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 100 turns on its primary winding and 800 turns on its secondary winding. The primary is connected to a 110 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 800V₁ = 110 V

V₂ = V

2.Easy

An ideal transformer has 200 turns on its primary winding and 5000 turns on its secondary winding. The primary is connected to a 120 V AC supply. Find the secondary voltage V₂.

N₁ = 200N₂ = 5000V₁ = 120 V

V₂ = V

3.Medium

An amplifier with an output resistance of 128 Ω drives an 8 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 128 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 128 ΩR_L = 8 Ω

a =

4.Medium

A single-phase 250 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 250 kVAV₁ = 2400 VV₂ = 240 V

I_LV = A

5.Hard

A single-phase 250 kVA transformer has a core loss of 1500 W and a copper loss of 3000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 250 kVAP_core = 1500 WP_cu,fl = 3000 W

S_η,max = kVA

6.Hard

A single-phase 150 kVA transformer has a core loss of 900 W and a copper loss of 3600 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 = 150 kVAP_core = 900 WP_cu,fl = 3600 Wx = 0.75pf = 0.95

P_loss = W

Answer key

1. V₂ = 880 V
2. V₂ = 3000 V
3. a = 4
4. I_LV = 1042 A
5. S_η,max = 176.8 kVA
6. P_loss = 2925 W

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