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​ = 150N2​ = 7500110 VV2​ = ?

An ideal transformer has 150 turns on its primary winding and 7500 turns on its secondary winding. The primary is connected to a 110 V AC supply. Find the secondary voltage V2.

N1 = 150N2 = 7500V1 = 110 V
V2 = V
2.Easy
N1​ = 240N2​ = 60920 VV2​ = ?

An ideal transformer has 240 turns on its primary winding and 60 turns on its secondary winding. The primary is connected to a 920 V AC supply. Find the secondary voltage V2.

N1 = 240N2 = 60V1 = 920 V
V2 = V
3.Medium
RL​ = 12 Ω41480 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 480 V applied to its primary winding. A 12 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 4:1V1 = 480 VRL = 12 Ω
I1 = A
4.Medium
RL​ = 6 Ω21460 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 460 V applied to its primary winding. A 6 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 2:1V1 = 460 VRL = 6 Ω
I1 = A
5.Hard
pf 0.9550 kVA, 25% load

A single-phase 50 kVA transformer has a core loss of 250 W and a copper loss of 750 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.95 lagging. Find the total losses Ploss in watts at this load.

S = 50 kVAPcore = 250 WPcu,fl = 750 Wx = 0.25pf = 0.95
Ploss = W
6.Hard
pf 0.9525 kVA, η = 99%

A single-phase 25 kVA transformer has a core loss of 100 W. At rated load and a power factor of 0.95 lagging its efficiency is 99%. Find the full-load copper loss Pcu,fl in watts.

S = 25 kVAPcore = 100 Wpf = 0.95η = 99%
Pcu,fl = W

Answer key

  1. 1. V2 = 5500 V
  2. 2. V2 = 230 V
  3. 3. I1 = 2.5 A
  4. 4. I1 = 19.17 A
  5. 5. Ploss = 296.9 W
  6. 6. Pcu,fl = 139.9 W

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