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​ = 600N2​ = 602400 VV2​ = ?

An ideal transformer has 600 turns on its primary winding and 60 turns on its secondary winding. The primary is connected to a 2400 V AC supply. Find the secondary voltage V2.

N1 = 600N2 = 60V1 = 2400 V
V2 = V
2.Easy
N1​ = 400N2​ = ?1200 V240 V

An ideal transformer must step 1200 V down to 240 V. Its primary winding has 400 turns. How many turns N2 does the secondary winding need?

V1 = 1200 VV2 = 240 VN1 = 400
N2 =
3.Medium
2 Ω51

A 2 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 5:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 5:1RL = 2 Ω
R1′ = Ω
4.Medium
2400 V240 VIHV​ILV​ = ?25 kVA

A single-phase 25 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 25 kVAV1 = 2400 VV2 = 240 V
ILV = A
5.Hard
pf 0.8575 kVA, η = 98.5%

A single-phase 75 kVA transformer has a core loss of 600 W. At rated load and a power factor of 0.85 lagging its efficiency is 98.5%. Find the full-load copper loss Pcu,fl in watts.

S = 75 kVAPcore = 600 Wpf = 0.85η = 98.5%
Pcu,fl = W
6.Hard
25 kVA

A single-phase 25 kVA transformer has a core loss of 125 W and a copper loss of 375 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 25 kVAPcore = 125 WPcu,fl = 375 W
Sη,max = kVA

Answer key

  1. 1. V2 = 240 V
  2. 2. N2 = 80
  3. 3. R1′ = 50 Ω
  4. 4. ILV = 104.2 A
  5. 5. Pcu,fl = 370.8 W
  6. 6. Sη,max = 14.43 kVA

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