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 80 turns on its primary winding and 160 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 160V₁ = 400 V

V₂ = V

2.Easy

An ideal transformer must step 2300 V down to 230 V. Its primary winding has 1000 turns. How many turns N₂ does the secondary winding need?

V₁ = 2300 VV₂ = 230 VN₁ = 1000

N₂ =

3.Medium

A single-phase 10 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 10 kVAV₁ = 2400 VV₂ = 240 V

I_HV = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 20:1 has 4800 V applied to its primary winding. A 30 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 20:1V₁ = 4800 VR_L = 30 Ω

I₁ = A

5.Hard

A single-phase 200 kVA transformer has a core loss of 800 W. At rated load and a power factor of 0.85 lagging its efficiency is 99%. Find the full-load copper loss P_cu,fl in watts.

S = 200 kVAP_core = 800 Wpf = 0.85η = 99%

P_cu,fl = W

6.Hard

A single-phase 250 kVA transformer has a core loss of 1500 W and a copper loss of 4500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 250 kVAP_core = 1500 WP_cu,fl = 4500 W

S_η,max = kVA

Answer key

1. V₂ = 800 V
2. N₂ = 100
3. I_HV = 4.167 A
4. I₁ = 0.4 A
5. P_cu,fl = 917.2 W
6. S_η,max = 144.3 kVA

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