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 80 turns on its primary winding and 800 turns on its secondary winding. The primary is connected to a 120 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 800V₁ = 120 V

V₂ = V

2.Easy

An ideal transformer has 160 turns on its primary winding and 80 turns on its secondary winding. The primary is connected to an 800 V AC supply. Find the secondary voltage V₂.

N₁ = 160N₂ = 80V₁ = 800 V

V₂ = V

3.Medium

An amplifier with an output resistance of 45 Ω drives a 5 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 45 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 45 ΩR_L = 5 Ω

a =

4.Medium

An 8 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 = 8 Ω

R_1′ = Ω

5.Hard

A single-phase 150 kVA transformer has a core loss of 900 W and a copper loss of 1800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 150 kVAP_core = 900 WP_cu,fl = 1800 W

S_η,max = kVA

6.Hard

A single-phase 25 kVA transformer has a core loss of 200 W and a copper loss of 600 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 = 25 kVAP_core = 200 WP_cu,fl = 600 Wx = 0.75pf = 0.95

P_loss = W

Answer key

1. V₂ = 1200 V
2. V₂ = 400 V
3. a = 3
4. R_1′ = 512 Ω
5. S_η,max = 106.1 kVA
6. P_loss = 537.5 W

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