High-tertiary impedance design change from 12% to 26% 1

[EddyPach]

Can somebody explain what would be the effect of changing the H-Y (high to tertiary) impedance in a 120/160/200 MVA, 260-144/25 kV, three phase autotransformer, from 12% (required) to 26% (per design). The H-X impedance is 5%.
Thanks for the info.

 

[prc]

The question is not clear.Can you explain?What is meant by "required" and "designed"?Also indicate T-X impedance also on both cases.Hope H-Ximpedance remains the same.

 

[EddyPach]

A corp. requires a 120/160/200 MVA auto Xfr with H-X=5% and H-Y=21% requirements. However our engineering can only comply with the H-X at 5%, and only provide H-Y = 36% impedance instead of 21%. My questions is what can possibly change with our deviation? Does it matter if the tertiary is buried or if it is loaded? If so, why should that be?

 

[prc]

If the tertiary is buried it will not matter at all ,but in a way better as the circulating current in tertiary will be reduced.But if it is aloaded tertiary ,regulation at tertiary terminals will be higher as the T arm of the circuit will have higher impedance.