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 2300 V down to 230 V. Its primary winding has 1500 turns. How many turns N₂ does the secondary winding need?

V₁ = 2300 VV₂ = 230 VN₁ = 1500

N₂ =

2.Easy

An ideal transformer has 100 turns on its primary winding and 2500 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 2500V₁ = 400 V

V₂ = V

3.Medium

A single-phase 50 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 = 50 kVAV₁ = 10000 VV₂ = 400 V

I_HV = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 920 V applied to its primary winding. A 12 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 4:1V₁ = 920 VR_L = 12 Ω

I₁ = A

5.Hard

A single-phase 150 kVA transformer has a core loss of 900 W. At rated load and a power factor of 0.95 lagging its efficiency is 98.2%. Find the full-load copper loss P_cu,fl in watts.

S = 150 kVAP_core = 900 Wpf = 0.95η = 98.2%

P_cu,fl = W

6.Hard

A single-phase 50 kVA transformer has a core loss of 250 W and a copper loss of 1000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 50 kVAP_core = 250 WP_cu,fl = 1000 W

S_η,max = kVA

Answer key

1. N₂ = 150
2. V₂ = 10000 V
3. I_HV = 5 A
4. I₁ = 4.792 A
5. P_cu,fl = 1712 W
6. S_η,max = 25 kVA

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