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
240 VloadP = 1512 W9 A

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 240 V, 9 A and 1512 W. Find the power factor cos φ of the load.

V = 240 VI = 9 AP = 1512 W
cos φ =
2.Easy
400 Vload17.5 kW, 17 kvarI = ?

A single-phase load connected to a 400 V supply takes 17.5 kW and 17 kvar. Find the current I drawn from the supply.

V = 400 VP = 17.5 kWQ = 17 kvar
I = A
3.Medium
P = 20 kWQ = ?Sφ

A single-phase motor takes 20 kW at a power factor of 0.7 lagging from a 230 V supply. Find the reactive power Q it draws.

P = 20 kWpf = 0.7V = 230 V
Q = kvar
4.Medium
P = 28 kWQSφ

A single-phase motor takes 28 kW at a power factor of 0.85 lagging from a 240 V supply. Find the line current I.

P = 28 kWpf = 0.85V = 240 V
I = A
5.Hard
P = 15 kWQ1​S1​φ1​QC​

A single-phase load takes 15 kW at a power factor of 0.65 lagging from a 230 V, 50 Hz supply. A capacitor connected in parallel raises the power factor to 0.95. Find the reactive power QC the capacitor must supply.

P = 15 kWpf1 = 0.65pf2 = 0.95V = 230 Vf = 50 Hz
QC = kvar
6.Hard
P = 5 kWQ1​S1​φ1​QC​

A single-phase load takes 5 kW at a power factor of 0.6 lagging from a 230 V, 50 Hz supply. A capacitor connected in parallel raises the power factor to 0.92. Find the new line current Inew.

P = 5 kWpf1 = 0.6pf2 = 0.92V = 230 Vf = 50 Hz
Inew = A

Answer key

  1. 1. cos φ = 0.7
  2. 2. I = 60.99 A
  3. 3. Q = 20.4 kvar
  4. 4. I = 137.3 A
  5. 5. QC = 12.61 kvar
  6. 6. Inew = 23.63 A

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