Equivalent circuit of 8 kVA 400/120 V transformer

Method. The no-load (OC) test gives the shunt branch: $\cos\phi_0 = \frac{P_0}{V_0 I_0}$, $I_w = I_0\cos\phi_0$, $I_\mu = I_0\sin\phi_0$, $R_0 = \frac{V_0}{I_w}$, $X_0 = \frac{V_0}{I_\mu}$. The SC test gives the series branch: $Z = \frac{V_{sc}}{I_{sc}}$, $R = \frac{P_{sc}}{I_{sc}^2}$, $X = \sqrt{Z^2 - R^2}$. Values found on one side are moved to the other side by multiplying by the square of the voltage ratio.

Ratio: HV = 400 V, LV = 120 V, so to refer an LV value to HV multiply by $\left(\frac{400}{120}\right)^2 = 11.11$.

From OC test (on LV side): 120 V, 4 A, 75 W

$$\begin{aligned} \cos\phi_0 &= \frac{75}{120 \times 4} = 0.1563, \quad \sin\phi_0 = 0.9877 \\ I_w &= 4 \times 0.1563 = 0.625\ \text{A}, \quad I_\mu = 4 \times 0.9877 = 3.951\ \text{A} \\ R_0 (\text{LV}) &= \frac{120}{0.625} = 192\ \Omega, \quad X_0 (\text{LV}) = \frac{120}{3.951} = 30.37\ \Omega \end{aligned}$$

Referred to HV:

$$\begin{aligned} R_0 (\text{HV}) &= 192 \times 11.11 = 2133.3\ \Omega \\ X_0 (\text{HV}) &= 30.37 \times 11.11 = 337.5\ \Omega \end{aligned}$$

From SC test (on HV side): 9.5 V, 20 A, 110 W

The test is on the HV side, so the results are already referred to HV. (Rated HV current = 8000/400 = 20 A, so this is a full-load test.)

$$\begin{aligned} Z_{01} &= \frac{9.5}{20} = 0.475\ \Omega \\ R_{01} &= \frac{110}{20^2} = 0.275\ \Omega \\ X_{01} &= \sqrt{0.475^2 - 0.275^2} = 0.3873\ \Omega \end{aligned}$$

Equivalent circuit referred to HV side

 I1 ->        I0                 I2'
 o-----+--------+---[ R01 ]---[ jX01 ]---o
 +     |        |                        +
     [ R0 ]  [ jX0 ]                   load
 V1    |        |                       V2'
 -     |        |                        -
 o-----+--------+------------------------o
 All values referred to HV side:
 R0 = 2133.3 ohm, X0 = 337.5 ohm
 R01 = 0.275 ohm, X01 = 0.387 ohm

Answer: $R_0 = 2133.3\ \Omega$, $X_0 = 337.5\ \Omega$, $R_{01} = 0.275\ \Omega$, $X_{01} = 0.387\ \Omega$, $Z_{01} = 0.475\ \Omega$ (all referred to HV).