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

An ideal transformer must step 6000 V down to 240 V. Its primary winding has 5000 turns. How many turns N₂ does the secondary winding need?

V₁ = 6000 VV₂ = 240 VN₁ = 5000

N₂ =

2.Easy

An ideal transformer has 250 turns on its primary winding and 1250 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 250N₂ = 1250V₁ = 400 V

V₂ = V

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 480 V applied to its primary winding. A 6 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 480 VR_L = 6 Ω

I₁ = A

4.Medium

A 10 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 12:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 12:1R_L = 10 Ω

R_1′ = Ω

5.Hard

A single-phase 250 kVA transformer has a core loss of 750 W. At rated load and a power factor of 0.85 lagging its efficiency is 98.8%. Find the full-load copper loss P_cu,fl in watts.

S = 250 kVAP_core = 750 Wpf = 0.85η = 98.8%

P_cu,fl = W

6.Hard

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 97%. Find the full-load copper loss P_cu,fl in watts.

S = 25 kVAP_core = 125 Wpf = 0.9η = 97%

P_cu,fl = W

Answer key

1. N₂ = 200
2. V₂ = 2000 V
3. I₁ = 20 A
4. R_1′ = 1440 Ω
5. P_cu,fl = 1831 W
6. P_cu,fl = 570.9 W

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