Skip to main content

Warning 162 | [PSS®E] | Multiple swing buses detected


Relevant software:

PSS®E


Emitted message:

Multiple swing buses detected in case file

Description:​

This error indicates that the PSS®E case file (.sav) loaded for the simulation contains more than one swing bus (also known as a slack bus, reference bus or type 3 bus).

In a standard power flow analysis, there must be exactly one swing bus. This bus serves as the reference for voltage angle and balances the total active and reactive power in the system. Having multiple swing buses makes the power flow problem mathematically indeterminate - though not necessarily invalid, as the second swing bus may be in an electrtically isolated part of the newtork (for example in the Australia NEM wide area PSS®E models, there are typically two swing buses - one in New South Wales and one in Tasmania).

danger

If this Node is a Single Machine Infinite Bus (SMIB) test, then this warning indicates that the following may not work correctly, or be different to the specified value:

  • Playback of voltage, frequency and/or angle.
  • Short circuit ratio (fault level).

Possible impact:​

  • The gridmo Engine will proceed with the simulation, however the playback of voltage, frequency and/or angle may not work correctly, or be different to the specified value.
  • The short circuit ratio (fault level) may not be calculated correctly.

Potential fixes:​

  • Review PSS®E Case File: Open your .sav file in PSS®E and examine the bus data.
  • Identify and Modify Swing Buses: Locate all buses with type code of 3 - if there are multiple, ensure they are electrically isoalted. If electrically connected, select one bus to be the swing bus and change the type code of the other bus to 2 (generator) or 1 (load).
  • Save and Re-run: Save the corrected case file and re-run the simulation in gridmo.