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 230 V AC supply. Find the secondary voltage V₂.

N₁ = 200N₂ = 2000V₁ = 230 V

V₂ = V

2.Easy

An ideal transformer has 100 turns on its primary winding and 500 turns on its secondary winding. The primary is connected to a 240 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 500V₁ = 240 V

V₂ = V

3.Medium

A 75 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 3:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 3:1R_L = 75 Ω

R_1′ = Ω

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 20:1 has 2400 V applied to its primary winding. A 15 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 20:1V₁ = 2400 VR_L = 15 Ω

I₁ = A

5.Hard

A single-phase 50 kVA transformer has a core loss of 150 W and a copper loss of 450 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 50 kVAP_core = 150 WP_cu,fl = 450 W

S_η,max = kVA

6.Hard

A single-phase 25 kVA transformer has a core loss of 75 W and a copper loss of 225 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.9 lagging. Find the total losses P_loss in watts at this load.

S = 25 kVAP_core = 75 WP_cu,fl = 225 Wx = 0.5pf = 0.9

P_loss = W

Answer key

1. V₂ = 2300 V
2. V₂ = 1200 V
3. R_1′ = 675 Ω
4. I₁ = 0.4 A
5. S_η,max = 28.87 kVA
6. P_loss = 131.3 W

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