Power Factor 2

Electricity and Magnetism Level 3

A household currently has a load profile of 6743 W 6743\text{ W} with a maximum demand of 11 KVA 11\text{ KVA} . The house requires some power factor correction and asks you to design a capacitor bank to increase the overall power factor. What size capacitor bank is required (in mF) to increase the current power factor to 0.9 lagging?

Assume the grid frequency is at 50 Hz 50 \text{ Hz} at a overall stable voltage of 230 Vln

Hint: Model of system

17.3 15.3 13.3 16.3 18.3

Brandon Louw by Brandon Louw , 29, South Africa

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1 solution

Brandon Louw
Jun 17, 2016
  • Firstly:
  • pf(old) = 6743/11000 = 0.613
  • pf(angle) = 52,19

  • Q(old) = 11000sin(52,19) = 8690,811 VAr

  • Secondly

  • S(new) = 6743/0.9 = 7492,22 VA because the active power stays constant
  • pf(angle) = 25,84
  • Q(new) = 7492,22 sin (25,84) = 3265,789 VAr
  • Q(capacitor) = Q(old) - Q(new) = 5425,12 VAr
  • Using the power equation Q = V 2 X c \frac{V^2}{Xc}
  • Xc = V 2 Q \frac{V^2}{Q} = 9,75 ohm
  • Xc = 1 2 p i f C \frac{1}{2 pi f C}
  • C = 16.3 mF
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