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 640 turns on its primary winding and 40 turns on its secondary winding. The primary is connected to a 3840 V AC supply. Find the secondary voltage V₂.

N₁ = 640N₂ = 40V₁ = 3840 V

V₂ = V

2.Easy

An ideal transformer must step 9200 V down to 230 V. Its primary winding has 8000 turns. How many turns N₂ does the secondary winding need?

V₁ = 9200 VV₂ = 230 VN₁ = 8000

N₂ =

3.Medium

An amplifier with an output resistance of 64 Ω drives a 16 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 64 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 64 ΩR_L = 16 Ω

a =

4.Medium

A single-phase 100 kVA, 7200/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 100 kVAV₁ = 7200 VV₂ = 240 V

I_LV = A

5.Hard

A single-phase 500 kVA transformer has a core loss of 2000 W and a copper loss of 4000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 2000 WP_cu,fl = 4000 W

S_η,max = kVA

6.Hard

A single-phase 150 kVA transformer has a core loss of 1200 W. At rated load and a power factor of 0.9 lagging its efficiency is 97.5%. Find the full-load copper loss P_cu,fl in watts.

S = 150 kVAP_core = 1200 Wpf = 0.9η = 97.5%

P_cu,fl = W

Answer key

1. V₂ = 240 V
2. N₂ = 200
3. a = 2
4. I_LV = 416.7 A
5. S_η,max = 353.6 kVA
6. P_cu,fl = 2262 W

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