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​ = 200N2​ = ?800 V400 V

An ideal transformer must step 800 V down to 400 V. Its primary winding has 200 turns. How many turns N2 does the secondary winding need?

V1 = 800 VV2 = 400 VN1 = 200
N2 =
2.Easy
N1​ = 2000N2​ = ?6000 V120 V

An ideal transformer must step 6000 V down to 120 V. Its primary winding has 2000 turns. How many turns N2 does the secondary winding need?

V1 = 6000 VV2 = 120 VN1 = 2000
N2 =
3.Medium
50 ΩN1​N2​450 Ω

An amplifier with an output resistance of 450 Ω drives a 50 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 450 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 450 ΩRL = 50 Ω
a =
4.Medium
4800 V240 VIHV​ILV​ = ?25 kVA

A single-phase 25 kVA, 4800/240 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 25 kVAV1 = 4800 VV2 = 240 V
ILV = A
5.Hard
pf 0.825 kVA, 50% load

A single-phase 25 kVA transformer has a core loss of 200 W and a copper loss of 400 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.8 lagging. Find the total losses Ploss in watts at this load.

S = 25 kVAPcore = 200 WPcu,fl = 400 Wx = 0.5pf = 0.8
Ploss = W
6.Hard
pf 0.9550 kVA, η = 98.2%

A single-phase 50 kVA transformer has a core loss of 150 W. At rated load and a power factor of 0.95 lagging its efficiency is 98.2%. Find the full-load copper loss Pcu,fl in watts.

S = 50 kVAPcore = 150 Wpf = 0.95η = 98.2%
Pcu,fl = W

Answer key

  1. 1. N2 = 100
  2. 2. N2 = 40
  3. 3. a = 3
  4. 4. ILV = 104.2 A
  5. 5. Ploss = 300 W
  6. 6. Pcu,fl = 720.7 W

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