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​ = 120N2​ = 6000400 VV2​ = ?

An ideal transformer has 120 turns on its primary winding and 6000 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V2.

N1 = 120N2 = 6000V1 = 400 V
V2 = V
2.Easy
N1​ = 600N2​ = 1201200 VV2​ = ?

An ideal transformer has 600 turns on its primary winding and 120 turns on its secondary winding. The primary is connected to a 1200 V AC supply. Find the secondary voltage V2.

N1 = 600N2 = 120V1 = 1200 V
V2 = V
3.Medium
5 ΩN1​N2​20 Ω

An amplifier with an output resistance of 20 Ω drives a 5 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 20 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 20 ΩRL = 5 Ω
a =
4.Medium
16 ΩN1​N2​576 Ω

An amplifier with an output resistance of 576 Ω drives a 16 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 576 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 576 ΩRL = 16 Ω
a =
5.Hard
pf 0.85250 kVA, 25% load

A single-phase 250 kVA transformer has a core loss of 1000 W and a copper loss of 2500 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.85 lagging. Find the total losses Ploss in watts at this load.

S = 250 kVAPcore = 1000 WPcu,fl = 2500 Wx = 0.25pf = 0.85
Ploss = W
6.Hard
pf 0.8575 kVA, η = 97.5%

A single-phase 75 kVA transformer has a core loss of 300 W. At rated load and a power factor of 0.85 lagging its efficiency is 97.5%. Find the full-load copper loss Pcu,fl in watts.

S = 75 kVAPcore = 300 Wpf = 0.85η = 97.5%
Pcu,fl = W

Answer key

  1. 1. V2 = 20000 V
  2. 2. V2 = 240 V
  3. 3. a = 2
  4. 4. a = 6
  5. 5. Ploss = 1156 W
  6. 6. Pcu,fl = 1335 W

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