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​ = 50920 VV2​ = ?

An ideal transformer has 200 turns on its primary winding and 50 turns on its secondary winding. The primary is connected to a 920 V AC supply. Find the secondary voltage V2.

N1 = 200N2 = 50V1 = 920 V
V2 = V
2.Easy
N1​ = 250N2​ = ?600 V120 V

An ideal transformer must step 600 V down to 120 V. Its primary winding has 250 turns. How many turns N2 does the secondary winding need?

V1 = 600 VV2 = 120 VN1 = 250
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
16 Ω61

A 16 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 6:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 6:1RL = 16 Ω
R1′ = Ω
5.Hard
500 kVA

A single-phase 500 kVA transformer has a core loss of 2000 W and a copper loss of 4000 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 500 kVAPcore = 2000 WPcu,fl = 4000 W
Sη,max = kVA
6.Hard
50 kVA

A single-phase 50 kVA transformer has a core loss of 250 W and a copper loss of 500 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 50 kVAPcore = 250 WPcu,fl = 500 W
Sη,max = kVA

Answer key

  1. 1. V2 = 230 V
  2. 2. N2 = 50
  3. 3. a = 3
  4. 4. R1′ = 576 Ω
  5. 5. Sη,max = 353.6 kVA
  6. 6. Sη,max = 35.36 kVA

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