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 = 2513 W11.5 A

A voltmeter, an ammeter and a wattmeter connected to a single-phase inductive load read 230 V, 11.5 A and 2513 W. Find the reactive power Q taken by the load.

V = 230 VI = 11.5 AP = 2513 W
Q = var
2.Easy
P = 50 kWQ = 26.5 kvarS = ?φ

A load takes 50 kW of real power and 26.5 kvar of reactive power (lagging). Find the apparent power S.

P = 50 kWQ = 26.5 kvar
S = kVA
3.Medium
P = 26 kWQSφ

A single-phase motor takes 26 kW at a power factor of 0.6 lagging from a 240 V supply. Find the line current I.

P = 26 kWpf = 0.6V = 240 V
I = A
4.Medium
P = 2 kWQSφ

A single-phase motor takes 2 kW at a power factor of 0.7 lagging from a 400 V supply. Find the line current I.

P = 2 kWpf = 0.7V = 400 V
I = A
5.Hard
240 V50 Hzload21 kW, 0.8C220 µFI = ?

A single-phase load takes 21 kW at a power factor of 0.8 lagging from a 240 V, 50 Hz supply. A 220 µF capacitor is connected in parallel with the load. Find the new line current I.

P = 21 kWpf1 = 0.8V = 240 Vf = 50 HzC = 220 µF
I = A
6.Hard
P1​ = 7 kWQ1​S1​φ

A 15 kVA single-phase transformer supplies a load of 7 kW at a power factor of 0.85 lagging. How much extra real power ΔP can be added as a resistive (unity power factor) load before the transformer reaches its kVA rating?

Smax = 15 kVAP1 = 7 kWpf1 = 0.85
ΔP = kW

Answer key

  1. 1. Q = 825.1 var
  2. 2. S = 56.59 kVA
  3. 3. I = 180.6 A
  4. 4. I = 7.143 A
  5. 5. I = 100.3 A
  6. 6. ΔP = 7.359 kW

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