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​ = 500N2​ = ?600 V120 V

An ideal transformer must step 600 V down to 120 V. Its primary winding has 500 turns. How many turns N2 does the secondary winding need?

V1 = 600 VV2 = 120 VN1 = 500
N2 =
2.Easy
N1​ = 3000N2​ = 12010000 VV2​ = ?

An ideal transformer has 3000 turns on its primary winding and 120 turns on its secondary winding. The primary is connected to a 10000 V AC supply. Find the secondary voltage V2.

N1 = 3000N2 = 120V1 = 10000 V
V2 = V
3.Medium
7200 V240 VIHV​ILV​ = ?100 kVA

A single-phase 100 kVA, 7200/240 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 100 kVAV1 = 7200 VV2 = 240 V
ILV = A
4.Medium
5 Ω41

A 5 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 = 5 Ω
R1′ = Ω
5.Hard
50 kVA

A single-phase 50 kVA transformer has a core loss of 400 W and a copper loss of 1600 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 50 kVAPcore = 400 WPcu,fl = 1600 W
Sη,max = kVA
6.Hard
pf 0.9500 kVA, η = 96.5%

A single-phase 500 kVA transformer has a core loss of 4000 W. At rated load and a power factor of 0.9 lagging its efficiency is 96.5%. Find the full-load copper loss Pcu,fl in watts.

S = 500 kVAPcore = 4000 Wpf = 0.9η = 96.5%
Pcu,fl = W

Answer key

  1. 1. N2 = 100
  2. 2. V2 = 400 V
  3. 3. ILV = 416.7 A
  4. 4. R1′ = 80 Ω
  5. 5. Sη,max = 25 kVA
  6. 6. Pcu,fl = 12321 W

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