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​ = 500N2​ = ?1200 V240 V

An ideal transformer must step 1200 V down to 240 V. Its primary winding has 500 turns. How many turns N2 does the secondary winding need?

V1 = 1200 VV2 = 240 VN1 = 500
N2 =
2.Easy
N1​ = 250N2​ = 252300 VV2​ = ?

An ideal transformer has 250 turns on its primary winding and 25 turns on its secondary winding. The primary is connected to a 2300 V AC supply. Find the secondary voltage V2.

N1 = 250N2 = 25V1 = 2300 V
V2 = V
3.Medium
10 Ω81

A 10 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 = 10 Ω
R1′ = Ω
4.Medium
4160 V480 VIHV​ILV​ = ?25 kVA

A single-phase 25 kVA, 4160/480 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 25 kVAV1 = 4160 VV2 = 480 V
ILV = A
5.Hard
pf 0.9550 kVA, 75% load

A single-phase 50 kVA transformer has a core loss of 150 W and a copper loss of 375 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 = 50 kVAPcore = 150 WPcu,fl = 375 Wx = 0.75pf = 0.95
Ploss = W
6.Hard
pf 0.850 kVA, 25% load

A single-phase 50 kVA transformer has a core loss of 300 W and a copper loss of 750 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 = 50 kVAPcore = 300 WPcu,fl = 750 Wx = 0.25pf = 0.8
Ploss = W

Answer key

  1. 1. N2 = 100
  2. 2. V2 = 230 V
  3. 3. R1′ = 640 Ω
  4. 4. ILV = 52.08 A
  5. 5. Ploss = 360.9 W
  6. 6. Ploss = 346.9 W

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