Three-phase, three-winding transformer parameters

How to calculate the following values in a three-phase, three-winding transformer? I need to model this transformer in MATLAB/Simulink (attached block from Simulink).

1. Individual resistances (R1, R2, R3) of each winding?

2. Individual leakage inductances (L1, L2, L3) of each winding?

3. Overall magnetizing resistance and inductance (Rm, Lm)?

The following values are given on the transformer nameplate.

Power = 12.75kVA

Primary Winding: Wye, 460V, 16A

Secondary Winding: Wye, 11.5V, 320A

Tertiary Winding: Delta, 11.5V, 320A

Percentage impedance = 5.2%

Answer 1

[Kothuri]

Hi ,

I understand that you would like to know how the Individual resistances (R1, R2, R3) of each winding, Individual leakage inductances (L1, L2, L3) of each winding and Overall magnetizing resistance and inductance (Rm, Lm) are calculated based on the name plate details.

• The resistances of each winding can be calculated based on the percentage impedance and the rated current for each winding.
• The formula for resistance in each winding is: ​ R = ZxVrated/Irated​

where ( Z ) is the percentage impedance (in decimal form), ( Vrated ) is the rated voltage, and ( Irated ) is the rated current for the winding.

• Leakage inductance can be calculated using the same percentage impedance, considering that the impedance is a combination of resistance and reactance.
• The formula for leakage inductance is: L = (ZxVrated)/( ωxIrated) ​​

where (ω) is the angular frequency of the system (ω = 2πf ), where ( f ) is the frequency).

• Overall Magnetizing Resistance and Inductance (Rm, Lm) values are typically derived from open-circuit tests and are not directly calculable from the nameplate data. However, they can be estimated based on typical values for transformers of similar size and construction.

You can refer the below documentation link for more info on Three-phase, three winding transformers.

https://www.mathworks.com/help/sps/powersys/ref/threephasetransformerthreewindings.html