The following results are obtained on a 40 K.V.A, 2400/120 V transformers - OC test: 120 V, 9.65 A and 396 W (L.V side) - SC test: 92V, 20.8A and 810W (H.V side) - Calculate the parameters of approximate equivalent circuit referred to H.V. side -

Equivalent circuit constants

From OC test (meters are connected on L.V. side, i.e. secondary)

Given: W1= 396W

V2= 120 V

I0= 9.05 A

$\cos ф0 = Wi/ V2 * I10 \\ = 396/ 120 * 9.65 = 0.34 \\ ∴ \cos ф10 = 0.34 \\ ∴ \sin ф0 = \sin (\cos-1(ф01)) \\ = 0.94$

$I1w= I10 \cos ф01= 9.65 * 0.34 = 3.28 A \\ R10= V2/I1W = 120 /3.3 = 36.36 π \\ I1M= I10 \sin ф01 = 9.65 * 0.94 = 9.07 A \\ X10 = V2/I1u = 120/9.07 = 13.23 Ω \\ K= 120/2400 = 0.05 \\ R0 = R10 / K2= 36.36 / (0.05)2 = 14.54 Ω \\ X0= X10/K2 = 13.23/ (0.05)2 = 5.29 K Ω$

From SC test (connected on primary)

$WSC= 810 W VSC= 92V ISC = 20.8A \\ Zo1= VSC/ISC = 92/20.8 = 4.42 Ω$

$R01 = WSC/ISC = 810/ (20.8)2 = 1.87 Ω \\ V01 =\sqrt{(Z01) ^2 – (R01) ^2 } \\ = (4.42)^2 – (1.87)^2 \\ = 4Ω$