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 3840 V down to 240 V. Its primary winding has 1920 turns. How many turns N₂ does the secondary winding need?

V₁ = 3840 VV₂ = 240 VN₁ = 1920

N₂ =

2.Easy

An ideal transformer has 250 turns on its primary winding and 5000 turns on its secondary winding. The primary is connected to a 110 V AC supply. Find the secondary voltage V₂.

N₁ = 250N₂ = 5000V₁ = 110 V

V₂ = V

3.Medium

A single-phase 50 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 50 kVAV₁ = 2400 VV₂ = 240 V

I_LV = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 460 V applied to its primary winding. A 48 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 460 VR_L = 48 Ω

I₁ = A

5.Hard

A single-phase 50 kVA transformer has a core loss of 150 W. At rated load and a power factor of 0.85 lagging its efficiency is 97.5%. Find the full-load copper loss P_cu,fl in watts.

S = 50 kVAP_core = 150 Wpf = 0.85η = 97.5%

P_cu,fl = W

6.Hard

A single-phase 250 kVA transformer has a core loss of 1000 W and a copper loss of 3000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 250 kVAP_core = 1000 WP_cu,fl = 3000 W

S_η,max = kVA

Answer key

1. N₂ = 120
2. V₂ = 2200 V
3. I_LV = 208.3 A
4. I₁ = 2.396 A
5. P_cu,fl = 939.7 W
6. S_η,max = 144.3 kVA

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