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 460 V down to 230 V. Its primary winding has 300 turns. How many turns N₂ does the secondary winding need?

V₁ = 460 VV₂ = 230 VN₁ = 300

N₂ =

2.Easy

An ideal transformer must step 800 V down to 400 V. Its primary winding has 120 turns. How many turns N₂ does the secondary winding need?

V₁ = 800 VV₂ = 400 VN₁ = 120

N₂ =

3.Medium

An amplifier with an output resistance of 288 Ω drives an 8 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 288 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 288 ΩR_L = 8 Ω

a =

4.Medium

A 16 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 8:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 8:1R_L = 16 Ω

R_1′ = Ω

5.Hard

A single-phase 100 kVA transformer has a core loss of 500 W and a copper loss of 750 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.95 lagging. Find the total losses P_loss in watts at this load.

S = 100 kVAP_core = 500 WP_cu,fl = 750 Wx = 0.5pf = 0.95

P_loss = W

6.Hard

A single-phase 75 kVA transformer has a core loss of 225 W and a copper loss of 450 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 225 WP_cu,fl = 450 W

S_η,max = kVA

Answer key

1. N₂ = 150
2. N₂ = 60
3. a = 6
4. R_1′ = 1024 Ω
5. P_loss = 687.5 W
6. S_η,max = 53.03 kVA

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