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 4000 turns on its primary winding and 200 turns on its secondary winding. The primary is connected to a 4600 V AC supply. Find the secondary voltage V₂.

N₁ = 4000N₂ = 200V₁ = 4600 V

V₂ = V

2.Easy

An ideal transformer must step 10000 V down to 400 V. Its primary winding has 2000 turns. How many turns N₂ does the secondary winding need?

V₁ = 10000 VV₂ = 400 VN₁ = 2000

N₂ =

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 5:1 has 1150 V applied to its primary winding. An 8 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 5:1V₁ = 1150 VR_L = 8 Ω

I₁ = A

4.Medium

An amplifier with an output resistance of 50 Ω drives a 2 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 50 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 50 ΩR_L = 2 Ω

a =

5.Hard

A single-phase 150 kVA transformer has a core loss of 600 W. At rated load and a power factor of 0.8 lagging its efficiency is 97%. Find the full-load copper loss P_cu,fl in watts.

S = 150 kVAP_core = 600 Wpf = 0.8η = 97%

P_cu,fl = W

6.Hard

A single-phase 100 kVA transformer has a core loss of 300 W and a copper loss of 750 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 100 kVAP_core = 300 WP_cu,fl = 750 W

S_η,max = kVA

Answer key

1. V₂ = 230 V
2. N₂ = 80
3. I₁ = 5.75 A
4. a = 5
5. P_cu,fl = 3111 W
6. S_η,max = 63.25 kVA

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