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​ = 500N2​ = 205750 VV2​ = ?

An ideal transformer has 500 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 5750 V AC supply. Find the secondary voltage V2.

N1 = 500N2 = 20V1 = 5750 V
V2 = V
2.Easy
N1​ = 1920N2​ = ?1920 V120 V

An ideal transformer must step 1920 V down to 120 V. Its primary winding has 1920 turns. How many turns N2 does the secondary winding need?

V1 = 1920 VV2 = 120 VN1 = 1920
N2 =
3.Medium
RL​ = 6 Ω51600 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 5:1 has 600 V applied to its primary winding. A 6 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 5:1V1 = 600 VRL = 6 Ω
I1 = A
4.Medium
75 ΩN1​N2​4800 Ω

An amplifier with an output resistance of 4800 Ω drives a 75 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 4800 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 4800 ΩRL = 75 Ω
a =
5.Hard
pf 0.9150 kVA, 50% load

A single-phase 150 kVA transformer has a core loss of 1200 W and a copper loss of 3600 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.9 lagging. Find the total losses Ploss in watts at this load.

S = 150 kVAPcore = 1200 WPcu,fl = 3600 Wx = 0.5pf = 0.9
Ploss = W
6.Hard
pf 0.9150 kVA, η = 98.5%

A single-phase 150 kVA transformer has a core loss of 750 W. At rated load and a power factor of 0.9 lagging its efficiency is 98.5%. Find the full-load copper loss Pcu,fl in watts.

S = 150 kVAPcore = 750 Wpf = 0.9η = 98.5%
Pcu,fl = W

Answer key

  1. 1. V2 = 230 V
  2. 2. N2 = 120
  3. 3. I1 = 4 A
  4. 4. a = 8
  5. 5. Ploss = 2100 W
  6. 6. Pcu,fl = 1306 W

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