ETAP Transformer Modelling 1

[Amex12]

I am trying to model a Wye(ungrounded)/Wye(grounded)/buried delta tertiary transformer in ETAP. The HV side is the source of fault current and is ungrounded as specified. When I model it as a two winding transformer, I am able to select a checkbox for buried tertiary. However, when I place a L-G fault on the Wye(grounded) LV side, I see no ground fault current.

However, when I model this as a three winding transformer with the buried delta as the third winding, when I place a L-G fault on the Wye(grounded) LV side, I see ground fault current.

What is the correct approach here?

 

[davidbeach]

It seems that a three winding transformer needs to be modeled as a three winding transformer.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Amex12]

Thanks @davidbeach, but would it be fair to say that no fault current would be generated for a L-G fault on the LV side without the buried delta tertiary corner grounded winding?

 

[davidbeach]

Tertiary does not need to be grounded for there to be LV SLG fault current. It merely needs to be. Grounded is good, for other reasons, but irrelevant for fault current.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[beyond86]

The reason is that parameters "Buried delta winding" for two winding transformers use only in unbalanced load flow analysis. It doesn't take into account when you use short circuit calculation cases.
You should use three winding transformer model for SC calculation.