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Warning 121 | [Various software] | SCR= or XR= set on a branch that is not connected to a swing or reference bus


Relevant software:

PSS®E
PowerFactory


Emitted message:

A command or part of a command is calculating the SCR or XR for a line/branch. Neither end of this line/branch is a swing or reference bus. This could cause incorrect point of connection fault levels to be used in your model - which could cause poor benchmarking with other software packages.

Description:​

This warning is raised when attempting to set the Thevnin equivalent impedance from the specified Short Circuit Ratio (SCR) or X/R ratio (collectively the fault level) for a line or branch where neither end is connected to a swing or reference bus.

danger

This warning indicates there may be an issue in your PSS®E and/or PowerFactory model which may cause the fault level applied by the gridmo Engine to be lower than the fault level requested.

For example, the below command sets the impedance of the branch between bus 1001 and bus 1000 to correspond to a fault level of 3 SCR and 2 XR.

SET, LINE=1001->1000#1, STATUS=IN, SCR=3, XR=2
Diagram showing SCR calculation with non-reference branch

If bus 100 is not a swing or reference bus, there may be additional impedance between the slack/reference bus and the point of connection, which may result in the fault level applied by the gridmo Engine being lower than the fault level requested.

Potential issues:​

  • If there is any additional impedance between the slack/reference bus and the point of connection, the fault level applied by the gridmo Engine may be lower than the fault level requested.
  • Benchmarking with other software packages may show discrepancies due to different fault levels being used.

Potential fixes:​

  • Ensure that one end of the monitored branch or line is connected to a swing/reference bus in your model.
  • If neither end is currently a reference bus, consider modifying your model to designate an appropriate bus as the reference.
  • For more complex networks, you might need to define an equivalent circuit that properly represents the system strength at the point of connection.