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​ = 150N2​ = 300240 VV2​ = ?

An ideal transformer has 150 turns on its primary winding and 300 turns on its secondary winding. The primary is connected to a 240 V AC supply. Find the secondary voltage V2.

N1 = 150N2 = 300V1 = 240 V
V2 = V
2.Easy
N1​ = 2400N2​ = 609200 VV2​ = ?

An ideal transformer has 2400 turns on its primary winding and 60 turns on its secondary winding. The primary is connected to a 9200 V AC supply. Find the secondary voltage V2.

N1 = 2400N2 = 60V1 = 9200 V
V2 = V
3.Medium
5 ΩN1​N2​45 Ω

An amplifier with an output resistance of 45 Ω drives a 5 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 45 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 45 ΩRL = 5 Ω
a =
4.Medium
5 Ω21

A 5 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 2:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 2:1RL = 5 Ω
R1′ = Ω
5.Hard
pf 0.85500 kVA, 50% load

A single-phase 500 kVA transformer has a core loss of 1500 W and a copper loss of 4500 W at rated load. It supplies 50% 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 = 1500 WPcu,fl = 4500 Wx = 0.5pf = 0.85
Ploss = W
6.Hard
pf 0.825 kVA, η = 98%

A single-phase 25 kVA transformer has a core loss of 150 W. At rated load and a power factor of 0.8 lagging its efficiency is 98%. Find the full-load copper loss Pcu,fl in watts.

S = 25 kVAPcore = 150 Wpf = 0.8η = 98%
Pcu,fl = W

Answer key

  1. 1. V2 = 480 V
  2. 2. V2 = 230 V
  3. 3. a = 3
  4. 4. R1′ = 20 Ω
  5. 5. Ploss = 2625 W
  6. 6. Pcu,fl = 258.2 W

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