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 80 turns on its primary winding and 40 turns on its secondary winding. The primary is connected to a 480 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 40V₁ = 480 V

V₂ = V

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 250 kVA, 10000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 250 kVAV₁ = 10000 VV₂ = 400 V

I_LV = A

4.Medium

A 50 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 8:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 8:1R_L = 50 Ω

R_1′ = Ω

5.Hard

A single-phase 200 kVA transformer has a core loss of 600 W and a copper loss of 1200 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 600 WP_cu,fl = 1200 W

S_η,max = kVA

6.Hard

A single-phase 75 kVA transformer has a core loss of 225 W and a copper loss of 675 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.9 lagging. Find the total losses P_loss in watts at this load.

S = 75 kVAP_core = 225 WP_cu,fl = 675 Wx = 0.25pf = 0.9

P_loss = W

Answer key

1. V₂ = 240 V
2. V₂ = 10000 V
3. I_LV = 625 A
4. R_1′ = 3200 Ω
5. S_η,max = 141.4 kVA
6. P_loss = 267.2 W

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