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 600 V down to 120 V. Its primary winding has 250 turns. How many turns N₂ does the secondary winding need?

V₁ = 600 VV₂ = 120 VN₁ = 250

N₂ =

2.Easy

An ideal transformer has 1600 turns on its primary winding and 200 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V₂.

N₁ = 1600N₂ = 200V₁ = 1920 V

V₂ = V

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 460 V applied to its primary winding. A 5 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 460 VR_L = 5 Ω

I₁ = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 480 V applied to its primary winding. An 8 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 480 VR_L = 8 Ω

I₁ = A

5.Hard

A single-phase 200 kVA transformer has a core loss of 600 W and a copper loss of 1800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 600 WP_cu,fl = 1800 W

S_η,max = kVA

6.Hard

A single-phase 150 kVA transformer has a core loss of 450 W and a copper loss of 1350 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 = 150 kVAP_core = 450 WP_cu,fl = 1350 Wx = 0.5pf = 0.9

P_loss = W

Answer key

1. N₂ = 50
2. V₂ = 240 V
3. I₁ = 23 A
4. I₁ = 15 A
5. S_η,max = 115.5 kVA
6. P_loss = 787.5 W

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