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 10000 turns on its primary winding and 200 turns on its secondary winding. The primary is connected to a 6000 V AC supply. Find the secondary voltage V₂.

N₁ = 10000N₂ = 200V₁ = 6000 V

V₂ = V

2.Easy

An ideal transformer must step 4800 V down to 240 V. Its primary winding has 1200 turns. How many turns N₂ does the secondary winding need?

V₁ = 4800 VV₂ = 240 VN₁ = 1200

N₂ =

3.Medium

A 2 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 = 2 Ω

R_1′ = Ω

4.Medium

A single-phase 100 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 = 100 kVAV₁ = 10000 VV₂ = 400 V

I_LV = A

5.Hard

A single-phase 25 kVA transformer has a core loss of 150 W and a copper loss of 450 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 25 kVAP_core = 150 WP_cu,fl = 450 W

S_η,max = kVA

6.Hard

A single-phase 75 kVA transformer has a core loss of 300 W and a copper loss of 750 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.95 lagging. Find the total losses P_loss in watts at this load.

S = 75 kVAP_core = 300 WP_cu,fl = 750 Wx = 0.75pf = 0.95

P_loss = W

Answer key

1. V₂ = 120 V
2. N₂ = 60
3. R_1′ = 200 Ω
4. I_LV = 250 A
5. S_η,max = 14.43 kVA
6. P_loss = 721.9 W

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