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 1280 turns on its primary winding and 80 turns on its secondary winding. The primary is connected to a 3840 V AC supply. Find the secondary voltage V₂.

N₁ = 1280N₂ = 80V₁ = 3840 V

V₂ = V

2.Easy

An ideal transformer has 60 turns on its primary winding and 480 turns on its secondary winding. The primary is connected to a 120 V AC supply. Find the secondary voltage V₂.

N₁ = 60N₂ = 480V₁ = 120 V

V₂ = V

3.Medium

A single-phase 250 kVA, 10000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 250 kVAV₁ = 10000 VV₂ = 400 V

I_HV = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 480 V applied to its primary winding. A 6 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 480 VR_L = 6 Ω

I₁ = A

5.Hard

A single-phase 250 kVA transformer has a core loss of 1250 W and a copper loss of 2500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 250 kVAP_core = 1250 WP_cu,fl = 2500 W

S_η,max = kVA

6.Hard

A single-phase 75 kVA transformer has a core loss of 300 W and a copper loss of 900 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 = 75 kVAP_core = 300 WP_cu,fl = 900 Wx = 0.5pf = 0.9

P_loss = W

Answer key

1. V₂ = 240 V
2. V₂ = 960 V
3. I_HV = 25 A
4. I₁ = 20 A
5. S_η,max = 176.8 kVA
6. P_loss = 525 W

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