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 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

2.Easy

An ideal transformer has 500 turns on its primary winding and 25 turns on its secondary winding. The primary is connected to a 4800 V AC supply. Find the secondary voltage V₂.

N₁ = 500N₂ = 25V₁ = 4800 V

V₂ = V

3.Medium

An amplifier with an output resistance of 450 Ω drives a 50 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 450 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 450 ΩR_L = 50 Ω

a =

4.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

5.Hard

A single-phase 500 kVA transformer has a core loss of 1500 W. At rated load and a power factor of 0.95 lagging its efficiency is 99%. Find the full-load copper loss P_cu,fl in watts.

S = 500 kVAP_core = 1500 Wpf = 0.95η = 99%

P_cu,fl = W

6.Hard

A single-phase 100 kVA transformer has a core loss of 500 W and a copper loss of 1250 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 100 kVAP_core = 500 WP_cu,fl = 1250 W

S_η,max = kVA

Answer key

1. V₂ = 230 V
2. V₂ = 240 V
3. a = 3
4. I₁ = 1 A
5. P_cu,fl = 3298 W
6. S_η,max = 63.25 kVA

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