Q:   Why does a CIR model shut down on low or high voltage when the voltage appears to be within the acceptable range?

A:   The CIR shutdown conditions are determined based on the model parameters and the minimum/maximum individual phase voltages at its terminal bus.  Even if the CIR minimum voltage parameter is specified as 0.0 (low voltage shutdown occurs at or below the setting), if a CIR terminal bus voltage magnitude becomes very small (approximately zero) on any phase, the CIR model will shut down.  Additionally, if any CIR terminal phase voltages exceed the upper limit specified in the model parameters, the CIR model will shut down.  For example, this is often seen in a weakly grounded system during 1LG faults, where the unfaulted phase voltages may exceed the high voltage limit setting of the CIR model.