Help with Transformer Impedance Terms

[holmsey]

Hi All,

I'm trying to complete a generator interconnection application to send into a utility company (United Illuminating) in Connecticut. They have asked for some information for the generator step up transformer but unfortunately I'm not familiar with the terminology they are using. Here is what they are looking for:

Transformer Positive-Sequence Short Circuit Impedances (pu): Zps= ????, Zpt= ????, Zst= ????
Transformer Zero-Sequence Impedances (pu): Zpm0= ????, Zsm0= ????, Zmg0= ????​

I was hoping someone could provide me with some guidance as to what these terms (Zps, Zpt, Zst, Zpm0, Zsm0, and Zmg0) mean or at least point me in the right direction.

Thanks

 

[magoo2]

For the positive sequence impedances, they are describing those for a three-winding transformer.
p is primary
s is secondary
t is tertiary

We normally use a two winding transformer, so you would only have Zps.

I'm not sure what their zero sequence impedances stand for. I am more used to using the same letters for positive and zero sequence impedances, but just labeling them as positive and zero sequence respectively.

 

[davidbeach]

The zero sequence is for a T model of a three winding transformer, m is Middle, the node of the T.

 

[wbd]

It looks like you have a transformer with tertiary windings:
Zps - impedance between the primary and secondary windings
Zpt - impedance between the primary and tertiary windings
Zst - impedance between the secondary and tertiary windings

The other terms I have not seen before

 

[stevenal]

Look for the test report from the transformer manufacturer.

 

[holmsey]

Thank you all.

It sounds like my confusions stems from my lack of experience with three winding transformers which are not too common at the facility distribution level.

I intend to use a two winding transformer so it looks like the other values really aren't applicable to my situation.