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 60 turns on its primary winding and 480 turns on its secondary winding. The primary is connected to a 240 V AC supply. Find the secondary voltage V₂.

N₁ = 60N₂ = 480V₁ = 240 V

V₂ = V

2.Easy

An ideal transformer must step 1920 V down to 240 V. Its primary winding has 200 turns. How many turns N₂ does the secondary winding need?

V₁ = 1920 VV₂ = 240 VN₁ = 200

N₂ =

3.Medium

An amplifier with an output resistance of 160 Ω drives a 10 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 160 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 160 ΩR_L = 10 Ω

a =

4.Medium

A 2 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 = 2 Ω

R_1′ = Ω

5.Hard

A single-phase 200 kVA transformer has a core loss of 1000 W and a copper loss of 2500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 1000 WP_cu,fl = 2500 W

S_η,max = kVA

6.Hard

A single-phase 250 kVA transformer has a core loss of 1000 W and a copper loss of 3000 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.8 lagging. Find the total losses P_loss in watts at this load.

S = 250 kVAP_core = 1000 WP_cu,fl = 3000 Wx = 0.75pf = 0.8

P_loss = W

Answer key

1. V₂ = 1920 V
2. N₂ = 25
3. a = 4
4. R_1′ = 128 Ω
5. S_η,max = 126.5 kVA
6. P_loss = 2688 W

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