Transformer Impedance Table. Table 3 2 1 typical transformer impedances tables a and b reprinted with permission from electrical transmission and distribution reference book abb power t d co raleigh nc. Z x rt rated transformer secondary current calculated.
I xfrmr amps primary short circuit kva. X1 z1 x sin arctan x r1 r1 x1 x r1 transformer impedance calculation zt. 1ø transformer kva rating secondary volts pad mounted overhead impedance fault current amps impedance fault current amps 15 120 240 1 78 1 30 7 006 4 808 2 13 1 55 5 876 4 032 25 120 240 1 78 1 30 11 677 8 013 1 92 1 40 10 843 7 440 37 5 120 240 2 11 1 50 14 819 10 417 2 09 1 49 14 919 10 487 50 120 240 2 05 1 44 20 346 14 468 1 99.
These values are for three phase liquid filled self cooled transformers.
It s a tested value that the manufacturers do for power distribution transformers and is used in the fault current calculation. Z x rt rated transformer secondary current calculated. The impedance is measured in ohms and can include resistance r inductive reactance xl and capacitive reactance xc. This is important for coordinating over current protection devices.
