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 200 turns on its primary winding and 1000 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 200N₂ = 1000V₁ = 690 V

V₂ = V

2.Easy

An ideal transformer has 320 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 3840 V AC supply. Find the secondary voltage V₂.

N₁ = 320N₂ = 20V₁ = 3840 V

V₂ = V

3.Medium

An amplifier with an output resistance of 720 Ω drives a 5 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 720 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 720 ΩR_L = 5 Ω

a =

4.Medium

A 75 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 = 75 Ω

R_1′ = Ω

5.Hard

A single-phase 75 kVA transformer has a core loss of 450 W and a copper loss of 675 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 450 WP_cu,fl = 675 W

S_η,max = kVA

6.Hard

A single-phase 75 kVA transformer has a core loss of 600 W and a copper loss of 1200 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 600 WP_cu,fl = 1200 W

S_η,max = kVA

Answer key

1. V₂ = 3450 V
2. V₂ = 240 V
3. a = 12
4. R_1′ = 1875 Ω
5. S_η,max = 61.24 kVA
6. S_η,max = 53.03 kVA

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