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 10000 V down to 400 V. Its primary winding has 3750 turns. How many turns N₂ does the secondary winding need?

V₁ = 10000 VV₂ = 400 VN₁ = 3750

N₂ =

2.Easy

An ideal transformer must step 6000 V down to 240 V. Its primary winding has 2500 turns. How many turns N₂ does the secondary winding need?

V₁ = 6000 VV₂ = 240 VN₁ = 2500

N₂ =

3.Medium

An amplifier with an output resistance of 128 Ω drives an 8 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 128 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 128 ΩR_L = 8 Ω

a =

4.Medium

An amplifier with an output resistance of 144 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 144 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 144 ΩR_L = 4 Ω

a =

5.Hard

A single-phase 25 kVA transformer has a core loss of 75 W. At rated load and a power factor of 0.9 lagging its efficiency is 98%. Find the full-load copper loss P_cu,fl in watts.

S = 25 kVAP_core = 75 Wpf = 0.9η = 98%

P_cu,fl = W

6.Hard

A single-phase 150 kVA transformer has a core loss of 450 W and a copper loss of 1800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 150 kVAP_core = 450 WP_cu,fl = 1800 W

S_η,max = kVA

Answer key

1. N₂ = 150
2. N₂ = 100
3. a = 4
4. a = 6
5. P_cu,fl = 384.2 W
6. S_η,max = 75 kVA

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