- Sep 23, 2021 9:32 pm GMT
Let’s give a big round of applause for Ajay Bhatt of Intel. He invented the USB - the Universal Serial Bus. His invention simplified connectivity and data interoperability–connecting computers to keyboards, printers, and external hard drives. It’s just too bad Ajay didn’t make it reversible. I don’t know about you, but it takes me three tries to successfully insert a USB plug. The first time it doesn’t fit, I turn it around, it still doesn’t work. But the third time is a charmer. It fits. Other than that, it was a great step forward in connectivity.
CIM is like the USB. It standardizes data interoperability among power system applications. One brand’s SCADA to another, GIS to SCADA, ADMS to SCADA. SCADA to power flow apps. You name it.
Here is a little refresher about CIM. CIM is a graphical representation of all the data you ever wanted to know about an electric utility system. It uses a tool called Unified Modeling Language or UML. To use, the UML must be converted to something useful for data transfer. It uses a popular markup language Extensible Markup Language (XML) that people and computers can read easily.
CIM has a standard way of describing data independent of any product or system.
This blog discusses how it models objects and electric network connectivity. Perhaps one of the more confusing aspects of CIM is the standards numbering system. So, I’ll end with that.
Electrical Network Connectivity – Buses and Lines
Years ago, I taught a course in computer methods in power system analysis. It detailed how to calculate the flow of power over an interconnected electrical network. To do the math, you had to model precisely how the components of the network are connected. There were two crucial elements, buses, and lines. A bus is a single electrical point. A line connects between two buses. The data for analysis consists of information about the lines, the electrical characteristics, and the name of the from bus and the to bus. The set of lines with from bus and to bus creates electrical connectivity. In addition, there is data about the buses, such as power generated at the location or customer demand consumed. The simulation then uses that data to calculate power flows across the network.
It turns out that busses are not single electric points, but devices, like busbars. They have length just like electrical cables, just shorter. So, the CIM founders and others created an artificial object, a connectivity node, which is the place where real electric devices come together. So, each device in CIM that is part of the connected network has at least one connectivity node.
Every power system analysis requires this connectivity data – short circuit calculations, insulation coordination, state estimation, and stability. Get connections wrong, and the analysis is worthless.
CIM – A Class Act
CIM includes all the data about devices, their every conceivable trait, and the connectivity.
CIM is organized around classes. A class is generally a thing, like a switch, a wire, or a lightning arrester. Classes also can be connectivity nodes or measurements. Classes in CIM have traits like size, color, and material. These traits are called attributes. The classes and attributes have exact names. That’s what makes CIM so valuable. Every SCADA, GIS, or ADMS creates different names and representations for objects. That’s what makes interoperability between them so tough. CIM is the intermediate language that makes this process foolproof.
The IEC (International Electrotechnical Commission) Standards
As I noted in my first blog, the original creators of CIM petitioned the international standards group IEC to publish CIM standards. IEC agreed. When this first happened, CIM was limited to the exchange of data between various Energy Management Systems (EMS). Then, IEC formed a working group to refine the CIM UML and publish official IEC standards. IEC assigned this first family of standards, the number 61970.
If CIM worked for transmission, why not for distribution? So, IEC formed a working group for distribution. IEC assigned a different number, 61968, for the family of standards for distribution. This working group created a brand new set of CIM UML. Later still, as electric markets developed, a third working evolved. IEC assigned yet a different number, 62325, for this family of standards. Like the second working group, this one created another set of new CIM UML. None of these three pieces of CIM overlap. However, the single CIMUML consists of these three pieces together. So even though there is a single CIM UML, it consists of three unique pieces.
I get this a lot. “So, what version of CIM are you using?” Since there are three unique pieces of CIM, each has a different version. So, what’s the real answer to the question of the official version of CIM? The isn’t one. There are three versions, one for each of the three pieces of the CIM. What? People like to have a single version for software-related technology. It is the latest version of the UML piece adopted by the first working group. Right now, that version stands at 17. The working groups are now considering using a single name for the official CIM releases comprised of all three parts of the CIM. A long-promised CIM100 might be the result.
Does it Matter?
Not really. Recall from my part 2 blog that no one uses the UML for their interchange of data. Instead, users select a subset, called a profile, of the latest UML CIM based on what they need to do. So, for example, if users wish to create interoperability between GIS and ADMS, they will make a subset of the single CIM UML. They will then convert the profile UML into XML.
That will be the data equivalent of Mr. Bhatt’s USB plug. Hopefully, it won’t take you three tries to make it work.
For more information about CIM, check out the CIM User Group website at www.cimug.org.
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