Transformers worksheet with answers

Free printable Transformers worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

An ideal transformer has 100 turns on its primary winding and 400 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 400V₁ = 690 V

V₂ = V

2.Easy

An ideal transformer has 120 turns on its primary winding and 1200 turns on its secondary winding. The primary is connected to a 240 V AC supply. Find the secondary voltage V₂.

N₁ = 120N₂ = 1200V₁ = 240 V

V₂ = V

3.Medium

A single-phase 150 kVA, 480/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 150 kVAV₁ = 480 VV₂ = 240 V

I_HV = A

4.Medium

A 50 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 12:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 12:1R_L = 50 Ω

R_1′ = Ω

5.Hard

A single-phase 100 kVA transformer has a core loss of 400 W and a copper loss of 1200 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.95 lagging. Find the total losses P_loss in watts at this load.

S = 100 kVAP_core = 400 WP_cu,fl = 1200 Wx = 0.75pf = 0.95

P_loss = W

6.Hard

A single-phase 50 kVA transformer has a core loss of 200 W. At rated load and a power factor of 0.9 lagging its efficiency is 98.8%. Find the full-load copper loss P_cu,fl in watts.

S = 50 kVAP_core = 200 Wpf = 0.9η = 98.8%

P_cu,fl = W

Answer key

1. V₂ = 2760 V
2. V₂ = 2400 V
3. I_HV = 312.5 A
4. R_1′ = 7200 Ω
5. P_loss = 1075 W
6. P_cu,fl = 346.6 W

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