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 1280 turns on its primary winding and 80 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V₂.

N₁ = 1280N₂ = 80V₁ = 1920 V

V₂ = V

2.Easy

An ideal transformer has 40 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 460 V AC supply. Find the secondary voltage V₂.

N₁ = 40N₂ = 20V₁ = 460 V

V₂ = V

3.Medium

A single-phase 150 kVA, 10000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 150 kVAV₁ = 10000 VV₂ = 400 V

I_HV = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 480 V applied to its primary winding. A 15 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 4:1V₁ = 480 VR_L = 15 Ω

I₁ = A

5.Hard

A single-phase 200 kVA transformer has a core loss of 1600 W. At rated load and a power factor of 0.9 lagging its efficiency is 97.5%. Find the full-load copper loss P_cu,fl in watts.

S = 200 kVAP_core = 1600 Wpf = 0.9η = 97.5%

P_cu,fl = W

6.Hard

A single-phase 150 kVA transformer has a core loss of 1200 W and a copper loss of 3000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 150 kVAP_core = 1200 WP_cu,fl = 3000 W

S_η,max = kVA

Answer key

1. V₂ = 120 V
2. V₂ = 230 V
3. I_HV = 15 A
4. I₁ = 2 A
5. P_cu,fl = 3015 W
6. S_η,max = 94.87 kVA

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