---
title: "4 kVA 200/400 V test parameters"
subject: "Electrical Machine"
chapter: 2
key: "semester_4/electrical_machine:transformer-4kva-200-400-lv-side"
source: https://www.bctengineer.com/q/semester_4/electrical_machine/transformer-4kva-200-400-lv-side
site: BCT Engineering
---

# 4 kVA 200/400 V test parameters

Electrical Machine · Chapter 2: Transformer

- Asked in: 2073 Magh, 8 marks
- Video: [Transformer OC test and SC test problems | effeciency, voltage regulation calculations](https://www.youtube.com/watch?v=aB2j_Fqd4zo) — The PiSquare Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/electrical_machine/transformer-4kva-200-400-lv-side
- Whole chapter: https://www.bctengineer.com/md/semester_4/electrical_machine/chapter-2

## Question

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.

## 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).

## Answer

**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)
```text
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:
```text
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)
```text
        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.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How can we tell the SC test was done on the HV side?
   A. It has a lower voltage
   B. The SC current 10 A equals rated HV current 4000/400
   C. The wattmeter reads 60 W
   D. The OC test was on LV
   Answer: B. Rated HV current is 10 A, matching the SC test current. (Key point: Identifying test side)

2. What is the magnetising current Iμ?
   A. 0.35 A
   B. 0.8 A
   C. 0.719 A
   D. 0.45 A
   Answer: C. Iμ = sqrt(0.8² − 0.35²) = 0.719 A. (Key point: Iμ)

3. What are R01 and Z01 referred to the LV side?
   A. 0.6 Ω and 2.0 Ω
   B. 0.15 Ω and 0.5 Ω
   C. 2.4 Ω and 8 Ω
   D. 0.3 Ω and 1.0 Ω
   Answer: B. R02 = 0.6, Z02 = 2.0 divided by K² = 4 gives 0.15 and 0.5 Ω. (Key point: Series branch referral)

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