CIM and ODM

During the ODM presentation in IEEE PES GM2009 in Calgary, a question about CIM and ODM was raised. The question was "IEC CIM (Common Information Model) is a information model designed to model power network. CIM has been accepted by the power community world-wide. Why we need ODM, which is yet another power system information model?".

Before answering the question, let us discuss what is CIM, as well as ODM:

• CIM is a data object model, designed to model/describe physical power networks. Information, such as connectivity of physical equipments, equipment physical size, equipment geographical location (attitude and longitude) as well as equipment electrical parameters (R, X, Rating), are included in the model. A substation CIM view is shown in the above figure. If a power network were broken apart, with its CIM model, theoretically, we could re-assemble the parts together to re-construct the original power network.
  • ODM is designed to represent a power network in a logic way for power system simulation. The ODM view, shown in the above figure, is a one-line diagram view of the same substation. Almost all modern power system simulation algorithms are built on the node admittance Y-matrix. One of the ODM design goals is to minimize possible ambiguity to implement Y-matrix based solutions. Network, Bus and Branch are three most fundamental concepts in ODM.

As we all know, there is no "One Shoe Size fits All" in real life. CIM and ODM are designed for different purposes. There is no doubt that a full CIM model could contain all information necessary for power system analysis. The information could be extracted and used directly by a power system analysis program. However, a full CIM model is usually very large. For example, the current ERCOT CIM model, when represented using a RDF/Xml file, is 4.5G in size and has about 2.6M RDF records. It is very challenging to process the model file itself using currently available tools, commcercial or non-commercial.

As a part of the ODM initiative, an adapter will be developed in the near future to extract only information relavent to power system analysis from a CIM model and transform the information into an ODM Xml file, as shown in the figure below. The implementation will be based on the CIM CPSM (Common Power System Model) Profile, which currently is still under development.

The relative small size of the ODM circle, compared with the CIM circle, indicates that the ODM model contains a subset of the original CIM model info, which should be much easy to deal with.