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
N1​ = 600N2​ = ?920 V230 V

An ideal transformer must step 920 V down to 230 V. Its primary winding has 600 turns. How many turns N2 does the secondary winding need?

V1 = 920 VV2 = 230 VN1 = 600
N2 =
2.Easy
N1​ = 1200N2​ = ?1920 V240 V

An ideal transformer must step 1920 V down to 240 V. Its primary winding has 1200 turns. How many turns N2 does the secondary winding need?

V1 = 1920 VV2 = 240 VN1 = 1200
N2 =
3.Medium
4 ΩN1​N2​16 Ω

An amplifier with an output resistance of 16 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 16 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 16 ΩRL = 4 Ω
a =
4.Medium
16 ΩN1​N2​1024 Ω

An amplifier with an output resistance of 1024 Ω drives a 16 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 1024 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 1024 ΩRL = 16 Ω
a =
5.Hard
pf 0.950 kVA, 50% load

A single-phase 50 kVA transformer has a core loss of 200 W and a copper loss of 300 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.9 lagging. Find the total losses Ploss in watts at this load.

S = 50 kVAPcore = 200 WPcu,fl = 300 Wx = 0.5pf = 0.9
Ploss = W
6.Hard
pf 0.9150 kVA, η = 96%

A single-phase 150 kVA transformer has a core loss of 750 W. At rated load and a power factor of 0.9 lagging its efficiency is 96%. Find the full-load copper loss Pcu,fl in watts.

S = 150 kVAPcore = 750 Wpf = 0.9η = 96%
Pcu,fl = W

Answer key

  1. 1. N2 = 150
  2. 2. N2 = 150
  3. 3. a = 2
  4. 4. a = 8
  5. 5. Ploss = 275 W
  6. 6. Pcu,fl = 4875 W

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