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​ = 1200400 VV2​ = ?

An ideal transformer has 150 turns on its primary winding and 1200 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V2.

N1 = 150N2 = 1200V1 = 400 V
V2 = V
2.Easy
N1​ = 60N2​ = 600110 VV2​ = ?

An ideal transformer has 60 turns on its primary winding and 600 turns on its secondary winding. The primary is connected to a 110 V AC supply. Find the secondary voltage V2.

N1 = 60N2 = 600V1 = 110 V
V2 = V
3.Medium
RL​ = 12 Ω1012400 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 2400 V applied to its primary winding. A 12 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 10:1V1 = 2400 VRL = 12 Ω
I1 = A
4.Medium
10 ΩN1​N2​90 Ω

An amplifier with an output resistance of 90 Ω drives a 10 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 90 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 90 ΩRL = 10 Ω
a =
5.Hard
pf 0.8150 kVA, 25% load

A single-phase 150 kVA transformer has a core loss of 450 W and a copper loss of 675 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.8 lagging. Find the total losses Ploss in watts at this load.

S = 150 kVAPcore = 450 WPcu,fl = 675 Wx = 0.25pf = 0.8
Ploss = W
6.Hard
pf 0.8525 kVA, η = 98.2%

A single-phase 25 kVA transformer has a core loss of 150 W. At rated load and a power factor of 0.85 lagging its efficiency is 98.2%. Find the full-load copper loss Pcu,fl in watts.

S = 25 kVAPcore = 150 Wpf = 0.85η = 98.2%
Pcu,fl = W

Answer key

  1. 1. V2 = 3200 V
  2. 2. V2 = 1100 V
  3. 3. I1 = 2 A
  4. 4. a = 3
  5. 5. Ploss = 492.2 W
  6. 6. Pcu,fl = 239.5 W

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