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 2400 turns on its primary winding and 60 turns on its secondary winding. The primary is connected to a 4800 V AC supply. Find the secondary voltage V₂.

N₁ = 2400N₂ = 60V₁ = 4800 V

V₂ = V

2.Easy

An ideal transformer must step 2300 V down to 230 V. Its primary winding has 600 turns. How many turns N₂ does the secondary winding need?

V₁ = 2300 VV₂ = 230 VN₁ = 600

N₂ =

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 920 V applied to its primary winding. A 5 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 4:1V₁ = 920 VR_L = 5 Ω

I₁ = A

4.Medium

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

S = 150 kVAV₁ = 7200 VV₂ = 240 V

I_HV = A

5.Hard

A single-phase 75 kVA transformer has a core loss of 600 W and a copper loss of 900 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 600 WP_cu,fl = 900 W

S_η,max = kVA

6.Hard

A single-phase 500 kVA transformer has a core loss of 2000 W. At rated load and a power factor of 0.9 lagging its efficiency is 96%. Find the full-load copper loss P_cu,fl in watts.

S = 500 kVAP_core = 2000 Wpf = 0.9η = 96%

P_cu,fl = W

Answer key

1. V₂ = 120 V
2. N₂ = 60
3. I₁ = 11.5 A
4. I_HV = 20.83 A
5. S_η,max = 61.24 kVA
6. P_cu,fl = 16750 W

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