Why is the calculated zero sequence impedance a negative value?

Zero Sequence Error Message

Error message: "The calculated zero sequence impedance is negative."

This involves the entry of single-line-to-ground short circuit contribution data for the Utility component. PTW uses the three-phase fault data and the single-line-to-ground fault data to calculate the positive, negative- and zero-sequence impedances.

Solution: Double-check the three-phase fault data and the single-line-to-ground fault data entered in the Utility component editor. Most likely the single-line-to-ground fault data entered is too high. See section 4.3.5 of the DAPPER reference manual for more details on this error message and how to correct it.