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 1920 V down to 120 V. Its primary winding has 960 turns. How many turns N₂ does the secondary winding need?

V₁ = 1920 VV₂ = 120 VN₁ = 960

N₂ =

2.Easy

An ideal transformer has 40 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 460 V AC supply. Find the secondary voltage V₂.

N₁ = 40N₂ = 20V₁ = 460 V

V₂ = V

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 2300 V applied to its primary winding. A 4 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 10:1V₁ = 2300 VR_L = 4 Ω

I₁ = A

4.Medium

A 75 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 8:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 8:1R_L = 75 Ω

R_1′ = Ω

5.Hard

A single-phase 500 kVA transformer has a core loss of 2500 W. At rated load and a power factor of 0.9 lagging its efficiency is 97.5%. Find the full-load copper loss P_cu,fl in watts.

S = 500 kVAP_core = 2500 Wpf = 0.9η = 97.5%

P_cu,fl = W

6.Hard

A single-phase 200 kVA transformer has a core loss of 1000 W and a copper loss of 2500 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.8 lagging. Find the total losses P_loss in watts at this load.

S = 200 kVAP_core = 1000 WP_cu,fl = 2500 Wx = 0.75pf = 0.8

P_loss = W

Answer key

1. N₂ = 60
2. V₂ = 230 V
3. I₁ = 5.75 A
4. R_1′ = 4800 Ω
5. P_cu,fl = 9038 W
6. P_loss = 2406 W

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