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 1000 turns on its primary winding and 50 turns on its secondary winding. The primary is connected to a 2400 V AC supply. Find the secondary voltage V₂.

N₁ = 1000N₂ = 50V₁ = 2400 V

V₂ = V

2.Easy

An ideal transformer has 200 turns on its primary winding and 1000 turns on its secondary winding. The primary is connected to a 240 V AC supply. Find the secondary voltage V₂.

N₁ = 200N₂ = 1000V₁ = 240 V

V₂ = V

3.Medium

An amplifier with an output resistance of 400 Ω drives a 4 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 400 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 400 ΩR_L = 4 Ω

a =

4.Medium

A single-phase 15 kVA, 480/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 15 kVAV₁ = 480 VV₂ = 240 V

I_HV = A

5.Hard

A single-phase 75 kVA transformer has a core loss of 600 W and a copper loss of 2400 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 600 WP_cu,fl = 2400 W

S_η,max = kVA

6.Hard

A single-phase 100 kVA transformer has a core loss of 500 W and a copper loss of 750 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.9 lagging. Find the total losses P_loss in watts at this load.

S = 100 kVAP_core = 500 WP_cu,fl = 750 Wx = 0.25pf = 0.9

P_loss = W

Answer key

1. V₂ = 120 V
2. V₂ = 1200 V
3. a = 10
4. I_HV = 31.25 A
5. S_η,max = 37.5 kVA
6. P_loss = 546.9 W

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