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 460 V down to 230 V. Its primary winding has 120 turns. How many turns N₂ does the secondary winding need?

V₁ = 460 VV₂ = 230 VN₁ = 120

N₂ =

2.Easy

An ideal transformer has 800 turns on its primary winding and 100 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V₂.

N₁ = 800N₂ = 100V₁ = 1920 V

V₂ = V

3.Medium

A 2 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 = 2 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 4 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 480 VR_L = 4 Ω

I₁ = A

5.Hard

A single-phase 25 kVA transformer has a core loss of 100 W and a copper loss of 150 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.95 lagging. Find the total losses P_loss in watts at this load.

S = 25 kVAP_core = 100 WP_cu,fl = 150 Wx = 0.75pf = 0.95

P_loss = W

6.Hard

A single-phase 150 kVA transformer has a core loss of 900 W and a copper loss of 1800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 150 kVAP_core = 900 WP_cu,fl = 1800 W

S_η,max = kVA

Answer key

1. N₂ = 60
2. V₂ = 240 V
3. R_1′ = 50 Ω
4. I₁ = 30 A
5. P_loss = 184.4 W
6. S_η,max = 106.1 kVA

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