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​ = ?8000 V400 V

An ideal transformer must step 8000 V down to 400 V. Its primary winding has 4000 turns. How many turns N2 does the secondary winding need?

V1 = 8000 VV2 = 400 VN1 = 4000
N2 =
2.Easy
N1​ = 120N2​ = 240120 VV2​ = ?

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

N1 = 120N2 = 240V1 = 120 V
V2 = V
3.Medium
16 Ω51

A 16 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 5:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 5:1RL = 16 Ω
R1′ = Ω
4.Medium
8 Ω51

An 8 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 5:1. Find the resistance R1′ seen looking into the primary winding.

N1:N2 = 5:1RL = 8 Ω
R1′ = Ω
5.Hard
pf 0.85250 kVA, 50% load

A single-phase 250 kVA transformer has a core loss of 2000 W and a copper loss of 8000 W at rated load. It supplies 50% 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 = 2000 WPcu,fl = 8000 Wx = 0.5pf = 0.85
Ploss = W
6.Hard
pf 0.8500 kVA, 25% load

A single-phase 500 kVA transformer has a core loss of 3000 W and a copper loss of 6000 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 = 500 kVAPcore = 3000 WPcu,fl = 6000 Wx = 0.25pf = 0.8
Ploss = W

Answer key

  1. 1. N2 = 200
  2. 2. V2 = 240 V
  3. 3. R1′ = 400 Ω
  4. 4. R1′ = 200 Ω
  5. 5. Ploss = 4000 W
  6. 6. Ploss = 3375 W

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