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​ = 60N2​ = 120240 VV2​ = ?

An ideal transformer has 60 turns on its primary winding and 120 turns on its secondary winding. The primary is connected to a 240 V AC supply. Find the secondary voltage V2.

N1 = 60N2 = 120V1 = 240 V
V2 = V
2.Easy
N1​ = 6000N2​ = ?11500 V230 V

An ideal transformer must step 11500 V down to 230 V. Its primary winding has 6000 turns. How many turns N2 does the secondary winding need?

V1 = 11500 VV2 = 230 VN1 = 6000
N2 =
3.Medium
RL​ = 48 Ω1012300 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 2300 V applied to its primary winding. A 48 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 10:1V1 = 2300 VRL = 48 Ω
I1 = A
4.Medium
2 ΩN1​N2​128 Ω

An amplifier with an output resistance of 128 Ω drives a 2 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 128 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 128 ΩRL = 2 Ω
a =
5.Hard
pf 0.85250 kVA, 25% load

A single-phase 250 kVA transformer has a core loss of 1000 W and a copper loss of 2000 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.85 lagging. Find the total losses Ploss in watts at this load.

S = 250 kVAPcore = 1000 WPcu,fl = 2000 Wx = 0.25pf = 0.85
Ploss = W
6.Hard
pf 0.8200 kVA, η = 97%

A single-phase 200 kVA transformer has a core loss of 1000 W. At rated load and a power factor of 0.8 lagging its efficiency is 97%. Find the full-load copper loss Pcu,fl in watts.

S = 200 kVAPcore = 1000 Wpf = 0.8η = 97%
Pcu,fl = W

Answer key

  1. 1. V2 = 480 V
  2. 2. N2 = 120
  3. 3. I1 = 0.4792 A
  4. 4. a = 8
  5. 5. Ploss = 1125 W
  6. 6. Pcu,fl = 3948 W

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