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 960 V down to 120 V. Its primary winding has 1200 turns. How many turns N₂ does the secondary winding need?

V₁ = 960 VV₂ = 120 VN₁ = 1200

N₂ =

2.Easy

An ideal transformer must step 6000 V down to 240 V. Its primary winding has 3000 turns. How many turns N₂ does the secondary winding need?

V₁ = 6000 VV₂ = 240 VN₁ = 3000

N₂ =

3.Medium

A 2 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 5:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 5:1R_L = 2 Ω

R_1′ = Ω

4.Medium

An amplifier with an output resistance of 320 Ω drives a 5 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 320 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 320 ΩR_L = 5 Ω

a =

5.Hard

A single-phase 500 kVA transformer has a core loss of 2000 W and a copper loss of 4000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 2000 WP_cu,fl = 4000 W

S_η,max = kVA

6.Hard

A single-phase 250 kVA transformer has a core loss of 1250 W and a copper loss of 1875 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.9 lagging. Find the total losses P_loss in watts at this load.

S = 250 kVAP_core = 1250 WP_cu,fl = 1875 Wx = 0.75pf = 0.9

P_loss = W

Answer key

1. N₂ = 150
2. N₂ = 120
3. R_1′ = 50 Ω
4. a = 8
5. S_η,max = 353.6 kVA
6. P_loss = 2305 W

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