To model a Zig-Zag Grounding Transformer in ETAP you can use a two winding transformer connected as (solidly grounded).

During normal operation, the current flowing in a zig-zag transformer is the magnetizing current which is very small compared to the normal operating current and hence is negligible.

Under a line-to-ground fault the current flowing to the ground through the zig-zag transformer is equal to the rated neutral current, if 100% line-to-neutral voltage is applied.

A Zig-Zag Grounding Transformer can be represented in ETAP by a transformer with the delta side bus not connected to any load (Bus2).

To calculate the parameters of the Zig-Zag transformer, you may use the following equations.

Let the ratings of the Zig-Zag transformer you want to model be:

The equivalent parameters of transformer will be:

Where is the transformer Zero sequence impedance.