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 120 turns on its primary winding and 960 turns on its secondary winding. The primary is connected to a 110 V AC supply. Find the secondary voltage V₂.

N₁ = 120N₂ = 960V₁ = 110 V

V₂ = V

2.Easy

An ideal transformer has 400 turns on its primary winding and 80 turns on its secondary winding. The primary is connected to a 2000 V AC supply. Find the secondary voltage V₂.

N₁ = 400N₂ = 80V₁ = 2000 V

V₂ = V

3.Medium

A single-phase 10 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 10 kVAV₁ = 2400 VV₂ = 240 V

I_HV = A

4.Medium

A 16 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 = 16 Ω

R_1′ = Ω

5.Hard

A single-phase 50 kVA transformer has a core loss of 400 W. At rated load and a power factor of 0.8 lagging its efficiency is 98%. Find the full-load copper loss P_cu,fl in watts.

S = 50 kVAP_core = 400 Wpf = 0.8η = 98%

P_cu,fl = W

6.Hard

A single-phase 25 kVA transformer has a core loss of 125 W and a copper loss of 375 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 25 kVAP_core = 125 WP_cu,fl = 375 W

S_η,max = kVA

Answer key

1. V₂ = 880 V
2. V₂ = 400 V
3. I_HV = 4.167 A
4. R_1′ = 1600 Ω
5. P_cu,fl = 416.3 W
6. S_η,max = 14.43 kVA

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