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​ = 1280N2​ = ?3840 V240 V

An ideal transformer must step 3840 V down to 240 V. Its primary winding has 1280 turns. How many turns N2 does the secondary winding need?

V1 = 3840 VV2 = 240 VN1 = 1280
N2 =
2.Easy
N1​ = 150N2​ = 1200110 VV2​ = ?

An ideal transformer has 150 turns on its primary winding and 1200 turns on its secondary winding. The primary is connected to a 110 V AC supply. Find the secondary voltage V2.

N1 = 150N2 = 1200V1 = 110 V
V2 = V
3.Medium
10000 V400 VIHV​ = ?ILV​500 kVA

A single-phase 500 kVA, 10000/400 V transformer operates at its rated load. Treat it as ideal. Find the current IHV in the high-voltage winding.

S = 500 kVAV1 = 10000 VV2 = 400 V
IHV = A
4.Medium
RL​ = 48 Ω21460 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 460 V applied to its primary winding. A 48 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 2:1V1 = 460 VRL = 48 Ω
I1 = A
5.Hard
pf 0.925 kVA, η = 98.8%

A single-phase 25 kVA transformer has a core loss of 125 W. At rated load and a power factor of 0.9 lagging its efficiency is 98.8%. Find the full-load copper loss Pcu,fl in watts.

S = 25 kVAPcore = 125 Wpf = 0.9η = 98.8%
Pcu,fl = W
6.Hard
pf 0.95200 kVA, 25% load

A single-phase 200 kVA transformer has a core loss of 1200 W and a copper loss of 2400 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.95 lagging. Find the total losses Ploss in watts at this load.

S = 200 kVAPcore = 1200 WPcu,fl = 2400 Wx = 0.25pf = 0.95
Ploss = W

Answer key

  1. 1. N2 = 80
  2. 2. V2 = 880 V
  3. 3. IHV = 50 A
  4. 4. I1 = 2.396 A
  5. 5. Pcu,fl = 148.3 W
  6. 6. Ploss = 1350 W

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