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​ = 480690 VV2​ = ?

An ideal transformer has 60 turns on its primary winding and 480 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V2.

N1 = 60N2 = 480V1 = 690 V
V2 = V
2.Easy
N1​ = 8000N2​ = 2009200 VV2​ = ?

An ideal transformer has 8000 turns on its primary winding and 200 turns on its secondary winding. The primary is connected to a 9200 V AC supply. Find the secondary voltage V2.

N1 = 8000N2 = 200V1 = 9200 V
V2 = V
3.Medium
RL​ = 4 Ω41920 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 920 V applied to its primary winding. A 4 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 4:1V1 = 920 VRL = 4 Ω
I1 = A
4.Medium
50 ΩN1​N2​450 Ω

An amplifier with an output resistance of 450 Ω drives a 50 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 450 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 450 ΩRL = 50 Ω
a =
5.Hard
25 kVA

A single-phase 25 kVA transformer has a core loss of 125 W and a copper loss of 187.5 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 25 kVAPcore = 125 WPcu,fl = 187.5 W
Sη,max = kVA
6.Hard
pf 0.9550 kVA, 75% load

A single-phase 50 kVA transformer has a core loss of 250 W and a copper loss of 1000 W at rated load. It supplies 75% 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 = 1000 Wx = 0.75pf = 0.95
Ploss = W

Answer key

  1. 1. V2 = 5520 V
  2. 2. V2 = 230 V
  3. 3. I1 = 14.38 A
  4. 4. a = 3
  5. 5. Sη,max = 20.41 kVA
  6. 6. Ploss = 812.5 W

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