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
230 VloadP = 1518 W11 A

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 230 V, 11 A and 1518 W. Find the reactive power Q taken by the load.

V = 230 VI = 11 AP = 1518 W
Q = var
2.Easy
PQ = ?S = V·Iφ

A single-phase load draws 19 A (rms) from a 230 V (rms) supply at a power factor of 0.85 lagging. Find the reactive power Q it takes.

V = 230 VI = 19 Apf = cos φ = 0.85
Q = var
3.Medium
120 VZ7 + j24 ΩI

A load with impedance Z = 7 + j24 Ω is connected to a 120 V (rms) single-phase supply. Find the reactive power Q it absorbs.

V = 120 VZ = 7 + j24 Ω
Q = var
4.Medium
P = 36 kWQSφ

A single-phase motor takes 36 kW at a power factor of 0.8 lagging from a 230 V supply. Find the line current I.

P = 36 kWpf = 0.8V = 230 V
I = A
5.Hard
P = 30 kWQ1​S1​φ1​QC​

A single-phase load takes 30 kW at a power factor of 0.8 lagging from a 230 V, 50 Hz supply. A capacitor connected in parallel raises the power factor to 0.95. Find the new line current Inew.

P = 30 kWpf1 = 0.8pf2 = 0.95V = 230 Vf = 50 Hz
Inew = A
6.Hard
230 V50 Hzload22 kW, 0.6C330 µFI = ?

A single-phase load takes 22 kW at a power factor of 0.6 lagging from a 230 V, 50 Hz supply. A 330 µF capacitor is connected in parallel with the load. Find the new line current I.

P = 22 kWpf1 = 0.6V = 230 Vf = 50 HzC = 330 µF
I = A

Answer key

  1. 1. Q = 2024 var
  2. 2. Q = 2302 var
  3. 3. Q = 553 var
  4. 4. I = 195.7 A
  5. 5. Inew = 137.3 A
  6. 6. I = 141.1 A

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