3 Winding Transformer

[RANS20]

How Can i get the impedance pattern of LV1-HV=12%, LV2-HV =12% and LV1-LV2= 24%, where LV1, LV2 and HV are 4.16kv, 13.2 kV and 138 kV.Transformer MVA for LV1, LV2 and HV is 12MVA, 8 MVA and 20 MVA. what winding scheme should I adopt to get this impedance pattern and what are the problems we can face. HV winding have DETC with +/- 2 taps @2.5% also , and 4.16 KV have LTC with +/-10% with 0.625%.

 

[argotier]

May I ask what is your role in this?

Are you the trx manufacturer? Or are you drafting a specification for purchase or something like that?

If is the first, not knowing how to arrange the windings to achieve those impedances might be a bad sign.

If is the latter, you don't need to worry about the winding arrangement, just specify the impedances and the manufacturer will know best.

Possible problems might arise if this transformer is meant to be working in parallel with an existing unit. LTC regulating winding relative placement will affect the impedances in upper and lower positions. So if paralleling is a possibility, you will need to specify also the impedances of the existing transformers in LTC upper and lower positions, so the new unit can match them.

It's an unusual impedance pattern but should be doable. I've only seen something similar in some rather specific transformers, not the usual substation type.

Hope it helps.