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​ = 125N2​ = ?2000 V400 V

An ideal transformer must step 2000 V down to 400 V. Its primary winding has 125 turns. How many turns N2 does the secondary winding need?

V1 = 2000 VV2 = 400 VN1 = 125
N2 =
2.Easy
N1​ = 160N2​ = 201920 VV2​ = ?

An ideal transformer has 160 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V2.

N1 = 160N2 = 20V1 = 1920 V
V2 = V
3.Medium
2 Ω31

A 2 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 3:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 3:1RL = 2 Ω
R1′ = Ω
4.Medium
7200 V240 VIHV​ = ?ILV​15 kVA

A single-phase 15 kVA, 7200/240 V transformer operates at its rated load. Treat it as ideal. Find the current IHV in the high-voltage winding.

S = 15 kVAV1 = 7200 VV2 = 240 V
IHV = A
5.Hard
pf 0.95500 kVA, η = 97.5%

A single-phase 500 kVA transformer has a core loss of 4000 W. At rated load and a power factor of 0.95 lagging its efficiency is 97.5%. Find the full-load copper loss Pcu,fl in watts.

S = 500 kVAPcore = 4000 Wpf = 0.95η = 97.5%
Pcu,fl = W
6.Hard
25 kVA

A single-phase 25 kVA transformer has a core loss of 100 W and a copper loss of 250 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 25 kVAPcore = 100 WPcu,fl = 250 W
Sη,max = kVA

Answer key

  1. 1. N2 = 25
  2. 2. V2 = 240 V
  3. 3. R1′ = 18 Ω
  4. 4. IHV = 2.083 A
  5. 5. Pcu,fl = 8179 W
  6. 6. Sη,max = 15.81 kVA

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