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​ = 100N2​ = ?920 V230 V

An ideal transformer must step 920 V down to 230 V. Its primary winding has 100 turns. How many turns N2 does the secondary winding need?

V1 = 920 VV2 = 230 VN1 = 100
N2 =
2.Easy
N1​ = 600N2​ = 150480 VV2​ = ?

An ideal transformer has 600 turns on its primary winding and 150 turns on its secondary winding. The primary is connected to a 480 V AC supply. Find the secondary voltage V2.

N1 = 600N2 = 150V1 = 480 V
V2 = V
3.Medium
6600 V230 VIHV​ILV​ = ?75 kVA

A single-phase 75 kVA, 6600/230 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 75 kVAV1 = 6600 VV2 = 230 V
ILV = A
4.Medium
480 V240 VIHV​ = ?ILV​25 kVA

A single-phase 25 kVA, 480/240 V transformer operates at its rated load. Treat it as ideal. Find the current IHV in the high-voltage winding.

S = 25 kVAV1 = 480 VV2 = 240 V
IHV = A
5.Hard
pf 0.8525 kVA, η = 97%

A single-phase 25 kVA transformer has a core loss of 75 W. At rated load and a power factor of 0.85 lagging its efficiency is 97%. Find the full-load copper loss Pcu,fl in watts.

S = 25 kVAPcore = 75 Wpf = 0.85η = 97%
Pcu,fl = W
6.Hard
150 kVA

A single-phase 150 kVA transformer has a core loss of 600 W and a copper loss of 1800 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 150 kVAPcore = 600 WPcu,fl = 1800 W
Sη,max = kVA

Answer key

  1. 1. N2 = 25
  2. 2. V2 = 120 V
  3. 3. ILV = 326.1 A
  4. 4. IHV = 52.08 A
  5. 5. Pcu,fl = 582.2 W
  6. 6. Sη,max = 86.6 kVA

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