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​ = 1600N2​ = 1003840 VV2​ = ?

An ideal transformer has 1600 turns on its primary winding and 100 turns on its secondary winding. The primary is connected to a 3840 V AC supply. Find the secondary voltage V2.

N1 = 1600N2 = 100V1 = 3840 V
V2 = V
2.Easy
N1​ = 1000N2​ = 259200 VV2​ = ?

An ideal transformer has 1000 turns on its primary winding and 25 turns on its secondary winding. The primary is connected to a 9200 V AC supply. Find the secondary voltage V2.

N1 = 1000N2 = 25V1 = 9200 V
V2 = V
3.Medium
10 Ω101

A 10 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 10:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 10:1RL = 10 Ω
R1′ = Ω
4.Medium
2 ΩN1​N2​8 Ω

An amplifier with an output resistance of 8 Ω drives a 2 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 8 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 8 ΩRL = 2 Ω
a =
5.Hard
pf 0.85500 kVA, 25% load

A single-phase 500 kVA transformer has a core loss of 3000 W and a copper loss of 9000 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 = 500 kVAPcore = 3000 WPcu,fl = 9000 Wx = 0.25pf = 0.85
Ploss = W
6.Hard
pf 0.825 kVA, η = 97.5%

A single-phase 25 kVA transformer has a core loss of 100 W. At rated load and a power factor of 0.8 lagging its efficiency is 97.5%. Find the full-load copper loss Pcu,fl in watts.

S = 25 kVAPcore = 100 Wpf = 0.8η = 97.5%
Pcu,fl = W

Answer key

  1. 1. V2 = 240 V
  2. 2. V2 = 230 V
  3. 3. R1′ = 1000 Ω
  4. 4. a = 2
  5. 5. Ploss = 3563 W
  6. 6. Pcu,fl = 412.8 W

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