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 80 turns on its primary winding and 1600 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 1600V₁ = 690 V

V₂ = V

2.Easy

An ideal transformer has 60 turns on its primary winding and 120 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 60N₂ = 120V₁ = 400 V

V₂ = V

3.Medium

A 4 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 12:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 12:1R_L = 4 Ω

R_1′ = Ω

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 20:1 has 4800 V applied to its primary winding. A 12 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 20:1V₁ = 4800 VR_L = 12 Ω

I₁ = A

5.Hard

A single-phase 100 kVA transformer has a core loss of 500 W and a copper loss of 1500 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.8 lagging. Find the total losses P_loss in watts at this load.

S = 100 kVAP_core = 500 WP_cu,fl = 1500 Wx = 0.5pf = 0.8

P_loss = W

6.Hard

A single-phase 100 kVA transformer has a core loss of 300 W and a copper loss of 750 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 100 kVAP_core = 300 WP_cu,fl = 750 W

S_η,max = kVA

Answer key

1. V₂ = 13800 V
2. V₂ = 800 V
3. R_1′ = 576 Ω
4. I₁ = 1 A
5. P_loss = 875 W
6. S_η,max = 63.25 kVA

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