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 must step 920 V down to 230 V. Its primary winding has 160 turns. How many turns N₂ does the secondary winding need?

V₁ = 920 VV₂ = 230 VN₁ = 160

N₂ =

2.Easy

An ideal transformer has 60 turns on its primary winding and 1200 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 60N₂ = 1200V₁ = 690 V

V₂ = V

3.Medium

A 4 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 = 4 Ω

R_1′ = Ω

4.Medium

An 8 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 = 8 Ω

R_1′ = Ω

5.Hard

A single-phase 500 kVA transformer has a core loss of 2000 W and a copper loss of 5000 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.8 lagging. Find the total losses P_loss in watts at this load.

S = 500 kVAP_core = 2000 WP_cu,fl = 5000 Wx = 0.25pf = 0.8

P_loss = W

6.Hard

A single-phase 75 kVA transformer has a core loss of 225 W and a copper loss of 675 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 225 WP_cu,fl = 675 W

S_η,max = kVA

Answer key

1. N₂ = 40
2. V₂ = 13800 V
3. R_1′ = 256 Ω
4. R_1′ = 512 Ω
5. P_loss = 2313 W
6. S_η,max = 43.3 kVA

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