Learning Objectives
- Understand the history of the CIM
- Understand some of the basic components of US and European style markets
- Understand the IEC standards process and phases
Origins of the Utility CIM
Exchanging power systems data between utility companies has been problematic when proprietary formats are used. In the past a company would traditionally use a single software system, whether a custom in-house solution or whether purchased from a large software company, and there would be a single proprietary data standard and format used. With the deregulation of the power industry, the emergence of smarter grids, and the integration of consumer or third-party distributed energy resources (DERs), there is now a greater need to enable interoperability across a wide diversity of companies and systems.
The increase in choice provided by the number of power system software vendors and the different software packages and architectures available add to the challenge of data exchange. These issues point to a requirement for a single, open standard for describing electric utility data and to aid the interoperability between software packages and exchange of information both within one company and between companies.
The Common Information Model (CIM) was developed as an open standard for representing power system components. CIM was originally developed by the Electric Power Research Institute (EPRI) in North America and is now a series of standards under the auspices of the International Electrotechnical Commission (IEC). The standard was started as part of the Control Center Application Programming Interface (CCAPI) project at EPRI with the aim of defining a common definition for the components in power systems for use the Energy Management System (EMS) Application Programming Interface (API), now maintained by IEC Technical Committee 57 Working Group 13 as IEC 61970-301. The format has been adopted by the major EMS vendors to allow the exchange of data between their applications, independent of their internal software architecture or operating platform.
Technical Committee 57 Oversees Power Systems Modeling
IEC Technical Committee 57 was established in 1965 to develop standards for “Power systems management and associated information exchange”. The CIM standards are developed and maintained by three working groups under IEC TC57, working groups 13, 14, and 16. A further group, Working Group 19, is responsible for coordinating interoperability within TC 57 in the long term and harmonizes work across the TC57 working groups. This helps ensure there is no duplication of effort and promotes consistency and interoperability between the standards.
Working Group 13 Focuses on Power System Models
Working Group 13 maintains the core CIM model as language-independent UML model, defining the components of a power system as classes along with the relationships between these classes: inheritance, association and aggregation; and the parameters within each class are also defined. This provides the foundation for a generic model to represent all aspects of a power system, independent of any particular proprietary data standard or format. This simplifies the interoperability between software applications, since there need only exist a translator to convert to and from the CIM based data, where previously there would have been the need for translators to convert to and from every other third party company’s proprietary format.
The CIM as defined in WG13 covers the modeling of electrical networks from the perspective of the transmission system operator and so is focused on the definition of the electrical network and applications linked to online operations and offline analysis of the network.
Working Group 14 Focuses on Distribution Management and Enterprise Integration
Extensions to the CIM were subsequently added with the scope being that of system interfaces for distribution management systems. These extensions are maintained and developed by another working group under Technical Committee 57, Working Group 14. These extensions expanded the CIM beyond its roots in the transmission EMS world into the distribution network and the modeling of data exchanges between systems within the distribution utilities and distribution system operators (DSOs).
The original electrical model was expanded to include the modeling of unbalanced, low, and medium voltage distribution networks as well as DERs. Extensions addressed the needs of Network Operations, Records and Asset Management, Operational Planning and Optimization, Maintenance and Construction, Network Extension Planning, Customer Support, and Meter Reading and Control. This significantly increased the scope of the CIM; although these extensions were originated for distribution utilities, there is a growing recognition that many are also applicable in the transmission domain.
This part of the CIM is then used to derive interfaces primarily for systems integration within the utility. How these messages are derived will be discussed later.
Working Group 16 Focuses on Deregulated Energy Market Communications
The CIM for Markets Extensions (CME) was created to expand the use of the CIM into the area of deregulated energy markets. These extensions cover the data required for electricity market operations including bidding, clearing and settlement. These extensions model the data that is communicated between market participants, not a model of the structure of the market itself. There are two primary sub teams within the working group, one creating extensions for European-style markets, the other for US-style markets. These two styles have different characteristics:
European Style Markets:
- Ahead Markets: Bilateral
- Intra-Day Markets
- Balancing markets
- Collaboration with ENTSO-E
US Style Markets:
- Day Ahead Markets with Security Constraint Unit Commitment (SCUC)
- Hour Ahead Markets
- Real Time Markets with Security Constraint Economic Dispatch (SCED)
- Collaboration with ISO/RTD Council and ISO projects
Electricity markets often vary between implementations and so CME is seen as a starting point on which extensions can be added to support a particular market implementation.
Working Groups are Evolving with Grid Modernization Efforts
In recent years WG 13 and WG 14 participants have recognized that the respective roles of the working groups have been evolving in concert with the changes underway with grid modernization. These working groups were originally structured to follow the common utility separation of transmission and distribution organizations, business processes, and computing systems. Today, while there are still differences, that distinction is proving to be more of a hindrance than a benefit.
For example, rapid DER adoption in some markets drives the increased need for network model data sharing in the distribution domain and across the boundary with transmission. Likewise, DER aggregators will participate in markets, competing with independent power producers and vertically integrated utilities to provide grid services to transmission operators. This will shift traditional distinctions between generation, transmission, and distribution domains. DER providers will grow in complexity, in some cases managing energy storage systems, EV recharging stations, home energy systems and many other types of resources – all of which will require some level of modeling.
