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​ = 120N2​ = ?460 V230 V

An ideal transformer must step 460 V down to 230 V. Its primary winding has 120 turns. How many turns N2 does the secondary winding need?

V1 = 460 VV2 = 230 VN1 = 120
N2 =
2.Easy
N1​ = 1500N2​ = 1504000 VV2​ = ?

An ideal transformer has 1500 turns on its primary winding and 150 turns on its secondary winding. The primary is connected to a 4000 V AC supply. Find the secondary voltage V2.

N1 = 1500N2 = 150V1 = 4000 V
V2 = V
3.Medium
4 ΩN1​N2​36 Ω

An amplifier with an output resistance of 36 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 36 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 36 ΩRL = 4 Ω
a =
4.Medium
2 ΩN1​N2​32 Ω

An amplifier with an output resistance of 32 Ω drives a 2 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 32 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 32 ΩRL = 2 Ω
a =
5.Hard
pf 0.85500 kVA, 25% load

A single-phase 500 kVA transformer has a core loss of 1500 W and a copper loss of 3000 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 = 1500 WPcu,fl = 3000 Wx = 0.25pf = 0.85
Ploss = W
6.Hard
pf 0.8100 kVA, 75% load

A single-phase 100 kVA transformer has a core loss of 500 W and a copper loss of 750 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.8 lagging. Find the total losses Ploss in watts at this load.

S = 100 kVAPcore = 500 WPcu,fl = 750 Wx = 0.75pf = 0.8
Ploss = W

Answer key

  1. 1. N2 = 60
  2. 2. V2 = 400 V
  3. 3. a = 3
  4. 4. a = 4
  5. 5. Ploss = 1688 W
  6. 6. Ploss = 921.9 W

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