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​ = 4000N2​ = ?6000 V120 V

An ideal transformer must step 6000 V down to 120 V. Its primary winding has 4000 turns. How many turns N2 does the secondary winding need?

V1 = 6000 VV2 = 120 VN1 = 4000
N2 =
2.Easy
N1​ = 120N2​ = 240690 VV2​ = ?

An ideal transformer has 120 turns on its primary winding and 240 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V2.

N1 = 120N2 = 240V1 = 690 V
V2 = V
3.Medium
8 Ω81

An 8 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 8:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 8:1RL = 8 Ω
R1′ = Ω
4.Medium
5 ΩN1​N2​125 Ω

An amplifier with an output resistance of 125 Ω drives a 5 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 125 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

Rs = 125 ΩRL = 5 Ω
a =
5.Hard
pf 0.8200 kVA, 25% load

A single-phase 200 kVA transformer has a core loss of 800 W and a copper loss of 1600 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.8 lagging. Find the total losses Ploss in watts at this load.

S = 200 kVAPcore = 800 WPcu,fl = 1600 Wx = 0.25pf = 0.8
Ploss = W
6.Hard
pf 0.95250 kVA, 75% load

A single-phase 250 kVA transformer has a core loss of 1250 W and a copper loss of 3750 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 = 250 kVAPcore = 1250 WPcu,fl = 3750 Wx = 0.75pf = 0.95
Ploss = W

Answer key

  1. 1. N2 = 80
  2. 2. V2 = 1380 V
  3. 3. R1′ = 512 Ω
  4. 4. a = 5
  5. 5. Ploss = 900 W
  6. 6. Ploss = 3359 W

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