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​ = 750N2​ = ?2000 V400 V

An ideal transformer must step 2000 V down to 400 V. Its primary winding has 750 turns. How many turns N2 does the secondary winding need?

V1 = 2000 VV2 = 400 VN1 = 750
N2 =
2.Easy
N1​ = 200N2​ = 800690 VV2​ = ?

An ideal transformer has 200 turns on its primary winding and 800 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V2.

N1 = 200N2 = 800V1 = 690 V
V2 = V
3.Medium
RL​ = 6 Ω1011200 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 1200 V applied to its primary winding. A 6 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 10:1V1 = 1200 VRL = 6 Ω
I1 = A
4.Medium
50 ΩN1​N2​800 Ω

An amplifier with an output resistance of 800 Ω drives a 50 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 800 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 800 ΩRL = 50 Ω
a =
5.Hard
pf 0.8150 kVA, 75% load

A single-phase 150 kVA transformer has a core loss of 600 W and a copper loss of 1200 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.8 lagging. Find the total losses Ploss in watts at this load.

S = 150 kVAPcore = 600 WPcu,fl = 1200 Wx = 0.75pf = 0.8
Ploss = W
6.Hard
pf 0.9250 kVA, η = 98.2%

A single-phase 250 kVA transformer has a core loss of 750 W. At rated load and a power factor of 0.9 lagging its efficiency is 98.2%. Find the full-load copper loss Pcu,fl in watts.

S = 250 kVAPcore = 750 Wpf = 0.9η = 98.2%
Pcu,fl = W

Answer key

  1. 1. N2 = 150
  2. 2. V2 = 2760 V
  3. 3. I1 = 2 A
  4. 4. a = 4
  5. 5. Ploss = 1275 W
  6. 6. Pcu,fl = 3374 W

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