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 60 turns on its primary winding and 300 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 60N₂ = 300V₁ = 400 V

V₂ = V

2.Easy

An ideal transformer has 200 turns on its primary winding and 1600 turns on its secondary winding. The primary is connected to a 230 V AC supply. Find the secondary voltage V₂.

N₁ = 200N₂ = 1600V₁ = 230 V

V₂ = V

3.Medium

A single-phase 250 kVA, 6600/230 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 250 kVAV₁ = 6600 VV₂ = 230 V

I_LV = A

4.Medium

A 16 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 = 16 Ω

R_1′ = Ω

5.Hard

A single-phase 150 kVA transformer has a core loss of 600 W and a copper loss of 1500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 150 kVAP_core = 600 WP_cu,fl = 1500 W

S_η,max = kVA

6.Hard

A single-phase 250 kVA transformer has a core loss of 750 W and a copper loss of 1875 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.95 lagging. Find the total losses P_loss in watts at this load.

S = 250 kVAP_core = 750 WP_cu,fl = 1875 Wx = 0.25pf = 0.95

P_loss = W

Answer key

1. V₂ = 2000 V
2. V₂ = 1840 V
3. I_LV = 1087 A
4. R_1′ = 1024 Ω
5. S_η,max = 94.87 kVA
6. P_loss = 867.2 W

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