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 1600 turns. How many turns N₂ does the secondary winding need?

V₁ = 4600 VV₂ = 230 VN₁ = 1600

N₂ =

2.Easy

An ideal transformer has 250 turns on its primary winding and 2000 turns on its secondary winding. The primary is connected to a 230 V AC supply. Find the secondary voltage V₂.

N₁ = 250N₂ = 2000V₁ = 230 V

V₂ = V

3.Medium

An amplifier with an output resistance of 125 Ω drives a 5 Ω loudspeaker through an ideal transformer. For maximum power transfer the loudspeaker must look like 125 Ω from the amplifier. Find the turns ratio a = N₁/N₂.

R_s = 125 ΩR_L = 5 Ω

a =

4.Medium

A single-phase 50 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 = 50 kVAV₁ = 11000 VV₂ = 400 V

I_HV = A

5.Hard

A single-phase 200 kVA transformer has a core loss of 1000 W and a copper loss of 1500 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 200 kVAP_core = 1000 WP_cu,fl = 1500 W

S_η,max = kVA

6.Hard

A single-phase 150 kVA transformer has a core loss of 1200 W and a copper loss of 2400 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 = 150 kVAP_core = 1200 WP_cu,fl = 2400 Wx = 0.25pf = 0.9

P_loss = W

Answer key

1. N₂ = 80
2. V₂ = 1840 V
3. a = 5
4. I_HV = 4.545 A
5. S_η,max = 163.3 kVA
6. P_loss = 1350 W

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