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​ = 1600N2​ = ?9600 V240 V

An ideal transformer must step 9600 V down to 240 V. Its primary winding has 1600 turns. How many turns N2 does the secondary winding need?

V1 = 9600 VV2 = 240 VN1 = 1600
N2 =
2.Easy
N1​ = 40N2​ = ?480 V240 V

An ideal transformer must step 480 V down to 240 V. Its primary winding has 40 turns. How many turns N2 does the secondary winding need?

V1 = 480 VV2 = 240 VN1 = 40
N2 =
3.Medium
RL​ = 5 Ω41960 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 960 V applied to its primary winding. A 5 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 4:1V1 = 960 VRL = 5 Ω
I1 = A
4.Medium
2400 V240 VIHV​ = ?ILV​100 kVA

A single-phase 100 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current IHV in the high-voltage winding.

S = 100 kVAV1 = 2400 VV2 = 240 V
IHV = A
5.Hard
pf 0.8575 kVA, η = 98%

A single-phase 75 kVA transformer has a core loss of 300 W. At rated load and a power factor of 0.85 lagging its efficiency is 98%. Find the full-load copper loss Pcu,fl in watts.

S = 75 kVAPcore = 300 Wpf = 0.85η = 98%
Pcu,fl = W
6.Hard
500 kVA

A single-phase 500 kVA transformer has a core loss of 2500 W and a copper loss of 10000 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 500 kVAPcore = 2500 WPcu,fl = 10000 W
Sη,max = kVA

Answer key

  1. 1. N2 = 40
  2. 2. N2 = 20
  3. 3. I1 = 12 A
  4. 4. IHV = 41.67 A
  5. 5. Pcu,fl = 1001 W
  6. 6. Sη,max = 250 kVA

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