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 3000 turns on its secondary winding. The primary is connected to a 690 V AC supply. Find the secondary voltage V₂.

N₁ = 120N₂ = 3000V₁ = 690 V

V₂ = V

2.Easy

An ideal transformer must step 11500 V down to 230 V. Its primary winding has 2000 turns. How many turns N₂ does the secondary winding need?

V₁ = 11500 VV₂ = 230 VN₁ = 2000

N₂ =

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 5:1 has 600 V applied to its primary winding. A 48 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 5:1V₁ = 600 VR_L = 48 Ω

I₁ = A

4.Medium

A single-phase 50 kVA, 4160/480 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 50 kVAV₁ = 4160 VV₂ = 480 V

I_HV = A

5.Hard

A single-phase 250 kVA transformer has a core loss of 750 W and a copper loss of 2250 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 = 250 kVAP_core = 750 WP_cu,fl = 2250 Wx = 0.25pf = 0.85

P_loss = W

6.Hard

A single-phase 75 kVA transformer has a core loss of 300 W and a copper loss of 1200 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 300 WP_cu,fl = 1200 W

S_η,max = kVA

Answer key

1. V₂ = 17250 V
2. N₂ = 40
3. I₁ = 0.5 A
4. I_HV = 12.02 A
5. P_loss = 890.6 W
6. S_η,max = 37.5 kVA

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