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 100 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 2000 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 20V₁ = 2000 V

V₂ = V

2.Easy

An ideal transformer has 3000 turns on its primary winding and 120 turns on its secondary winding. The primary is connected to a 5750 V AC supply. Find the secondary voltage V₂.

N₁ = 3000N₂ = 120V₁ = 5750 V

V₂ = V

3.Medium

A 5 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 12:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 12:1R_L = 5 Ω

R_1′ = Ω

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 460 V applied to its primary winding. A 48 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 460 VR_L = 48 Ω

I₁ = A

5.Hard

A single-phase 75 kVA transformer has a core loss of 450 W and a copper loss of 1800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 450 WP_cu,fl = 1800 W

S_η,max = kVA

6.Hard

A single-phase 100 kVA transformer has a core loss of 600 W and a copper loss of 1800 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 = 100 kVAP_core = 600 WP_cu,fl = 1800 Wx = 0.75pf = 0.9

P_loss = W

Answer key

1. V₂ = 400 V
2. V₂ = 230 V
3. R_1′ = 720 Ω
4. I₁ = 2.396 A
5. S_η,max = 37.5 kVA
6. P_loss = 1613 W

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