The Fast Trans range of transformers, which are liquid filled free breathing distribution transformers, covers following kVA ratings and the percentage impedance guarantees for each rating as detailed below :-

See attached pdf references for both copper and aluminum windings.

315kVA           Percentage impedance guarantee = 4.75% at a Reference Temperature of 75ºC, subject to IEC 60076 Tolerances of ±10%
500kVA           Percentage impedance guarantee = 4.75% at a Reference Temperature of 75ºC, subject to IEC 60076 Tolerances of ±10%
800kVA           Percentage impedance guarantee = 4.75% at a Reference Temperature of 75ºC, subject to IEC 60076 Tolerances of ±10%
1000kVA         Percentage impedance guarantee = 4.75% at a Reference Temperature of 75ºC, subject to IEC 60076 Tolerances of ±10%
1250kVA         Percentage impedance guarantee = 5.0% at a Reference Temperature of 75ºC, subject to IEC 60076 Tolerances of ±10%
1500kVA         Percentage impedance guarantee = 5.5% at a Reference Temperature of 75ºC, subject to IEC 60076 Tolerances of ±10%
2000kVA         Percentage impedance guarantee = 6.0% at a Reference Temperature of 75ºC, subject to IEC 60076 Tolerances of ±10%