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 has 640 turns on its primary winding and 80 turns on its secondary winding. The primary is connected to a 1920 V AC supply. Find the secondary voltage V₂.

N₁ = 640N₂ = 80V₁ = 1920 V

V₂ = V

2.Easy

An ideal transformer must step 4800 V down to 120 V. Its primary winding has 2400 turns. How many turns N₂ does the secondary winding need?

V₁ = 4800 VV₂ = 120 VN₁ = 2400

N₂ =

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 20:1 has 4800 V applied to its primary winding. A 48 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 20:1V₁ = 4800 VR_L = 48 Ω

I₁ = A

4.Medium

A 50 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 10:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 10:1R_L = 50 Ω

R_1′ = Ω

5.Hard

A single-phase 150 kVA transformer has a core loss of 900 W. At rated load and a power factor of 0.9 lagging its efficiency is 98.2%. Find the full-load copper loss P_cu,fl in watts.

S = 150 kVAP_core = 900 Wpf = 0.9η = 98.2%

P_cu,fl = W

6.Hard

A single-phase 25 kVA transformer has a core loss of 75 W and a copper loss of 300 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 = 25 kVAP_core = 75 WP_cu,fl = 300 Wx = 0.5pf = 0.9

P_loss = W

Answer key

1. V₂ = 240 V
2. N₂ = 60
3. I₁ = 0.25 A
4. R_1′ = 5000 Ω
5. P_cu,fl = 1575 W
6. P_loss = 150 W

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