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 3000 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 150N₂ = 3000V₁ = 690 V

V₂ = V

2.Easy

An ideal transformer has 1200 turns on its primary winding and 120 turns on its secondary winding. The primary is connected to a 2300 V AC supply. Find the secondary voltage V₂.

N₁ = 1200N₂ = 120V₁ = 2300 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 = 10:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 10:1R_L = 5 Ω

R_1′ = Ω

4.Medium

A 75 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 5:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 5:1R_L = 75 Ω

R_1′ = Ω

5.Hard

A single-phase 500 kVA transformer has a core loss of 1500 W and a copper loss of 4500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 1500 WP_cu,fl = 4500 W

S_η,max = kVA

6.Hard

A single-phase 250 kVA transformer has a core loss of 1250 W and a copper loss of 5000 W at rated load. It supplies 50% 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 = 1250 WP_cu,fl = 5000 Wx = 0.5pf = 0.95

P_loss = W

Answer key

1. V₂ = 13800 V
2. V₂ = 230 V
3. R_1′ = 500 Ω
4. R_1′ = 1875 Ω
5. S_η,max = 288.7 kVA
6. P_loss = 2500 W

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