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 1000 turns on its primary winding and 40 turns on its secondary winding. The primary is connected to a 10000 V AC supply. Find the secondary voltage V₂.

N₁ = 1000N₂ = 40V₁ = 10000 V

V₂ = V

2.Easy

An ideal transformer has 250 turns on its primary winding and 500 turns on its secondary winding. The primary is connected to a 240 V AC supply. Find the secondary voltage V₂.

N₁ = 250N₂ = 500V₁ = 240 V

V₂ = V

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 240 V applied to its primary winding. A 60 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 240 VR_L = 60 Ω

I₁ = A

4.Medium

An amplifier with an output resistance of 128 Ω drives a 2 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 128 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 128 ΩR_L = 2 Ω

a =

5.Hard

A single-phase 100 kVA transformer has a core loss of 400 W and a copper loss of 1200 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 100 kVAP_core = 400 WP_cu,fl = 1200 W

S_η,max = kVA

6.Hard

A single-phase 50 kVA transformer has a core loss of 200 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 = 200 Wpf = 0.85η = 96.5%

P_cu,fl = W

Answer key

1. V₂ = 400 V
2. V₂ = 480 V
3. I₁ = 1 A
4. a = 8
5. S_η,max = 57.74 kVA
6. P_cu,fl = 1341 W

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