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​ = 1920N2​ = ?3840 V240 V

An ideal transformer must step 3840 V down to 240 V. Its primary winding has 1920 turns. How many turns N2 does the secondary winding need?

V1 = 3840 VV2 = 240 VN1 = 1920
N2 =
2.Easy
N1​ = 600N2​ = ?960 V240 V

An ideal transformer must step 960 V down to 240 V. Its primary winding has 600 turns. How many turns N2 does the secondary winding need?

V1 = 960 VV2 = 240 VN1 = 600
N2 =
3.Medium
RL​ = 4 Ω41480 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 480 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 = 480 VRL = 4 Ω
I1 = A
4.Medium
RL​ = 20 Ω21460 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 460 V applied to its primary winding. A 20 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 2:1V1 = 460 VRL = 20 Ω
I1 = A
5.Hard
200 kVA

A single-phase 200 kVA transformer has a core loss of 1600 W and a copper loss of 3200 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 200 kVAPcore = 1600 WPcu,fl = 3200 W
Sη,max = kVA
6.Hard
pf 0.9575 kVA, 50% load

A single-phase 75 kVA transformer has a core loss of 450 W and a copper loss of 1125 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.95 lagging. Find the total losses Ploss in watts at this load.

S = 75 kVAPcore = 450 WPcu,fl = 1125 Wx = 0.5pf = 0.95
Ploss = W

Answer key

  1. 1. N2 = 120
  2. 2. N2 = 150
  3. 3. I1 = 7.5 A
  4. 4. I1 = 5.75 A
  5. 5. Sη,max = 141.4 kVA
  6. 6. Ploss = 731.3 W

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