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 150 turns on its primary winding and 300 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 150N₂ = 300V₁ = 690 V

V₂ = V

2.Easy

An ideal transformer has 200 turns on its primary winding and 50 turns on its secondary winding. The primary is connected to a 960 V AC supply. Find the secondary voltage V₂.

N₁ = 200N₂ = 50V₁ = 960 V

V₂ = V

3.Medium

A 16 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 6:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 6:1R_L = 16 Ω

R_1′ = Ω

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 480 V applied to its primary winding. A 20 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 480 VR_L = 20 Ω

I₁ = A

5.Hard

A single-phase 250 kVA transformer has a core loss of 2000 W and a copper loss of 4000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 250 kVAP_core = 2000 WP_cu,fl = 4000 W

S_η,max = kVA

6.Hard

A single-phase 200 kVA transformer has a core loss of 1600 W and a copper loss of 4800 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.9 lagging. Find the total losses P_loss in watts at this load.

S = 200 kVAP_core = 1600 WP_cu,fl = 4800 Wx = 0.75pf = 0.9

P_loss = W

Answer key

1. V₂ = 1380 V
2. V₂ = 240 V
3. R_1′ = 576 Ω
4. I₁ = 6 A
5. S_η,max = 176.8 kVA
6. P_loss = 4300 W

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