Transformer Impedance Calculation from Test Data
Transformer Impedance Calculation from Test Data
(OP)
Hi,
I'm trying to determine the appropriate way to represent 3-winding Delta transformer to its equivalent Wye representation. The given data were: Primary : Secondary voltages, its MVA rating, MW loss, and %Z. I saw an old note in the past which indicates the calculated resistance as %R = MW loss * 100 / rated MVA. I didn't see any logic in this resistance calculation. If you have any links or advices to the above subject, please let me know. Thanks.
I'm trying to determine the appropriate way to represent 3-winding Delta transformer to its equivalent Wye representation. The given data were: Primary : Secondary voltages, its MVA rating, MW loss, and %Z. I saw an old note in the past which indicates the calculated resistance as %R = MW loss * 100 / rated MVA. I didn't see any logic in this resistance calculation. If you have any links or advices to the above subject, please let me know. Thanks.






RE: Transformer Impedance Calculation from Test Data
%R = I^2 R * 100 / (I^2 Z)
I^2 * R = the resistive losses
I^2 * Z = MVA rating
Expressing the losses as a % of the MVA rating is what the formula does. It is common to all transformers - be they 2 winding, 3 winding or more.
A test report should give you the %Z between pairs of windings. With a 3 winding transformer, let's call the terminals H, L and T (high, low and tertiary).
Get 3 values from test report:
Z_H-L = impedance between H and L
Z_H-T = impedance between H and T
Z_L-T = impedance between L and T
Z_H = 1/2 (Z_H-L + Z_H-T - Z_L-T)
Z_L = 1/2 (Z_H-L + Z_L-T - Z_H-T)
Z_H = 1/2 (Z_H-T + Z_L-T - Z_H-L)
Looks better if you can use subscripts, but this should give you what you want. These impedances, Z_H, Z_L and Z_T are the wye equivalent values.
RE: Transformer Impedance Calculation from Test Data
Truly appreciate for your help. Have a great day.
RE: Transformer Impedance Calculation from Test Data