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​ = 625N2​ = 256000 VV2​ = ?

An ideal transformer has 625 turns on its primary winding and 25 turns on its secondary winding. The primary is connected to a 6000 V AC supply. Find the secondary voltage V2.

N1 = 625N2 = 25V1 = 6000 V
V2 = V
2.Easy
N1​ = 3000N2​ = 12010000 VV2​ = ?

An ideal transformer has 3000 turns on its primary winding and 120 turns on its secondary winding. The primary is connected to a 10000 V AC supply. Find the secondary voltage V2.

N1 = 3000N2 = 120V1 = 10000 V
V2 = V
3.Medium
75 ΩN1​N2​10800 Ω

An amplifier with an output resistance of 10800 Ω drives a 75 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 10800 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 10800 ΩRL = 75 Ω
a =
4.Medium
16 ΩN1​N2​1600 Ω

An amplifier with an output resistance of 1600 Ω drives a 16 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 1600 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 1600 ΩRL = 16 Ω
a =
5.Hard
pf 0.9150 kVA, η = 98.5%

A single-phase 150 kVA transformer has a core loss of 600 W. At rated load and a power factor of 0.9 lagging its efficiency is 98.5%. Find the full-load copper loss Pcu,fl in watts.

S = 150 kVAPcore = 600 Wpf = 0.9η = 98.5%
Pcu,fl = W
6.Hard
250 kVA

A single-phase 250 kVA transformer has a core loss of 750 W and a copper loss of 1875 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 250 kVAPcore = 750 WPcu,fl = 1875 W
Sη,max = kVA

Answer key

  1. 1. V2 = 240 V
  2. 2. V2 = 400 V
  3. 3. a = 12
  4. 4. a = 10
  5. 5. Pcu,fl = 1456 W
  6. 6. Sη,max = 158.1 kVA

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