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 160 turns on its primary winding and 40 turns on its secondary winding. The primary is connected to a 480 V AC supply. Find the secondary voltage V₂.

N₁ = 160N₂ = 40V₁ = 480 V

V₂ = V

2.Easy

An ideal transformer has 80 turns on its primary winding and 1600 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 1600V₁ = 690 V

V₂ = V

3.Medium

A single-phase 15 kVA, 11000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 15 kVAV₁ = 11000 VV₂ = 400 V

I_HV = A

4.Medium

An amplifier with an output resistance of 256 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 256 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 256 ΩR_L = 4 Ω

a =

5.Hard

A single-phase 25 kVA transformer has a core loss of 150 W. At rated load and a power factor of 0.85 lagging its efficiency is 98.5%. Find the full-load copper loss P_cu,fl in watts.

S = 25 kVAP_core = 150 Wpf = 0.85η = 98.5%

P_cu,fl = W

6.Hard

A single-phase 100 kVA transformer has a core loss of 800 W. At rated load and a power factor of 0.8 lagging its efficiency is 98%. Find the full-load copper loss P_cu,fl in watts.

S = 100 kVAP_core = 800 Wpf = 0.8η = 98%

P_cu,fl = W

Answer key

1. V₂ = 120 V
2. V₂ = 13800 V
3. I_HV = 1.364 A
4. a = 8
5. P_cu,fl = 173.6 W
6. P_cu,fl = 832.7 W

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