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​ = 240N2​ = ?460 V230 V

An ideal transformer must step 460 V down to 230 V. Its primary winding has 240 turns. How many turns N2 does the secondary winding need?

V1 = 460 VV2 = 230 VN1 = 240
N2 =
2.Easy
N1​ = 800N2​ = 501920 VV2​ = ?

An ideal transformer has 800 turns on its primary winding and 50 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V2.

N1 = 800N2 = 50V1 = 1920 V
V2 = V
3.Medium
2400 V240 VIHV​ILV​ = ?250 kVA

A single-phase 250 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 250 kVAV1 = 2400 VV2 = 240 V
ILV = A
4.Medium
RL​ = 15 Ω1012400 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 2400 V applied to its primary winding. A 15 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 10:1V1 = 2400 VRL = 15 Ω
I1 = A
5.Hard
pf 0.825 kVA, η = 96%

A single-phase 25 kVA transformer has a core loss of 125 W. At rated load and a power factor of 0.8 lagging its efficiency is 96%. Find the full-load copper loss Pcu,fl in watts.

S = 25 kVAPcore = 125 Wpf = 0.8η = 96%
Pcu,fl = W
6.Hard
pf 0.9100 kVA, η = 98.5%

A single-phase 100 kVA transformer has a core loss of 400 W. At rated load and a power factor of 0.9 lagging its efficiency is 98.5%. Find the full-load copper loss Pcu,fl in watts.

S = 100 kVAPcore = 400 Wpf = 0.9η = 98.5%
Pcu,fl = W

Answer key

  1. 1. N2 = 120
  2. 2. V2 = 120 V
  3. 3. ILV = 1042 A
  4. 4. I1 = 1.6 A
  5. 5. Pcu,fl = 708.3 W
  6. 6. Pcu,fl = 970.6 W

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