The general line type (TypLne) is based on impedance values and can be defined with or without the neutral wire. Depending on the use case, the neutral can be modelled either explicitly (3 phases + neutral) or as part of the zero-sequence impedance in a 3 phase model. The following FAQ describes the two approaches as well as defining the corresponding input parameters.

• 3 phase system: The earth return path (e.g. via neutral, via earth, via earth/neutral, via sheath etc.) can be modelled via the zero-sequence impedance. The impedance has to be specified for a particular earth return path which is considered in the model. Compared to the 4 phase system, only one earth return path can be considered.
• 4 phase system: The neutral is modelled explicitly and therefore different earth return paths can be considered. The zero-sequence impedance contains the return path without the neutral (e.g. via earth, via sheath, via PE wire etc.). Compared to the 3 phase system, the neutral has to be extracted from the zero sequence impedance and modelled explicitly with the corresponding parameters.

The attached pdf document “Calculation parameter 4 wire system.pdf” contains the modelling description of the two approaches. As an example, the cable type “NYCWY 4x70/35” is modelled with/without explicit neutral wire.

The attached Excel sheet “NYCWY” contains the corresponding hand calculations including short-circuit calculations in case of a single phase to ground fault.

The attached PFD file “NYCWY_4x70_35.pfd” contains the project in PowerFactory where the cable models as well as the short-circuit calculation can be verified.