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 must step 960 V down to 240 V. Its primary winding has 160 turns. How many turns N₂ does the secondary winding need?

V₁ = 960 VV₂ = 240 VN₁ = 160

N₂ =

2.Easy

An ideal transformer has 600 turns on its primary winding and 120 turns on its secondary winding. The primary is connected to a 600 V AC supply. Find the secondary voltage V₂.

N₁ = 600N₂ = 120V₁ = 600 V

V₂ = V

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 5:1 has 1200 V applied to its primary winding. A 60 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 5:1V₁ = 1200 VR_L = 60 Ω

I₁ = A

4.Medium

A single-phase 75 kVA, 480/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 75 kVAV₁ = 480 VV₂ = 240 V

I_HV = A

5.Hard

A single-phase 100 kVA transformer has a core loss of 500 W and a copper loss of 1000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 100 kVAP_core = 500 WP_cu,fl = 1000 W

S_η,max = kVA

6.Hard

A single-phase 50 kVA transformer has a core loss of 150 W and a copper loss of 450 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.85 lagging. Find the total losses P_loss in watts at this load.

S = 50 kVAP_core = 150 WP_cu,fl = 450 Wx = 0.25pf = 0.85

P_loss = W

Answer key

1. N₂ = 40
2. V₂ = 120 V
3. I₁ = 0.8 A
4. I_HV = 156.3 A
5. S_η,max = 70.71 kVA
6. P_loss = 178.1 W

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