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 has 1600 turns on its primary winding and 200 turns on its secondary winding. The primary is connected to a 960 V AC supply. Find the secondary voltage V₂.

N₁ = 1600N₂ = 200V₁ = 960 V

V₂ = V

2.Easy

An ideal transformer must step 4800 V down to 120 V. Its primary winding has 4800 turns. How many turns N₂ does the secondary winding need?

V₁ = 4800 VV₂ = 120 VN₁ = 4800

N₂ =

3.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

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 1200 V applied to its primary winding. An 8 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 10:1V₁ = 1200 VR_L = 8 Ω

I₁ = A

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 99%. Find the full-load copper loss P_cu,fl in watts.

S = 250 kVAP_core = 750 Wpf = 0.85η = 99%

P_cu,fl = W

6.Hard

A single-phase 250 kVA transformer has a core loss of 750 W and a copper loss of 1125 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.85 lagging. Find the total losses P_loss in watts at this load.

S = 250 kVAP_core = 750 WP_cu,fl = 1125 Wx = 0.75pf = 0.85

P_loss = W

Answer key

1. V₂ = 120 V
2. N₂ = 120
3. R_1′ = 1440 Ω
4. I₁ = 1.5 A
5. P_cu,fl = 1396 W
6. P_loss = 1383 W

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