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 60 turns on its primary winding and 240 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 60N₂ = 240V₁ = 690 V

V₂ = V

2.Easy

An ideal transformer must step 920 V down to 230 V. Its primary winding has 200 turns. How many turns N₂ does the secondary winding need?

V₁ = 920 VV₂ = 230 VN₁ = 200

N₂ =

3.Medium

An amplifier with an output resistance of 1000 Ω drives a 10 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 1000 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 1000 ΩR_L = 10 Ω

a =

4.Medium

A single-phase 150 kVA, 10000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 150 kVAV₁ = 10000 VV₂ = 400 V

I_LV = A

5.Hard

A single-phase 500 kVA transformer has a core loss of 3000 W. At rated load and a power factor of 0.9 lagging its efficiency is 99%. Find the full-load copper loss P_cu,fl in watts.

S = 500 kVAP_core = 3000 Wpf = 0.9η = 99%

P_cu,fl = W

6.Hard

A single-phase 50 kVA transformer has a core loss of 250 W and a copper loss of 500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 50 kVAP_core = 250 WP_cu,fl = 500 W

S_η,max = kVA

Answer key

1. V₂ = 2760 V
2. N₂ = 50
3. a = 10
4. I_LV = 375 A
5. P_cu,fl = 1545 W
6. S_η,max = 35.36 kVA

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