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 800 turns on its primary winding and 100 turns on its secondary winding. The primary is connected to a 960 V AC supply. Find the secondary voltage V₂.

N₁ = 800N₂ = 100V₁ = 960 V

V₂ = V

2.Easy

An ideal transformer must step 5750 V down to 230 V. Its primary winding has 1500 turns. How many turns N₂ does the secondary winding need?

V₁ = 5750 VV₂ = 230 VN₁ = 1500

N₂ =

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 20:1 has 4600 V applied to its primary winding. A 5 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 20:1V₁ = 4600 VR_L = 5 Ω

I₁ = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 960 V applied to its primary winding. A 48 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 4:1V₁ = 960 VR_L = 48 Ω

I₁ = A

5.Hard

A single-phase 100 kVA transformer has a core loss of 400 W. At rated load and a power factor of 0.95 lagging its efficiency is 99%. Find the full-load copper loss P_cu,fl in watts.

S = 100 kVAP_core = 400 Wpf = 0.95η = 99%

P_cu,fl = W

6.Hard

A single-phase 200 kVA transformer has a core loss of 800 W and a copper loss of 2400 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 800 WP_cu,fl = 2400 W

S_η,max = kVA

Answer key

1. V₂ = 120 V
2. N₂ = 60
3. I₁ = 2.3 A
4. I₁ = 1.25 A
5. P_cu,fl = 559.6 W
6. S_η,max = 115.5 kVA

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