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​ = 250N2​ = 2500690 VV2​ = ?

An ideal transformer has 250 turns on its primary winding and 2500 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V2.

N1 = 250N2 = 2500V1 = 690 V
V2 = V
2.Easy
N1​ = 960N2​ = 601920 VV2​ = ?

An ideal transformer has 960 turns on its primary winding and 60 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V2.

N1 = 960N2 = 60V1 = 1920 V
V2 = V
3.Medium
50 ΩN1​N2​3200 Ω

An amplifier with an output resistance of 3200 Ω drives a 50 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 3200 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 3200 ΩRL = 50 Ω
a =
4.Medium
50 Ω81

A 50 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 8:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 8:1RL = 50 Ω
R1′ = Ω
5.Hard
pf 0.9550 kVA, 75% load

A single-phase 50 kVA transformer has a core loss of 150 W and a copper loss of 300 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.95 lagging. Find the total losses Ploss in watts at this load.

S = 50 kVAPcore = 150 WPcu,fl = 300 Wx = 0.75pf = 0.95
Ploss = W
6.Hard
pf 0.8575 kVA, η = 98.8%

A single-phase 75 kVA transformer has a core loss of 450 W. At rated load and a power factor of 0.85 lagging its efficiency is 98.8%. Find the full-load copper loss Pcu,fl in watts.

S = 75 kVAPcore = 450 Wpf = 0.85η = 98.8%
Pcu,fl = W

Answer key

  1. 1. V2 = 6900 V
  2. 2. V2 = 120 V
  3. 3. a = 8
  4. 4. R1′ = 3200 Ω
  5. 5. Ploss = 318.8 W
  6. 6. Pcu,fl = 324.3 W

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