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 120 V. Its primary winding has 160 turns. How many turns N₂ does the secondary winding need?

V₁ = 960 VV₂ = 120 VN₁ = 160

N₂ =

2.Easy

An ideal transformer has 80 turns on its primary winding and 320 turns on its secondary winding. The primary is connected to a 230 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 320V₁ = 230 V

V₂ = V

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 1200 V applied to its primary winding. A 4 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 10:1V₁ = 1200 VR_L = 4 Ω

I₁ = A

4.Medium

A single-phase 250 kVA, 4800/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_LV in the low-voltage winding.

S = 250 kVAV₁ = 4800 VV₂ = 240 V

I_LV = A

5.Hard

A single-phase 75 kVA transformer has a core loss of 225 W and a copper loss of 562.5 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 = 75 kVAP_core = 225 WP_cu,fl = 562.5 Wx = 0.25pf = 0.85

P_loss = W

6.Hard

A single-phase 500 kVA transformer has a core loss of 1500 W. At rated load and a power factor of 0.85 lagging its efficiency is 98.8%. Find the full-load copper loss P_cu,fl in watts.

S = 500 kVAP_core = 1500 Wpf = 0.85η = 98.8%

P_cu,fl = W

Answer key

1. N₂ = 20
2. V₂ = 920 V
3. I₁ = 3 A
4. I_LV = 1042 A
5. P_loss = 260.2 W
6. P_cu,fl = 3662 W

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