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 200 turns on its primary winding and 2000 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 200N₂ = 2000V₁ = 690 V

V₂ = V

2.Easy

An ideal transformer has 60 turns on its primary winding and 1200 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 60N₂ = 1200V₁ = 400 V

V₂ = V

3.Medium

A single-phase 25 kVA, 11000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 25 kVAV₁ = 11000 VV₂ = 400 V

I_HV = A

4.Medium

An amplifier with an output resistance of 100 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 100 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 100 ΩR_L = 4 Ω

a =

5.Hard

A single-phase 100 kVA transformer has a core loss of 500 W and a copper loss of 1250 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.85 lagging. Find the total losses P_loss in watts at this load.

S = 100 kVAP_core = 500 WP_cu,fl = 1250 Wx = 0.25pf = 0.85

P_loss = W

6.Hard

A single-phase 75 kVA transformer has a core loss of 375 W and a copper loss of 1125 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 375 WP_cu,fl = 1125 W

S_η,max = kVA

Answer key

1. V₂ = 6900 V
2. V₂ = 8000 V
3. I_HV = 2.273 A
4. a = 5
5. P_loss = 578.1 W
6. S_η,max = 43.3 kVA

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