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 1920 V down to 120 V. Its primary winding has 2400 turns. How many turns N₂ does the secondary winding need?

V₁ = 1920 VV₂ = 120 VN₁ = 2400

N₂ =

2.Easy

An ideal transformer must step 1200 V down to 240 V. Its primary winding has 200 turns. How many turns N₂ does the secondary winding need?

V₁ = 1200 VV₂ = 240 VN₁ = 200

N₂ =

3.Medium

An amplifier with an output resistance of 10800 Ω drives a 75 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 10800 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 10800 ΩR_L = 75 Ω

a =

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 960 V applied to its primary winding. A 4 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 4:1V₁ = 960 VR_L = 4 Ω

I₁ = A

5.Hard

A single-phase 500 kVA transformer has a core loss of 2000 W and a copper loss of 3000 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.85 lagging. Find the total losses P_loss in watts at this load.

S = 500 kVAP_core = 2000 WP_cu,fl = 3000 Wx = 0.5pf = 0.85

P_loss = W

6.Hard

A single-phase 200 kVA transformer has a core loss of 1000 W and a copper loss of 3000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 1000 WP_cu,fl = 3000 W

S_η,max = kVA

Answer key

1. N₂ = 150
2. N₂ = 40
3. a = 12
4. I₁ = 15 A
5. P_loss = 2750 W
6. S_η,max = 115.5 kVA

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