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 200 turns on its primary winding and 1600 turns on its secondary winding. The primary is connected to a 240 V AC supply. Find the secondary voltage V₂.

N₁ = 200N₂ = 1600V₁ = 240 V

V₂ = V

2.Easy

An ideal transformer has 1250 turns on its primary winding and 50 turns on its secondary winding. The primary is connected to a 10000 V AC supply. Find the secondary voltage V₂.

N₁ = 1250N₂ = 50V₁ = 10000 V

V₂ = V

3.Medium

A 2 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 6:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 6:1R_L = 2 Ω

R_1′ = Ω

4.Medium

A single-phase 250 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 250 kVAV₁ = 2400 VV₂ = 240 V

I_HV = A

5.Hard

A single-phase 150 kVA transformer has a core loss of 750 W and a copper loss of 1125 W at rated load. It supplies 50% of its rated kVA at a power factor of 0.85 lagging. Find the total losses P_loss in watts at this load.

S = 150 kVAP_core = 750 WP_cu,fl = 1125 Wx = 0.5pf = 0.85

P_loss = W

6.Hard

A single-phase 250 kVA transformer has a core loss of 1250 W and a copper loss of 3125 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 250 kVAP_core = 1250 WP_cu,fl = 3125 W

S_η,max = kVA

Answer key

1. V₂ = 1920 V
2. V₂ = 400 V
3. R_1′ = 72 Ω
4. I_HV = 104.2 A
5. P_loss = 1031 W
6. S_η,max = 158.1 kVA

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