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 100 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 1200 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 20V₁ = 1200 V

V₂ = V

2.Easy

An ideal transformer has 2500 turns on its primary winding and 50 turns on its secondary winding. The primary is connected to a 12000 V AC supply. Find the secondary voltage V₂.

N₁ = 2500N₂ = 50V₁ = 12000 V

V₂ = V

3.Medium

A single-phase 250 kVA, 11000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 250 kVAV₁ = 11000 VV₂ = 400 V

I_LV = A

4.Medium

An amplifier with an output resistance of 400 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 400 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 400 ΩR_L = 4 Ω

a =

5.Hard

A single-phase 500 kVA transformer has a core loss of 2500 W and a copper loss of 10000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 2500 WP_cu,fl = 10000 W

S_η,max = kVA

6.Hard

A single-phase 25 kVA transformer has a core loss of 75 W and a copper loss of 187.5 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 25 kVAP_core = 75 WP_cu,fl = 187.5 W

S_η,max = kVA

Answer key

1. V₂ = 240 V
2. V₂ = 240 V
3. I_LV = 625 A
4. a = 10
5. S_η,max = 250 kVA
6. S_η,max = 15.81 kVA

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