Network Model Alignment Part 1: Understanding the “What”

In the first installment of this blog series, we will be reviewing how network models are used in electric utilities and make a case for organizing key planning and operations activities around having a singular, rather than multiple, model representation of the network.

Grid Operations need network models that can represent networks in their present state or for a few hours into the future. For that reason, operational EMS network data is based on a node/breaker model which explicitly models physical equipment and devices.

Advanced numerical network analysis applications in the operations environment, such as state estimation, power flow, optimal power flow, short circuit analysis, etc., however, use an abstract model of the network, typically, referred to as a bus/branch network model. These models eliminate the switches and circuit breakers based on their open/close status.

Near-term planning dealing with next day/week with short-term load forecasts based on weather forecasts, etc. need to be able to assess network capacity and generation demand to achieve grid reliability goals. This type of planning software uses bus/branch models that are derived from the node/breaker model through a process usually called topology processing (TP).

Topology Processing needs to retain the mapping of the physical assets to the abstract bus/branch model in detail. In this representation of the network, busbar sections with closed switches are modeled as a single bus (node). If they are not, snapshots of network status will lose reference(s) to the physical busbar sections and switches.

Long-term planning deals with next month/season/year with annual load growth to determine schedules for incremental network expansion, such as adding micro-grids, renewable generation farms, etc.

• New network designs associated with network expansion, switches and breakers are not added at this stage of design, resulting in bus/branch network models.

So, why have a single unified network model for both planning and operations?

Eliminates the need to maintain multiple network models independently. In the past, planning models (bus/branch) were maintained in the planning environment. Quite often there was the need to use multiple planning applications, each with its own proprietary model. Exchange between these various planning apps required custom translators for each pair of planning apps involved. EPRI recognized the need to have a single common language that each planning app could map to once and be able to communicate with all other planning apps that also had mapped to that common language. EPRI funded a project to extend the CIM UML model for this purpose. Since CIM UML was already a standard for exchange of operations (node/breaker) models, this extension also embraced the conversion of planning models to operations models for use in an EMS without having to re-enter all the model data manually, saving hours of labor and reducing the introduction of errors in the process. So, planning models could now be imported into the operations environment, where the necessary switches and circuit breakers could be added. Conversely, planning could also import operations models into the planning environment in order to have an as-built model to do case studies against.

Creates opportunity to have a single Network Model Manager. With the exchange of all network models based on the CIM, it then became possible to have a single Network Model Manager that would allow a single point of entry for updates to the network model, followed by exports to both operations and planning.

Final Thoughts

Aligning planning and operations models may seem to be a daunting and overwhelming task in a utility where the quantity of busses engineering needs to elaborate numbers in the thousands. Xtensible recommends as a preliminary step to embarking on the alignment journey that utilities conduct an assessment to ‘measure the size of the problem’, assess its current capabilities, align people, processes and technology and identify any opportunities for streamlining the process via data profiling and automation which could potentially save hundreds of hours of effort.

In part two of this blog series, we will provide details on how the CIM supports alignment to and management of a single network model to support both planning and operations as well as some real-world applications of it.

In the meantime, check our recent blog post of Are Utilities in the U.S. Utilizing the IEC CIM, this can give you some insights into who is taking this approach.