Q: We sometimes provide Thevenin equivalent fault impedances that are calculated in OneLiner to others for use in dynamic stability simulations.  How are these impedance values impacted by the presence of IBR models in the OneLiner network model?

A:   Since the Thevenin equivalent calculations do not strictly hold for a nonlinear model, the Thevenin impedances reported by OneLiner will not account for the nonlinear models in the system.  Thevenin impedances near current limited generator models may be smaller than expected, while those near other IBR models may be larger than expected.  The x-over-r ratio of the impedances can be affected as well.