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 800 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 9200 V AC supply. Find the secondary voltage V₂.

N₁ = 800N₂ = 20V₁ = 9200 V

V₂ = V

2.Easy

An ideal transformer must step 12000 V down to 240 V. Its primary winding has 7500 turns. How many turns N₂ does the secondary winding need?

V₁ = 12000 VV₂ = 240 VN₁ = 7500

N₂ =

3.Medium

A single-phase 150 kVA, 4800/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 150 kVAV₁ = 4800 VV₂ = 240 V

I_HV = A

4.Medium

An ideal transformer with a turns ratio N₁:N₂ = 2:1 has 240 V applied to its primary winding. A 10 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 2:1V₁ = 240 VR_L = 10 Ω

I₁ = A

5.Hard

A single-phase 50 kVA transformer has a core loss of 400 W and a copper loss of 600 W at rated load. It supplies 75% of its rated kVA at a power factor of 0.8 lagging. Find the total losses P_loss in watts at this load.

S = 50 kVAP_core = 400 WP_cu,fl = 600 Wx = 0.75pf = 0.8

P_loss = W

6.Hard

A single-phase 50 kVA transformer has a core loss of 200 W and a copper loss of 500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 50 kVAP_core = 200 WP_cu,fl = 500 W

S_η,max = kVA

Answer key

1. V₂ = 230 V
2. N₂ = 150
3. I_HV = 31.25 A
4. I₁ = 6 A
5. P_loss = 737.5 W
6. S_η,max = 31.62 kVA

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