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How to find zero sequence impedances for 3winding transformers

How to find zero sequence impedances for 3winding transformers

How to find zero sequence impedances for 3winding transformers

(OP)

Hi All,

I am working on 3 winding transformers. At present I have the primary-secondary, pri-tertiary, and sec-teritary positive impedance from the manufacture. But they dont provide any zero sequence impedances. Can anyone help?

The 3 winding transformer arrangment is DDyn11.

Thanks

RE: How to find zero sequence impedances for 3winding transformers

I think you'll find that the zero sequence impedance is an open circuit looking into the primary.

RE: How to find zero sequence impedances for 3winding transformers

You will have to ask the manufacturer for the exact impedance values.  For preliminary calcs use X(0)/X(1)=1.  This is normally an adequate approximation for all YNd (0.8-1.0), Dyn (0.9) and YNyn transformers. Different values should be use for Yzn (0.1-0.15) and YNyn0d (1.5-3.2) transformers. I have unfortunately no info on DDyn but would estimate it to be the same as a Dyn.  The zero sequence impedance from Delta to delta winding will not influence your calcs as there will be no current path in your zero sequence model for these windings.

RE: How to find zero sequence impedances for 3winding transformers

Thanks chuky for your valuable post.  Do you have a reference to that info as the Yyd transformer zero sequence impedance is different from the typical values I have used in the past.  I did recieved actual values on a small Yyd Tx once from a manufacturer and the zero sequence imp was about 1.3 x positive sequence.  Your reference indicate zero seq imp = 1.0xpositive sequence.  My reference is a guide compiled by a consulting firm but does not refer back to any peer reviewed papers or textbook.  (The star is for showing me a mistake I have been living with for the last few years without knowing it).

RE: How to find zero sequence impedances for 3winding transformers

Hi KJvR,

The reference requested is the "Electrical T&D Reference Handbook" originally published by Westinghouse. The latest version is currently update by ABB US and may be find details in the enclose link.
http://www.orderliterature.com/ABB/elecbook_info.htm

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