How to find buried delta winding current using symmetrical components

[chuckd83]

I have a Yg-D-Yg three winding transformer used on a wind farm collector station. It is a buried delta and I'm trying to find the winding current in the delta for a primary or secondary ground fault. I used symmetrical components to find current for a primary ground fault (see attached from the Westinghouse book). Is there a way to use this to find the current that will be flowing through the delta windings during the fault?

I can use a current divider to find the zero sequence current through the ZL0 component, but don't know how to translate that to actual current in the delta winding. Thanks for any help.

Zp = primary source impedance (utility)
Zs = secondary source impedance (wind farm)

 

[chuckd83]

My notes showing the sequence network interconnection for a fault on the primary.

 

[waross]

You need to know the impedance of the primary to the delta. Current in the delta will be limited by three times the impedance.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[chuckd83]

You need to know the impedance of the primary to the delta. Current in the delta will be limited by three times the impedance.

That is given by Zpt% in the Westinghouse equations.

 

[prc]

Please see attached paper- bit old but with simplified calculations for current in stabilizing delta.

 

[jwatty]

I'm not sure your notes are correct. If you have some short circuit software, fault the highside and show currents in per unit. The tertiary current, in per unit, will be the difference between the I0 coming into the lowside and I0 going out the highside. Scale this per unit current by your base current (model MVA base / [tertiary L-L kv x sqrt(3)]. Divide this by sqrt(3) since you're inside the delta, and you'll have the I0 current flowing in the delta.

If you're doing hand calcs and model the transformer as a T model, the delta current (in per unit) will be whatever is flowing in the winding from the fictitious tap to neutral.