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4 kVA 200/400 V test parameters

Short answer

Referred to LV side: Ro=571.4 Ω, Xo=278 Ω, R01=0.15 Ω, X01=0.477 Ω (Z01=0.5 Ω).

A 4-kVA, 200/400 V single phase transformer has following test results: O.C Test: 200 V, 0.8 A, 70 W S.C Test: 20 V, 10 A, 60 W Obtain equivalent circuit parameters of the transformer refer to L.V side.

Given: 4 kVA, 200/400 V. OC test: 200 V, 0.8 A, 70 W. SC test: 20 V, 10 A, 60 W.

Assumptions: the OC test voltage of 200 V shows it was done on the LV side. The rated HV current is 4000/400 = 10 A, equal to the SC current, so the SC test was done on the HV side. K = 400/200 = 2.

Shunt branch (LV side)

cos φ0 = 70/(200 × 0.8) = 0.4375
Iw = 0.8 × 0.4375 = 0.350 A
Iμ = √(0.8² − 0.35²) = 0.719 A
Ro = 200/0.350 = 571.4 Ω
Xo = 200/0.719 = 278.0 Ω

Series branch

On HV: Z02 = 20/10 = 2.0 Ω; R02 = 60/10² = 0.6 Ω; X02 = √(2² − 0.6²) = 1.908 Ω.

Refer to the LV side by dividing by K² = 4:

Z01 = 2.0/4 = 0.500 Ω
R01 = 0.6/4 = 0.150 Ω
X01 = 1.908/4 = 0.477 Ω

Equivalent circuit (LV side)

        R01=0.15Ω   X01=0.477Ω
 o──┬────┬───/\/\/───────(((────────o
    │    │                          
 571.4Ω 278.0Ω                  load
    │    │                       V2'
 o──┴────┴───────────────────────────o

Answer: Ro = 571.4 Ω, Xo = 278 Ω, R01 = 0.15 Ω, X01 = 0.477 Ω (Z01 = 0.5 Ω), referred to LV side.

✓ Answer checked by Claude Opus 5.5 (high effort)

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