Different Modelling Philosophies
When discussing power system modeling, engineers often encounter two seemingly distinct approaches: bus-branch and node-breaker. Historically, these philosophies have been treated as separate paradigms, each with its own intricacies and applications. However, thanks to GridCal’s innovative implementation, it becomes clear that these approaches are simply two sides of the same coin. In this article, we will explore how these modeling styles converge and why embracing a unified perspective simplifies power system analysis.
What Are Bus-Branch and Node-Breaker Models?
At their core, both models aim to represent the same physical power system network. In the CIM/CGMES grid modelling formats, Bus-branch modeling focuses on representing nodes with TopologicalNodes with no (or minimal) switching devices. On the other hand, node-breaker modeling utilizes models nodes with ConnectivityNodes, where switches and detailed configurations are explicitly represented. Despite these differences, the objective of both approaches is to capture the relationships between network nodes (buses) and their connections (branches).
The Case for Convergence
The perceived distinction between bus-branch and node-breaker has led to unnecessary complexity in power system modeling, often creating confusion for engineers transitioning between these philosophies. During GridCal’s implementation we realized that this famous divide was artificial, by showing that ConnectivityNodes and TopologicalNodes are interchangeable with proper processing.
Switches, commonly associated with node-breaker models, can also be seamlessly incorporated into bus-branch models. This has been historically recognized but discouraged. So, if the switches are not the differentiating point, what is? A unified perspective highlights that the two styles are not fundamentally different since they can be used to describe the same underlying network.
How GridCal Simplifies the Process
GridCal employs a topology processing methodology that bridges the gap between these modeling styles. It treats all nodes as part of a graph using one single node type (the Bus), defining relationships between buses and branches in a consistent abstraction. Rather than altering the original network data structure, GridCal creates snapshots, called NumericalCircuits, for topology processing. This ensures that the integrity of the original configuration is preserved while enabling detailed analyses. An efficient graph traversing algorithm identifies groups of buses that become the same topological place because of switching, demonstrating that node-breaker and bus-branch distinctions are non-existent when proper techniques are applied.
Why This Matters
Unifying these philosophies has significant implications for power system modeling. The current complexity in handling both node-breaker and bus-branch as distinct approaches hinders interoperability. A unified approach allows engineers to focus on core principles. Workflows become streamlined as tools like GridCal eliminate redundant complexity, enabling faster and more accurate simulations. This approach also ensures compatibility of power systems software (almost of any type) with standards like CIM/CGMES. A Bus before processing is a ConnectivityNode. A bus after processing becomes a TopologicalNode. Hence, in CIM/CGMES we should only model with connectivity nodes.
Debunking Misconceptions
A common misconception is that node-breaker models are inherently more detailed due to their inclusion of switches. However, we've experienced that this level of detail can be preserved in bus-branch models with appropriate processing. Similarly, the belief that bus-branch models lack flexibility is disproven by GridCal’s ability to handle switches and other complexities with a rather straight forward topology processing. This demonstrates that the two approaches are fundamentally equivalent.
The Takeaway
The bus-branch and node-breaker modeling philosophies are not distinct paradigms but rather two sides of the same coin. By adopting this view, power system engineers can transcend outdated divisions and embrace unified, efficient, and accurate modeling processes. This not only simplifies workflows but also ensures the alignment with global standards, bridging the gap between legacy and modern power systems models.
