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 1600 turns on its primary winding and 200 turns on its secondary winding. The primary is connected to a 960 V AC supply. Find the secondary voltage V₂.

N₁ = 1600N₂ = 200V₁ = 960 V

V₂ = V

2.Easy

An ideal transformer must step 460 V down to 230 V. Its primary winding has 50 turns. How many turns N₂ does the secondary winding need?

V₁ = 460 VV₂ = 230 VN₁ = 50

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 ideal transformer with a turns ratio N₁:N₂ = 20:1 has 4800 V applied to its primary winding. A 24 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 20:1V₁ = 4800 VR_L = 24 Ω

I₁ = A

5.Hard

A single-phase 500 kVA transformer has a core loss of 2500 W and a copper loss of 7500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 2500 WP_cu,fl = 7500 W

S_η,max = kVA

6.Hard

A single-phase 50 kVA transformer has a core loss of 150 W and a copper loss of 225 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.95 lagging. Find the total losses P_loss in watts at this load.

S = 50 kVAP_core = 150 WP_cu,fl = 225 Wx = 0.75pf = 0.95

P_loss = W

Answer key

1. V₂ = 120 V
2. N₂ = 25
3. a = 2
4. I₁ = 0.5 A
5. S_η,max = 288.7 kVA
6. P_loss = 276.6 W

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