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​ = 200N2​ = ?960 V240 V

An ideal transformer must step 960 V down to 240 V. Its primary winding has 200 turns. How many turns N2 does the secondary winding need?

V1 = 960 VV2 = 240 VN1 = 200
N2 =
2.Easy
N1​ = 200N2​ = ?2400 V240 V

An ideal transformer must step 2400 V down to 240 V. Its primary winding has 200 turns. How many turns N2 does the secondary winding need?

V1 = 2400 VV2 = 240 VN1 = 200
N2 =
3.Medium
480 V240 VIHV​ = ?ILV​10 kVA

A single-phase 10 kVA, 480/240 V transformer operates at its rated load. Treat it as ideal. Find the current IHV in the high-voltage winding.

S = 10 kVAV1 = 480 VV2 = 240 V
IHV = A
4.Medium
RL​ = 30 Ω21480 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 480 V applied to its primary winding. A 30 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 2:1V1 = 480 VRL = 30 Ω
I1 = A
5.Hard
pf 0.9550 kVA, η = 96%

A single-phase 50 kVA transformer has a core loss of 400 W. At rated load and a power factor of 0.95 lagging its efficiency is 96%. Find the full-load copper loss Pcu,fl in watts.

S = 50 kVAPcore = 400 Wpf = 0.95η = 96%
Pcu,fl = W
6.Hard
500 kVA

A single-phase 500 kVA transformer has a core loss of 1500 W and a copper loss of 3750 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 500 kVAPcore = 1500 WPcu,fl = 3750 W
Sη,max = kVA

Answer key

  1. 1. N2 = 50
  2. 2. N2 = 20
  3. 3. IHV = 20.83 A
  4. 4. I1 = 4 A
  5. 5. Pcu,fl = 1579 W
  6. 6. Sη,max = 316.2 kVA

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