Understanding Area Balancing Area Interchanges Understanding Area Balancing

Overview What is an area interchange? Why should we care? How does power flow programs use them? Simple System When things go wrong… Additional References

What is an area interchange? Starting with the idea of a slack (swing) bus: In electrical power systems a slack bus (or swing bus), is used to balance the active power |P| and reactive power |Q| in a system while performing load flow studies In a power system model with multiple balancing areas, there becomes multiple pockets of load/generation/losses to balance

What is an area interchange? The power flow scheduled between areas must be accounted for during this balancing, these scheduled power flows are known as area interchanges For any balancing area within a power flow case the following must hold true: total gen - total load - total losses = scheduled tie-line flow – swing gen

Interchanges (Imports/Exports) + Slack Generator Generation Loads

Why should we care? The interchanges or area swing generator must make up the balance in each area. If the interchange is not reasonable based on load/gen patterns, the swing machine may exceed physical limitations (Pmin/Pmax/Dynamic) Unrealistic (actual generator in system) Solution issues from excessive MW output

How does Power flow programs use them? Classical area interchange option: In this solution option, the net interchange is controlled by adjusting the outputs of the area swing generators to bring the area net interchanges to their scheduled value. From PSLF manual:

How does Power flow programs use them? With Area Interchange Control enabled, the software will enforce interchange schedules by adjusting the local swing generators With Area Interchange Control disabled, the software will rely on the system swing bus for balancing efforts

Simple System Gen=45 Load=100 Swing=5 Interchange=-50 Gen=90 Load=100

Simple System Increased Interchange Gen=45 Load=100 Swing=-5

Simple System Decreased Interchange Gen=45 Load=100 Swing=-5

Simple System Is this realistic? Or this? Gen=45 Load=100 Swing=-5 Interchange=-60 Gen=90 Load=100 Swing=20 Interchange=10 Gen=125 Load=100 Swing=25 Interchange=50 Or this?

When things go wrong… 𝐴𝑟𝑒𝑎 𝐼𝑛𝑡𝑒𝑟𝑐ℎ𝑎𝑛𝑔𝑒𝑠 =0 Area without swing (or offline) – software must allocate resources from the system swing, resulting in odd case behavior and possible divergence Area Interchanges in case do not sum to zero – system swing will make up slack, causing extra generation in the case. 𝐴𝑟𝑒𝑎 𝐼𝑛𝑡𝑒𝑟𝑐ℎ𝑎𝑛𝑔𝑒𝑠 =0

Additional References Page I8-19: http://www.powerworld.com/files/TrainingI08GeneratorAreaMWControl.pdf PowerWorld Manual PSLF Manual PSS®E Manual

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