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​ = 160N2​ = ?1920 V240 V

An ideal transformer must step 1920 V down to 240 V. Its primary winding has 160 turns. How many turns N2 does the secondary winding need?

V1 = 1920 VV2 = 240 VN1 = 160
N2 =
2.Easy
N1​ = 250N2​ = 2500690 VV2​ = ?

An ideal transformer has 250 turns on its primary winding and 2500 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V2.

N1 = 250N2 = 2500V1 = 690 V
V2 = V
3.Medium
11000 V400 VIHV​ILV​ = ?100 kVA

A single-phase 100 kVA, 11000/400 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 100 kVAV1 = 11000 VV2 = 400 V
ILV = A
4.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 IHV in the high-voltage winding.

S = 100 kVAV1 = 7200 VV2 = 240 V
IHV = A
5.Hard
pf 0.975 kVA, 75% load

A single-phase 75 kVA transformer has a core loss of 225 W and a copper loss of 450 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.9 lagging. Find the total losses Ploss in watts at this load.

S = 75 kVAPcore = 225 WPcu,fl = 450 Wx = 0.75pf = 0.9
Ploss = W
6.Hard
pf 0.85200 kVA, η = 98.5%

A single-phase 200 kVA transformer has a core loss of 1200 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 = 200 kVAPcore = 1200 Wpf = 0.85η = 98.5%
Pcu,fl = W

Answer key

  1. 1. N2 = 20
  2. 2. V2 = 6900 V
  3. 3. ILV = 250 A
  4. 4. IHV = 13.89 A
  5. 5. Ploss = 478.1 W
  6. 6. Pcu,fl = 1389 W

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