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
120 VloadP = 1824 W19 A

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 120 V, 19 A and 1824 W. Find the reactive power Q taken by the load.

V = 120 VI = 19 AP = 1824 W
Q = var
2.Easy
120 VloadP = 1392 W14.5 A

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 120 V, 14.5 A and 1392 W. Find the power factor cos φ of the load.

V = 120 VI = 14.5 AP = 1392 W
cos φ =
3.Medium
P = 12 kWQSφ

A single-phase motor takes 12 kW at a power factor of 0.65 lagging from a 240 V supply. Find the line current I.

P = 12 kWpf = 0.65V = 240 V
I = A
4.Medium
P = 24 kWQ = ?Sφ

A single-phase motor takes 24 kW at a power factor of 0.75 lagging from a 240 V supply. Find the reactive power Q it draws.

P = 24 kWpf = 0.75V = 240 V
Q = kvar
5.Hard
P = 45 kWQ1​S1​φ1​QC​

A single-phase load takes 45 kW at a power factor of 0.7 lagging from a 400 V, 60 Hz supply. A capacitor connected in parallel raises the power factor to 0.98. Find the new line current Inew.

P = 45 kWpf1 = 0.7pf2 = 0.98V = 400 Vf = 60 Hz
Inew = A
6.Hard
24 V1000 HzRs​ = 4 ΩXs​ = j3 ΩZL​ = ?

A 24 V (rms), 1000 Hz source has an internal impedance Zs = 4 + j3 Ω. The load impedance ZL can be chosen freely. Find the maximum real power Pmax that can be delivered to the load.

Vs = 24 V (rms)f = 1000 HzZs = 4 + j3 Ω
Pmax = W

Answer key

  1. 1. Q = 1368 var
  2. 2. cos φ = 0.8
  3. 3. I = 76.92 A
  4. 4. Q = 21.17 kvar
  5. 5. Inew = 114.8 A
  6. 6. Pmax = 36 W

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