AC power & power factor worksheet with answers

Free printable AC power & power factor 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
P = ?QS = V·Iφ

A single-phase load draws 12 A (rms) from a 240 V (rms) supply at a power factor of 0.8 lagging. Find the real power P it takes.

V = 240 VI = 12 Apf = cos φ = 0.8
P = W
2.Easy
400 Vload9 kW, 4 kvarI = ?

A single-phase load connected to a 400 V supply takes 9 kW and 4 kvar. Find the current I drawn from the supply.

V = 400 VP = 9 kWQ = 4 kvar
I = A
3.Medium
240 VZ9 + j12 ΩI

A load with impedance Z = 9 + j12 Ω is connected to a 240 V (rms) single-phase supply. Find the real power P it absorbs.

V = 240 VZ = 9 + j12 Ω
P = W
4.Medium
P = 3 kWQSφ

A single-phase motor takes 3 kW at a power factor of 0.9 lagging from a 240 V supply. Find the line current I.

P = 3 kWpf = 0.9V = 240 V
I = A
5.Hard
P1​ = 4 kWQ1​S1​φ

A 15 kVA single-phase transformer supplies a load of 4 kW at a power factor of 0.7 lagging. How much extra real power ΔP can be added as a resistive (unity power factor) load before the transformer reaches its kVA rating?

Smax = 15 kVAP1 = 4 kWpf1 = 0.7
ΔP = kW
6.Hard
P1​ = 41 kWQ1​S1​φ

A 150 kVA single-phase transformer supplies a load of 41 kW at a power factor of 0.85 lagging. How much extra real power ΔP can be added as a resistive (unity power factor) load before the transformer reaches its kVA rating?

Smax = 150 kVAP1 = 41 kWpf1 = 0.85
ΔP = kW

Answer key

  1. 1. P = 2304 W
  2. 2. I = 24.62 A
  3. 3. P = 2304 W
  4. 4. I = 13.89 A
  5. 5. ΔP = 10.43 kW
  6. 6. ΔP = 106.8 kW

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