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​ = 400N2​ = ?240 V120 V

An ideal transformer must step 240 V down to 120 V. Its primary winding has 400 turns. How many turns N2 does the secondary winding need?

V1 = 240 VV2 = 120 VN1 = 400
N2 =
2.Easy
N1​ = 60N2​ = 1500110 VV2​ = ?

An ideal transformer has 60 turns on its primary winding and 1500 turns on its secondary winding. The primary is connected to a 110 V AC supply. Find the secondary voltage V2.

N1 = 60N2 = 1500V1 = 110 V
V2 = V
3.Medium
RL​ = 40 Ω41920 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 920 V applied to its primary winding. A 40 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 4:1V1 = 920 VRL = 40 Ω
I1 = A
4.Medium
8 Ω41

An 8 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 4:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 4:1RL = 8 Ω
R1′ = Ω
5.Hard
25 kVA

A single-phase 25 kVA transformer has a core loss of 150 W and a copper loss of 300 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 25 kVAPcore = 150 WPcu,fl = 300 W
Sη,max = kVA
6.Hard
50 kVA

A single-phase 50 kVA transformer has a core loss of 150 W and a copper loss of 225 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 50 kVAPcore = 150 WPcu,fl = 225 W
Sη,max = kVA

Answer key

  1. 1. N2 = 200
  2. 2. V2 = 2750 V
  3. 3. I1 = 1.438 A
  4. 4. R1′ = 128 Ω
  5. 5. Sη,max = 17.68 kVA
  6. 6. Sη,max = 40.82 kVA

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