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​ = 625N2​ = ?10000 V400 V

An ideal transformer must step 10000 V down to 400 V. Its primary winding has 625 turns. How many turns N2 does the secondary winding need?

V1 = 10000 VV2 = 400 VN1 = 625
N2 =
2.Easy
N1​ = 250N2​ = 2000120 VV2​ = ?

An ideal transformer has 250 turns on its primary winding and 2000 turns on its secondary winding. The primary is connected to a 120 V AC supply. Find the secondary voltage V2.

N1 = 250N2 = 2000V1 = 120 V
V2 = V
3.Medium
7200 V240 VIHV​ILV​ = ?75 kVA

A single-phase 75 kVA, 7200/240 V transformer operates at its rated load. Treat it as ideal. Find the current ILV in the low-voltage winding.

S = 75 kVAV1 = 7200 VV2 = 240 V
ILV = A
4.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
5.Hard
75 kVA

A single-phase 75 kVA transformer has a core loss of 375 W and a copper loss of 937.5 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 75 kVAPcore = 375 WPcu,fl = 937.5 W
Sη,max = kVA
6.Hard
200 kVA

A single-phase 200 kVA transformer has a core loss of 1000 W and a copper loss of 2500 W at rated load. At what load Sη,max, in kVA, is its efficiency highest?

S = 200 kVAPcore = 1000 WPcu,fl = 2500 W
Sη,max = kVA

Answer key

  1. 1. N2 = 25
  2. 2. V2 = 960 V
  3. 3. ILV = 312.5 A
  4. 4. R1′ = 640 Ω
  5. 5. Sη,max = 47.43 kVA
  6. 6. Sη,max = 126.5 kVA

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