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Warning 109 | [PSS®E] | SMIB Distance Factor with low source impedance


Relevant software:

PSS®E


Emitted message:

The SMIB Distance Factor (dfactor) specified in this Node is not 0% or 100% - meaning it is faulting between the two buses - but the source impedance is extremely low - you may see an unexpected voltage change in your simulation result due to the creation of infinite branches
tip

If your PSS®E Dynamic results appear stable you can ignore this warning.

Description:​

This warning indicates that:

  • A fault is being applied using a SIMPLEFAULT Command
  • The Distance factor field is not equal to 1 (meaning the fault is not applied at the generator's connection point)
  • The short circuit ratio (SCR) is extremely high.

This can force the gridmo Engine to create ideal branches in PSS®E, which may lead to numerical instability in your simulation results.

Possible impact:​

  • We've seen cases where extremely low line impedances can cause numerical instability in static and dynamic simulations in PSS®E, such as large spikes of reactive power during dynamic simulations.

See PSS®E warning 108 for more details on the effects of low line impedances.

Potential fixes:​

  • Avoid setting Distance factor to a value other than 1 when completing studies with a very high short circuit ratio.
    • Instead, consider setting Distance factor to 1 and using a non-zero FZ= value to apply a non-bolted fault.
    • This approach avoids the creation of ideal branches which should remove the instability.