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See Also: Transformer Modelling

Modelling a Tertiary Winding Transformer:

An equivalent positive and zero sequence circuit is required as indicated below:

 

The first step :

Obtain the leakage impedance between:

Primary (p) and Secondary (p) Zps

Primary (p) and Tertiary (t)     Zpt

Secondary (s) and Tertiary (t)  Zst

 

These values should be available from the transformer manufacturer, otherwise applying a test voltage to one of the windings, shorting the second winding and opening the third winding can complete a test. Repeat for the other windings to obtain the required impedance.

 

To obtain Zp, Zs and Zt the following relationships exist:

 

The second step

Obtain the neutral impedance of:

Primary (p) and Neutral (n)     - Znp

Secondary (s) and Neutral (n) - Zns

Tertiary (t) and Neutral (n)     - Znt

 

The zero sequence impedance then is as follows:

For a grounded star winding, use Znp and/or Zns and/or Znt as applicable.

For an ungrounded star or a delta winding, ignore the neutral impedance.

The third step Create three transformers with above data.