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 800 turns on its primary winding and 40 turns on its secondary winding. The primary is connected to an 8000 V AC supply. Find the secondary voltage V₂.

N₁ = 800N₂ = 40V₁ = 8000 V

V₂ = V

3.Medium

A 2 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 5:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 5:1R_L = 2 Ω

R_1′ = Ω

4.Medium

An amplifier with an output resistance of 72 Ω drives a 2 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 72 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 72 ΩR_L = 2 Ω

a =

5.Hard

A single-phase 200 kVA transformer has a core loss of 1600 W and a copper loss of 4800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 1600 WP_cu,fl = 4800 W

S_η,max = kVA

6.Hard

A single-phase 75 kVA transformer has a core loss of 375 W. At rated load and a power factor of 0.9 lagging its efficiency is 96.5%. Find the full-load copper loss P_cu,fl in watts.

S = 75 kVAP_core = 375 Wpf = 0.9η = 96.5%

P_cu,fl = W

Answer key

1. V₂ = 120 V
2. V₂ = 400 V
3. R_1′ = 50 Ω
4. a = 6
5. S_η,max = 115.5 kVA
6. P_cu,fl = 2073 W

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