Ynynd Transformer Z0

[cyriousn]

From reading the excerpt below from IEC 60076-8, I'm interpreting Z0 to be .85-0.9 the value of Z1. Is this a correct interpretation? I've recently seen utilities/ISOs requesting Z0 data on transformer during the interconnection studies and I can't seem to get a good understanding on this topic.

"The magnetizing impedance Zm which is also indicated in figure 11, is usually neglected in calculations for this winding combination. It is accepted that the zero-sequence impedances of the diagram differ somewhat from values measured with positive sequence current. The difference depends on the arrangement of the windings with respect to each other and usually stays within 10 % to 15 %"

 

[davidbeach]

For a 3-phase core type transformer, yes. For shell type, or for banks of three single phase transformers, no. In those cases assume Z0 = Z1. But always, if possible, use measured Z0 values rather than rules of thumb.

 

[cyriousn]

For a 3-phase core type transformer, yes. For shell type, or for banks of three single phase transformers, no. In those cases assume Z0 = Z1. But always, if possible, use measured Z0 values rather than rules of thumb.

Thank you. I recently read that shell type transformers are more energy efficient and have better fault duties thus more likely to be specified. I have no real world data points on this so I was wondering if you had any insight that could be shared?

 

[davidbeach]

I don't think I've encountered a new shell type in the 18 years I've been in the utility business.

 

[cyriousn]

I don't think I've encountered a new shell type in the 18 years I've been in the utility business.

Interesting, I guess that might be why all the reference data I see has the Z0 lower than the Z1.