3-winding transformer impedance

[budhiman]

Hello All,
Attached is the link of three winding rectifier transformer. It has an impedances shown for two kVA bases (8000 and 10000). Per my understanding, the impedance is higher for higher kVA and lower for lower kVA rating. But the nameplate shows the other way. Why is the impedance for a higher kVA lower as shown in the attached image?

 

[davidbeach]

Because the higher kVA rating is also at a lower voltage ratio. 8MVA @ 12470:520 and 10MVA @ 12470:640. Not the same connections, not the same transformer.

 

[HamburgerHelper]

I can't see the attachment but if you are rating something on a higher base, it's pu impedance will be higher as well.

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If you can't explain it to a six year old, you don't understand it yourself.

 

[davidbeach]

Different configurations of the transformer that give different ratings, not just a simple case of multiple ratings for the same configuration. Given the reconfiguration there's not much you can say about one impedance knowing the other one.