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 9200 V down to 230 V. Its primary winding has 2000 turns. How many turns N₂ does the secondary winding need?

V₁ = 9200 VV₂ = 230 VN₁ = 2000

N₂ =

2.Easy

An ideal transformer must step 3840 V down to 240 V. Its primary winding has 800 turns. How many turns N₂ does the secondary winding need?

V₁ = 3840 VV₂ = 240 VN₁ = 800

N₂ =

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 2300 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 = 2300 VR_L = 8 Ω

I₁ = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 240 V applied to its primary winding. An 8 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 240 VR_L = 8 Ω

I₁ = A

5.Hard

A single-phase 200 kVA transformer has a core loss of 1600 W and a copper loss of 4800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 1600 WP_cu,fl = 4800 W

S_η,max = kVA

6.Hard

A single-phase 200 kVA transformer has a core loss of 800 W. At rated load and a power factor of 0.8 lagging its efficiency is 98.8%. Find the full-load copper loss P_cu,fl in watts.

S = 200 kVAP_core = 800 Wpf = 0.8η = 98.8%

P_cu,fl = W

Answer key

1. N₂ = 50
2. N₂ = 50
3. I₁ = 2.875 A
4. I₁ = 7.5 A
5. S_η,max = 115.5 kVA
6. P_cu,fl = 1143 W

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