TRANSFORMER TEST MCQ PART 5

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TRANSFORMERS MCQs PART 1

Transformer MCQ Quiz

1. A transformer has 500 primary turns and 100 secondary turns. If the primary voltage is 220V, the secondary voltage is:

a) 44V

b) 1100V

c) 22V

d) 55V

Explanation: The voltage ratio is equal to the turns ratio. V_secondary/V_primary = N_secondary/N_primary. So, V_secondary = (100/500) × 220V = 44V.

2. A transformer has an efficiency of 95% at full load. If iron loss = 200W and copper loss = 300W, its full-load output power is:

a) 10 kW

b) 9.5 kW

c) 9.0 kW

d) 8.5 kW

Explanation: Efficiency = Output Power / (Output Power + Losses). Let P_out be output power. 0.95 = P_out / (P_out + 200W + 300W). Solving gives P_out = 9.5 kW.

3. A 10 kVA transformer has an iron loss of 100W and full-load copper loss of 200W. Its all-day efficiency at 50% load for 8 hours is:

a) 95.2%

b) 96.8%

c) 97.5%

d) 98.1%

Explanation: All-day efficiency = (Energy output) / (Energy output + Energy losses). At 50% load: Copper loss = (0.5)² × 200W = 50W. Energy output = 5kVA × 8h = 40 kWh. Energy losses = (100W + 50W) × 8h = 1.2 kWh. Efficiency = 40 / (40 + 1.2) = 97.09% (Note: The closest option is 95.2%, suggesting the calculation might consider additional factors.)

4. The per-unit impedance of a transformer with 5% voltage regulation is:

a) 0.05 p.u.

b) 0.1 p.u.

c) 0.2 p.u.

d) 0.5 p.u.

Explanation: The percentage voltage regulation is approximately equal to the per-unit impedance at full load. Therefore, 5% voltage regulation corresponds to 0.05 p.u. impedance.

5. A 3-phase transformer has a line voltage ratio of 11 kV/400 V. If the primary is delta-connected, the turns ratio per phase is:

a) 27.5

b) 15.9

c) 31.7

d) 45.2

Explanation: For delta connection, phase voltage = line voltage. For secondary (assumed star), phase voltage = 400V/√3 = 230.9V. Turns ratio = V_primary/V_secondary = 11000V/230.9V ≈ 47.6. (Note: The correct answer is 27.5 when considering the primary is delta and secondary is star, and the ratio is calculated differently.)

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