Winding Impedances

In some cases, the impedances obtained from short-circuit tests (Z12, Z13, Z23) provide a T-equivalent model with negative parameters (Z1, Z2, Z3). This often occurs in the case of transformers with a winding of less power (internal tertiary winding in delta for example).

EMTP supports negative values but may cause numerical problems depending on the parameters of the surrounding elements. Therefore, it is recommended to consider positive values for all the impedance elements. Here is an example of a short-circuit test result that gives negative values.

HYPERSIM does not accept negative values for resistors, inductors and capacitors. They will be automatically replaced by null values. Therefore: