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.

New worksheet Practise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________ Date: ____________

1.Easy

An ideal transformer must step 20000 V down to 400 V. Its primary winding has 10000 turns. How many turns N₂ does the secondary winding need?

V₁ = 20000 VV₂ = 400 VN₁ = 10000

N₂ =

2.Easy

An ideal transformer has 80 turns on its primary winding and 320 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 320V₁ = 400 V

V₂ = V

3.Medium

A single-phase 150 kVA, 4160/480 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 150 kVAV₁ = 4160 VV₂ = 480 V

I_LV = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 4:1 has 480 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 = 480 VR_L = 12 Ω

I₁ = A

5.Hard

A single-phase 100 kVA transformer has a core loss of 400 W. At rated load and a power factor of 0.9 lagging its efficiency is 96%. Find the full-load copper loss P_cu,fl in watts.

S = 100 kVAP_core = 400 Wpf = 0.9η = 96%

P_cu,fl = W

6.Hard

A single-phase 250 kVA transformer has a core loss of 750 W and a copper loss of 2250 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 250 kVAP_core = 750 WP_cu,fl = 2250 W

S_η,max = kVA

Answer key

1. N₂ = 200
2. V₂ = 1600 V
3. I_LV = 312.5 A
4. I₁ = 2.5 A
5. P_cu,fl = 3350 W
6. S_η,max = 144.3 kVA

Full step-by-step solutions: practise this topic on examproblems.com.