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 800 turns on its primary winding and 200 turns on its secondary winding. The primary is connected to a 480 V AC supply. Find the secondary voltage V₂.

N₁ = 800N₂ = 200V₁ = 480 V

V₂ = V

2.Easy

An ideal transformer has 150 turns on its primary winding and 750 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 150N₂ = 750V₁ = 690 V

V₂ = V

3.Medium

An amplifier with an output resistance of 72 Ω drives an 8 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 = 8 Ω

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 50 kVA transformer has a core loss of 400 W. At rated load and a power factor of 0.85 lagging its efficiency is 96.5%. Find the full-load copper loss P_cu,fl in watts.

S = 50 kVAP_core = 400 Wpf = 0.85η = 96.5%

P_cu,fl = W

6.Hard

A single-phase 200 kVA transformer has a core loss of 800 W and a copper loss of 1600 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 800 WP_cu,fl = 1600 W

S_η,max = kVA

Answer key

1. V₂ = 120 V
2. V₂ = 3450 V
3. a = 3
4. R_1′ = 7200 Ω
5. P_cu,fl = 1141 W
6. S_η,max = 141.4 kVA

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