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 40 turns on its secondary winding. The primary is connected to a 460 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 40V₁ = 460 V

V₂ = V

2.Easy

An ideal transformer must step 2000 V down to 400 V. Its primary winding has 750 turns. How many turns N₂ does the secondary winding need?

V₁ = 2000 VV₂ = 400 VN₁ = 750

N₂ =

3.Medium

An amplifier with an output resistance of 40 Ω drives a 10 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 40 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 40 ΩR_L = 10 Ω

a =

4.Medium

An amplifier with an output resistance of 576 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 576 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 576 ΩR_L = 4 Ω

a =

5.Hard

A single-phase 50 kVA transformer has a core loss of 400 W and a copper loss of 1200 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.85 lagging. Find the total losses P_loss in watts at this load.

S = 50 kVAP_core = 400 WP_cu,fl = 1200 Wx = 0.25pf = 0.85

P_loss = W

6.Hard

A single-phase 200 kVA transformer has a core loss of 1200 W and a copper loss of 4800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 1200 WP_cu,fl = 4800 W

S_η,max = kVA

Answer key

1. V₂ = 230 V
2. N₂ = 150
3. a = 2
4. a = 12
5. P_loss = 475 W
6. S_η,max = 100 kVA

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