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 4600 V down to 230 V. Its primary winding has 800 turns. How many turns N₂ does the secondary winding need?

V₁ = 4600 VV₂ = 230 VN₁ = 800

N₂ =

2.Easy

An ideal transformer must step 460 V down to 230 V. Its primary winding has 240 turns. How many turns N₂ does the secondary winding need?

V₁ = 460 VV₂ = 230 VN₁ = 240

N₂ =

3.Medium

A 5 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 12:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 12:1R_L = 5 Ω

R_1′ = Ω

4.Medium

A single-phase 15 kVA, 11000/400 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 15 kVAV₁ = 11000 VV₂ = 400 V

I_HV = A

5.Hard

A single-phase 25 kVA transformer has a core loss of 75 W and a copper loss of 225 W at rated load. It supplies 25% of its rated kVA at a power factor of 0.9 lagging. Find the total losses P_loss in watts at this load.

S = 25 kVAP_core = 75 WP_cu,fl = 225 Wx = 0.25pf = 0.9

P_loss = W

6.Hard

A single-phase 75 kVA transformer has a core loss of 300 W. At rated load and a power factor of 0.9 lagging its efficiency is 98%. Find the full-load copper loss P_cu,fl in watts.

S = 75 kVAP_core = 300 Wpf = 0.9η = 98%

P_cu,fl = W

Answer key

1. N₂ = 40
2. N₂ = 120
3. R_1′ = 720 Ω
4. I_HV = 1.364 A
5. P_loss = 89.06 W
6. P_cu,fl = 1078 W

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