How to find zero sequence impedances for 3winding transformers 1

[wonderchi]

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

 

[ausphil]

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

 

[KJvR]

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.

 

[cuky2000]

I hope the enclose info could help:

http://cuky2000.250free.com/Three_Winding_Transf.gif

http://cuky2000.250free.com/Transf_Three_Winding_2.jpg

 

[KJvR]

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).

 

[cuky2000]

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