Around 2016, a decision was made that WG 13 would assume responsibility for distribution network model data. In the same time range, the value of the WG14 CIM asset model to data exchange in the transmission domain was recognized. The working groups now divide modeling responsibility primarily by the type of data as opposed to the voltage level. In addition, WG 16 is currently sponsoring a DER modeling task force where working groups 10, 13, 14, and 16 are represented.
These changes are designed to align with a new Interface Reference Model that is currently under development and to more clearly identify work gaps and responsibilities. The evolution of these working groups will continue into the future years, guided by Working Group 19.
Standards Process
The International Electrotechnical Committee is based in Switzerland and, as a global standards authority, requires the CIM and all related standards to go through a formal standards process before publication. This process contains a number of steps:
Step 1: New Work Item Proposal
A new work item proposal is the first step in creating a new standard. The NWIP is submitted by a working group and is voted on by all member countries. A minimum of 5 countries must provide experts to work on the proposal and a majority must vote in favor for it to move forward in the standards process.
Step 2: Working Draft and Committee Draft
The working group then prepares a working draft of the standard, which may take months or even years to prepare. This is then submitted as a Committee Draft (CD) that is circulated to all national committee for comment. These comments are then compiled and sent to the working group to be addressed.
Step 3: Committee Draft for Vote
After addressing the comments received from national committees about the CD the working group then prepares an updated version of the standard that is issued as a Committee Draft for Vote (CDV). This is circulated to member countries for a five-month voting period and is considered approved if two thirds of the votes cast are in favor and the number of negative votes does not exceed 25% of the votes cast. At this stage countries may still submit comments along with their vote.
Step 4: Final Draft International Standard
The working group, once again, addresses any comments that have been received and prepares a Final Draft International Standard (FDIS). This is submitted to the IEC Central Office and circulated to the national committees for a two-month voting period. At this stage a country may only make an explicit vote: positive, negative or abstention.
The FDIS is approved if two thirds of the votes cast are in favor and the number of negative votes cast does not exceed 25% of the votes cast. If approved, the document is published however if the conditions are not met it is referred back to the working group to be revised. Final publication is the responsibility of the IEC Central Office and leads to the publication of an international standard. This normally takes place within two months of the approval of the FDIS.
Standards Cycles Can Take Years of Time
The standards process can take a significant period of time:
- Committee Draft for vote: 5 months
- Final Draft International Standard vote: 2 months
- Addressing comments: up to 4 months
- Publication: up to 2 months
In addition, there is the time to prepare the NWIP, WD and CD with additional time in between all of these stages for experts to work on the drafts. As such the process can take several years from inception to the publication of the standard.
With such a long cycle time, some users choose to work with draft documents before final approval issued.; however, there is a risk that drafts may change before final publication. Any projects using draft documents should take this into account and plan accordingly.
Case Study
Jeff Kimble has mentioned to some of his colleagues that he is interested in CIM and learning how Electric Innovation Utility could leverage the model for their operations and integration. Unfortunately, the responses from his colleagues have run the gamut from a lack of awareness, to several negative impressions, such as:
- “It takes too long for the CIM to be updated.”
- “Nobody uses that.”
- “Don’t we have our own common model?”
- “The standard is always changing, how could we possibly deal with that?”
What would explain some of these perceptions and questions that Jeff’ colleagues have?
It does take a long time to update any given standards document within the IEC. The process is, by design, structured to give all participating countries an opportunity to comment on the content. While this makes the process take longer, the resulting standards have broader, international support, and are typically more robust.
A response that reflects that the speaker may not be aware of what standard the applications they use behind the scenes for its data model or integration.
Often, especially for larger utilities, they may have their own data dictionary. But often the common “vocabulary” is not used across the organization but may only be in a few silos, that is, data administration, or perhaps the engineering analysis teams. The use of the CIM not only facilitates cross-domain communication and semantic understanding, it also supports broader communication with other vendors and utilities.
It is interesting how often in the user group community desperate messages are heard; these may include “it takes too long” or “it changes too frequently”.
CIM-based integration can support the change management capabilities of any vendor’s interface, using service level and XSD versioning, as well as supporting backwards compatibility.
The Standards Development Organization responsible for CIM maintenance is:
A
Organization for the Advancement of Structured Information Standards (OASIS)
B
International Electrotechnical Committee (IEC)
C
National Institute of Standards and Technology (NIST)
D
North American Electric Standards Board (NAESB)
B. International Electrotechnical Committee (IEC)
IEC 61970, maintained by TC57 WG13 is often referred to as the 'core' because:
A
Due to the acronym 'Center for Object Related Extensions'
B
Because the standard was approved with two-thirds vote
C
Because it is for deregulated energy markets
D
Because it defines the components of the power system
D. Because it defines the components of the power system
The time to go from New Work Item Proposal (NWIP) stage to a Final Draft International Standard (FDIS) is typically:
A
More than a year
B
Six months
C
Five months
D
Up to two months
A. More than a year
The IEC 61968 extension to the original CIM added:
A
Transmission network descriptions
B
Energy market descriptions
C
Unbalanced, low and medium distribution networks
D
Unified Modeling Language
C. Unbalanced, low and medium distribution networks
How many countries must vote to approve a New Work Item Proposal (NWIP):
A
5
B
10
C
4
D
One from North America and one from Europe
A. 5