underlying network model has been a holy grail of sorts in the electric utility industry. Many attempts have been made and continue to be made. The present state of the art is that some algorithms exist that are useful for certain kinds of diagrams in certain usage contexts,
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especially if they are integrated with the ability to manually adjust the results (and remember the adjustments as models evolve), but no universally satisfactory answer exists.
An obstacle that holds this whole endeavor back is that most algorithms currently are embedded within some proprietary power system model and display description system and they don’t mix and match. In other words, there may be an array of algorithms out there, but you cannot just try them out on your particular display problem to see which one produces a good result, because the data structures in and out are not compatible.
If, however, power system models are managed in CIM terms, and if the display layout algorithms support the CIM layout standard, then the world of auto-generation becomes interoperable. Because there is no one single approach that is always best, achieving such CIM compatibility offers the utility industry a much greater chance of reducing the amount of manual effort involved in creating and maintaining schematic displays.
V. CONCLUSION The development of the display layout exchange standard
is an important advance in the CIM family of standards. The choice to separate layout from realization delivers clear benefits while maintaining a simple and cost effective design. The general nature of the graphics exchange standard makes it possible to address many different situations that require schematic exchange.
The main question surrounding the standard is whether, as we begin to see more real implementations, it becomes apparent that we also need a standard for exchanging object realization – that is, for exchanging the graphic rendering and interactivity logic implied by the graphic style labels.
VI. REFERENCES
Standards: [1] CIM Static Transmission Network Model Profiles, IEC TC57 61970-
452, Oct 2010. [2] CIM Based Graphics Exchange, IEC TC57 61970-453, May 2010.
VII. BIOGRAPHY Jay P. Britton (M’1968, F’1997) was born in DeKalb, IL, USA in 1945. Mr. Britton is a graduate of Princeton University. He was a founder of ESCA Corporation in 1979. He is currently a Senior Product Manager with Alstom Grid Corporation. He was made Fellow of the IEEE in 1997, “for contributions to software architectures and to applications
in electric utility energy management systems.” He is currently an active participant in developing CIM standards for EMS and Smart Grid systems as a member of IEC TC57 Working Groups 13 and 19 and the Smart Grid Architecture Committee in NIST’s SGIP.
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