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​ = 200N2​ = 50480 VV2​ = ?

An ideal transformer has 200 turns on its primary winding and 50 turns on its secondary winding. The primary is connected to a 480 V AC supply. Find the secondary voltage V2.

N1 = 200N2 = 50V1 = 480 V
V2 = V
2.Easy
N1​ = 1000N2​ = ?6000 V240 V

An ideal transformer must step 6000 V down to 240 V. Its primary winding has 1000 turns. How many turns N2 does the secondary winding need?

V1 = 6000 VV2 = 240 VN1 = 1000
N2 =
3.Medium
RL​ = 15 Ω41480 VV2​I1​ = ?I2​

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 480 V applied to its primary winding. A 15 Ω resistor is connected across the secondary winding. Find the primary current I1.

N1:N2 = 4:1V1 = 480 VRL = 15 Ω
I1 = A
4.Medium
4800 V240 VIHV​ILV​ = ?75 kVA

A single-phase 75 kVA, 4800/240 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 75 kVAV1 = 4800 VV2 = 240 V
ILV = A
5.Hard
pf 0.8250 kVA, 25% load

A single-phase 250 kVA transformer has a core loss of 2000 W and a copper loss of 3000 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 = 250 kVAPcore = 2000 WPcu,fl = 3000 Wx = 0.25pf = 0.8
Ploss = W
6.Hard
pf 0.8100 kVA, η = 96.5%

A single-phase 100 kVA transformer has a core loss of 800 W. At rated load and a power factor of 0.8 lagging its efficiency is 96.5%. Find the full-load copper loss Pcu,fl in watts.

S = 100 kVAPcore = 800 Wpf = 0.8η = 96.5%
Pcu,fl = W

Answer key

  1. 1. V2 = 120 V
  2. 2. N2 = 40
  3. 3. I1 = 2 A
  4. 4. ILV = 312.5 A
  5. 5. Ploss = 2188 W
  6. 6. Pcu,fl = 2102 W

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