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 120 turns on its primary winding and 2400 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 120N₂ = 2400V₁ = 400 V

V₂ = V

2.Easy

An ideal transformer has 320 turns on its primary winding and 40 turns on its secondary winding. The primary is connected to a 960 V AC supply. Find the secondary voltage V₂.

N₁ = 320N₂ = 40V₁ = 960 V

V₂ = V

3.Medium

A single-phase 150 kVA, 7200/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 150 kVAV₁ = 7200 VV₂ = 240 V

I_LV = A

4.Medium

A single-phase 75 kVA, 7200/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 75 kVAV₁ = 7200 VV₂ = 240 V

I_LV = A

5.Hard

A single-phase 100 kVA transformer has a core loss of 800 W. At rated load and a power factor of 0.85 lagging its efficiency is 97%. Find the full-load copper loss P_cu,fl in watts.

S = 100 kVAP_core = 800 Wpf = 0.85η = 97%

P_cu,fl = W

6.Hard

A single-phase 500 kVA transformer has a core loss of 3000 W and a copper loss of 4500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 3000 WP_cu,fl = 4500 W

S_η,max = kVA

Answer key

1. V₂ = 8000 V
2. V₂ = 120 V
3. I_LV = 625 A
4. I_LV = 312.5 A
5. P_cu,fl = 1829 W
6. S_η,max = 408.2 kVA

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