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 400 turns on its primary winding and 50 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V₂.

N₁ = 400N₂ = 50V₁ = 1920 V

V₂ = V

2.Easy

An ideal transformer has 240 turns on its primary winding and 60 turns on its secondary winding. The primary is connected to a 920 V AC supply. Find the secondary voltage V₂.

N₁ = 240N₂ = 60V₁ = 920 V

V₂ = V

3.Medium

An amplifier with an output resistance of 36 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 36 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 36 ΩR_L = 4 Ω

a =

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 20:1 has 4600 V applied to its primary winding. A 6 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 20:1V₁ = 4600 VR_L = 6 Ω

I₁ = A

5.Hard

A single-phase 100 kVA transformer has a core loss of 400 W. At rated load and a power factor of 0.8 lagging its efficiency is 99%. Find the full-load copper loss P_cu,fl in watts.

S = 100 kVAP_core = 400 Wpf = 0.8η = 99%

P_cu,fl = W

6.Hard

A single-phase 50 kVA transformer has a core loss of 400 W and a copper loss of 800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 50 kVAP_core = 400 WP_cu,fl = 800 W

S_η,max = kVA

Answer key

1. V₂ = 240 V
2. V₂ = 230 V
3. a = 3
4. I₁ = 1.917 A
5. P_cu,fl = 408.1 W
6. S_η,max = 35.36 kVA

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