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 Vload23.5 kW, 9.5 kvarI = ?

A single-phase load connected to a 120 V supply takes 23.5 kW and 9.5 kvar. Find the current I drawn from the supply.

V = 120 VP = 23.5 kWQ = 9.5 kvar
I = A
2.Easy
PQ = ?S = V·Iφ

A single-phase load draws 19 A (rms) from a 120 V (rms) supply at a power factor of 0.8 lagging. Find the reactive power Q it takes.

V = 120 VI = 19 Apf = cos φ = 0.8
Q = var
3.Medium
120 VZ8 + j6 ΩI

A load with impedance Z = 8 + j6 Ω is connected to a 120 V (rms) single-phase supply. Find the reactive power Q it absorbs.

V = 120 VZ = 8 + j6 Ω
Q = var
4.Medium
P = 5 kWQSφ

A single-phase motor takes 5 kW at a power factor of 0.6 lagging from a 400 V supply. Find the line current I.

P = 5 kWpf = 0.6V = 400 V
I = A
5.Hard
P = 50 kWQ1​S1​φ1​QC​

A single-phase load takes 50 kW at a power factor of 0.6 lagging from a 230 V, 60 Hz supply. A capacitor connected in parallel raises the power factor to 0.98. Find the reactive power QC the capacitor must supply.

P = 50 kWpf1 = 0.6pf2 = 0.98V = 230 Vf = 60 Hz
QC = kvar
6.Hard
P = 50 kWQ1​S1​φ1​QC​

A single-phase load takes 50 kW at a power factor of 0.6 lagging from a 400 V, 50 Hz supply. A capacitor connected in parallel raises the power factor to 0.98. Find the capacitance C needed.

P = 50 kWpf1 = 0.6pf2 = 0.98V = 400 Vf = 50 Hz
C = µF

Answer key

  1. 1. I = 211.2 A
  2. 2. Q = 1368 var
  3. 3. Q = 864 var
  4. 4. I = 20.83 A
  5. 5. QC = 56.51 kvar
  6. 6. C = 1124 µF

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