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​ = 320N2​ = 401920 VV2​ = ?

An ideal transformer has 320 turns on its primary winding and 40 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V2.

N1 = 320N2 = 40V1 = 1920 V
V2 = V
2.Easy
N1​ = 100N2​ = ?460 V230 V

An ideal transformer must step 460 V down to 230 V. Its primary winding has 100 turns. How many turns N2 does the secondary winding need?

V1 = 460 VV2 = 230 VN1 = 100
N2 =
3.Medium
4 ΩN1​N2​400 Ω

An amplifier with an output resistance of 400 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 400 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 400 ΩRL = 4 Ω
a =
4.Medium
RL​ = 5 Ω1011200 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 1200 V applied to its primary winding. A 5 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 10:1V1 = 1200 VRL = 5 Ω
I1 = A
5.Hard
50 kVA

A single-phase 50 kVA transformer has a core loss of 300 W and a copper loss of 1200 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 50 kVAPcore = 300 WPcu,fl = 1200 W
Sη,max = kVA
6.Hard
pf 0.975 kVA, 75% load

A single-phase 75 kVA transformer has a core loss of 450 W and a copper loss of 675 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.9 lagging. Find the total losses Ploss in watts at this load.

S = 75 kVAPcore = 450 WPcu,fl = 675 Wx = 0.75pf = 0.9
Ploss = W

Answer key

  1. 1. V2 = 240 V
  2. 2. N2 = 50
  3. 3. a = 10
  4. 4. I1 = 2.4 A
  5. 5. Sη,max = 25 kVA
  6. 6. Ploss = 829.7 W

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