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.

New worksheetPractise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________   Date: ____________

1.Easy
P = ?QS = V·Iφ

A single-phase load draws 2 A (rms) from a 240 V (rms) supply at a power factor of 0.65 lagging. Find the real power P it takes.

V = 240 VI = 2 Apf = cos φ = 0.65
P = W
2.Easy
P = ?QS = V·Iφ

A single-phase load draws 20 A (rms) from a 400 V (rms) supply at a power factor of 0.9 lagging. Find the real power P it takes.

V = 400 VI = 20 Apf = cos φ = 0.9
P = W
3.Medium
P = 30 kWQ = ?Sφ

A single-phase motor takes 30 kW at a power factor of 0.9 lagging from a 400 V supply. Find the reactive power Q it draws.

P = 30 kWpf = 0.9V = 400 V
Q = kvar
4.Medium
240 V13 kW, 0.8220 kW, 0.8I = ?

Two loads are connected in parallel to a 240 V single-phase supply: a 3 kW load at a power factor of 0.8 lagging and a 20 kW load at a power factor of 0.8 lagging. Find the total current I drawn from the supply.

V = 240 VP1 = 3 kW, pf1 = 0.8 laggingP2 = 20 kW, pf2 = 0.8 lagging
I = A
5.Hard
400 V60 Hzload8 kW, 0.75C22 µFI = ?

A single-phase load takes 8 kW at a power factor of 0.75 lagging from a 400 V, 60 Hz supply. A 22 µF capacitor is connected in parallel with the load. Find the new line current I.

P = 8 kWpf1 = 0.75V = 400 Vf = 60 HzC = 22 µF
I = A
6.Hard
P1​ = 31 kWQ1​S1​φ

A 100 kVA single-phase transformer supplies a load of 31 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 = 100 kVAP1 = 31 kWpf1 = 0.85
ΔP = kW

Answer key

  1. 1. P = 312 W
  2. 2. P = 7200 W
  3. 3. Q = 14.53 kvar
  4. 4. I = 119.8 A
  5. 5. I = 24.6 A
  6. 6. ΔP = 67.14 kW

Full step-by-step solutions: practise this topic on examproblems.com.