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
240 VloadP = 612 W3 A

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 240 V, 3 A and 612 W. Find the power factor cos φ of the load.

V = 240 VI = 3 AP = 612 W
cos φ =
2.Easy
PQ = ?S = V·Iφ

A single-phase load draws 17 A (rms) from a 240 V (rms) supply at a power factor of 0.65 lagging. Find the reactive power Q it takes.

V = 240 VI = 17 Apf = cos φ = 0.65
Q = var
3.Medium
P = 30 kWQ = ?Sφ

A single-phase motor takes 30 kW at a power factor of 0.85 lagging from a 230 V supply. Find the reactive power Q it draws.

P = 30 kWpf = 0.85V = 230 V
Q = kvar
4.Medium
P = 7 kWQ = ?Sφ

A single-phase motor takes 7 kW at a power factor of 0.7 lagging from a 400 V supply. Find the reactive power Q it draws.

P = 7 kWpf = 0.7V = 400 V
Q = kvar
5.Hard
230 V60 Hzload21 kW, 0.75C220 µFI

A single-phase load takes 21 kW at a power factor of 0.75 lagging from a 230 V, 60 Hz supply. A 220 µF capacitor is connected in parallel with the load. Find the new power factor cos φ seen by the supply.

P = 21 kWpf1 = 0.75V = 230 Vf = 60 HzC = 220 µF
cos φ =
6.Hard
P = 5 kWQ1​S1​φ1​QC​

A single-phase load takes 5 kW at a power factor of 0.8 lagging from a 400 V, 60 Hz supply. A capacitor connected in parallel raises the power factor to 0.92. Find the reactive power QC the capacitor must supply.

P = 5 kWpf1 = 0.8pf2 = 0.92V = 400 Vf = 60 Hz
QC = kvar

Answer key

  1. 1. cos φ = 0.85
  2. 2. Q = 3101 var
  3. 3. Q = 18.59 kvar
  4. 4. Q = 7.141 kvar
  5. 5. cos φ = 0.8296
  6. 6. QC = 1.62 kvar

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